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Technical information - glassware

     Glassware                                                                  Chemical Composition
     Glass is an inorganic mixture of metal oxides fused together at high       Pyrex® glass has the following typical composition (% by weight):
     temperatures, which upon cooling, solidifies into the clear, rigid, non-
     crystalline, versatile material known widely across the globe.             	          SiO2		                =	         80.6%
                                                                                	          B2O3		                =	         13.0%
                                                                                	          Na2O		                =	         4.0%
                                                                                	          Al2O3		               =	         2.3%


                                                                                Physical Properties
                                                                                Coefficient of expansion (20 – 300°C)	            =	    3.3x10-6K-1
                                                                                Density	                                          =	    2.23g/cm3
                                                                                Refractive index (Sodium D line)	                 =	    1.474
                                                                                Dielectric constant (1MHz, 20°C)	                 =	    4.6
                                                                                Specific heat (20°C)	                             =	    750J/kg°C
                                                                                Thermal conductivity (20°C)	                      =	    1.14W/m°C
                                                                                Poissons Ratio (25 - 400°C)	                      =	    0.2


                                                                                Chemical Properties
                                                                                Pyrex® borosilicate glass has a very high resistance to attack from
                                                                                water, acids, salt solutions, halogens and organic solvents. Only
                                                                                hydrofluoric acid, hot concentrated phosphoric acid and strong
                                                                                alkaline solutions cause appreciable corrosion of the glass.

     Pyrex® Borosilicate Glass                                                  Hydrolytic resistance
     All Pyrex®, Quickfit®, SVL® and many MBL® branded SciLabware
                                                                                For many applications, it is important that laboratory glassware
     products are manufactured from borosilicate glass (unless otherwise
                                                                                has excellent hydrolytic resistance; e.g. during steam sterilisation
     stated).
                                                                                procedures, where repeated exposure to water vapour at high
                                                                                temperature can leach out alkali (Na+) ions. Pyrex® borosilicate glass
     Standards                                                                  has a relatively low alkali metal oxide content and consequently
                                                                                a high resistance to attack from water. Pyrex® fits into Class 1 of
     Pyrex® is a borosilicate glass which meets the specifications of the
                                                                                glasses for hydrolytic resistance according to ISO 719 (98°C) and ISO
     following standards:
                                                                                720 (121°C).

     	    ISO 3585, DIN 12217	               Type 3.3 borosilicate glass
                                                                                Acid resistance
     	 ASTM E-438	                           Type 1 Class A borosilicate 	
     		                                      glass                              Glasses with a high percentage weight of silica (SiO2) are less likely
                                                                                to be attacked by acids. Pyrex® borosilicate glass is over 80% silica
     	    US Pharmacopoeia	                  Type 1 borosilicate glass
                                                                                and therefore remarkably resistant to acids (with the exception of
     	    European Pharmacopoeia	            Type 1 glass                       hot concentrated phosphoric acid and hydrofluoric acid). Glass is
                                                                                separated into 4 acid resistance classes and Pyrex® corresponds to
     Due to the demanding conditions that borosilicate glass is subjected       Class 1 in accordance with DIN 12116 and meets the requirements
     to, maximum chemical toughness, minimum thermal expansion and              of ISO 1776.
     high resistance to thermal shock make Pyrex® the ideal material for
     use in the laboratory.                                                     Alkali resistance
     Many SciLabware Ltd products also conform to other standards set
                                                                                Alkaline solutions attack all glasses and Pyrex® can be classified as
     out for laboratory glassware; for example beakers comply to ISO
                                                                                moderately resistant. The alkali resistance of Pyrex® borosilicate
     3819 and volumetric flasks comply to ISO 1042 and DIN 12664.
                                                                                glass meets Class 2 requirements as defined by ISO 695 and DIN
     Typically these standards will specify not only glass type, but also
                                                                                52322.
     dimensional detail, volumetric accuracy and tolerances.




12
Technical information - glassware

                          Temperature resistance                                                                                                      Glassblowing data
                          Pyrex® borosilicate glass has excellent thermal properties at both                                                          Listed in this catalogue are some Pyrex® and Quickfit® items that are
                          high and low temperatures. The maximum recommended working                                                                  suitable for further manipulation and processing. These items include
                          temperature for laboratory glassware manufactured from Pyrex® is                                                            stopcocks, ground glass joints, sinters and screwthreads. When
                          500°C (for short periods of time only). Special care should be taken                                                        working with these products, Glassblowers may find the following
                          at temperatures above 150°C to ensure both heating and cooling are                                                          information useful regarding Pyrex® borosilicate glass:
                          achieved in a slow and uniform manner (see Care and Maintenance
                          of Laboratory Glassware).                                                                                                   	         Working point	        =	         1252°C
                          Pyrex® also performs excellently at lower temperatures. Pyrex® can                                                          	         Softening point	      =	         821°C
                          withstand conditions down to approximately -192°C and is suitable                                                           	         Annealing point	      =	         565°C
                          for use with liquid nitrogen. In normal laboratory use, temperatures                                                        	         Strain point	         =	         510°C
                          of -70°C are easily sustained for lengthy periods. Again special care
                          should be taken to avoid sudden changes in temperature, and cooling
                          should be achieved in a slow uniform manner.                                                                                Pyrex® bottles with retrace codes
                                                                                                                                                      Pyrex® media bottles are
                          Optical data                                                                                                                used in many laboratory
                                                                                                                                                      processes but they are also
                          Pyrex® borosilicate glass is clear and colourless in appearance and
                                                                                                                                                      used in packaging, which
                          thus transmits light through the visible range of the spectrum. This
                                                                                                                                                      often has to meet the
                          quality makes it ideal for work involving photochemical reactions,
                                                                                                                                                      strict requirements of the
                          for example chlorinations. The graph (above) shows the degree of
                                                                                                                                                      United States and European
                          transmission of light as a function of wavelength in the ultra-violet,
                                                                                                                                                      Pharmacopoeias (USP and
                          visible and infra-red regions of the spectrum. For the majority of
                                                                                                                                                      EP), GMP and ISO 9000.
                          glassware detailed in our catalogue, the thickness of the glass is
                          2–5mm.                                                                                                                      To meet these stringent
                                                                                                                                                      requirements, all Pyrex®
                    100                                                                                                     1-000
                          90
                                                                                      2mm
                                                                                                                            1-046
                                                                                                                                                      media bottles are now
                          80                                                          5mm                                   1-097                     printed with a ‘Retrace
Percentage Transmission




                          70                                                                                                1-155
                                                                                                                                                      Code’. This retrace code
                                                                                                                                    Optical Density




                          60                                                                                                1-222

                          50                                                                                                1-301                     allows the product to
                          40                                                                                                1-396
                                                                                                                                                      be traced to the point of
                          30                                                                                                1-532
                          20                                                                                                1-696
                                                                                                                                                      production and the matching batch. This code is our commitment to
                          10                                                                                                1-699                     support your quality management documentation and can be easily
                           0
                               0.3       0.4    0.5   0.6   0.7   0.8     0.9    1      2           3         4       5
                                                                                                                            1-000
                                                                                                                                                      downloaded from the SciLabware web site by keying in the 8-digit
                                                                          Wavelength (µm)
                                                                                                                                                      code shown on the side of the bottle. ‘Retrace’ codes can be found
                                                                                                                                                      on all Pyrex® 1516/: 1517/: 1518/: 1519/: and 1520/: series bottles.
                          Amber coated Pyrex® glassware
                          Several SciLabware glass products, including media-lab bottles and
                          volumetric flasks, are available in amber-coated glass. The glassware                                                       Pyrex® bottles with plastic coating
                          is coated on the exterior surface with a brown diffusion colour which                                                       The Pyrex® range of 1518: media-lab bottles have a plastic coating
                          results in a strong absorption in the short wavelength region up to                                                                                               to provide protection from
                          500nm. This feature is particularly useful when handling reagents                                                                                                 mechanical impact and to
                          that are light-sensitive.                                                                                                                                         help reduce leakage of the
                                                                                                                                                                                            contents should the glass
                                               ultraviolet range                visable range             infrared range
                               100                                                                                                                                                          break.
                                 90                                                                                                                                                           The maximum working
                                 80                                                                                                                                                           temperature for these bottles
                                70                                                                                                                                                            is 135°C but long term
            transmission(%)




                                60                                                                                                                                                            exposure (>30 mins) should
                                                                                                                                                                                              be avoided.
                                50
                                                                                                         5000ml clear                                                                         Avoid exposure to direct heat
                                40                                                                       500ml clear
                                                                                                         5000ml coated
                                                                                                                                                                                              from a hotplate or a Bunsen
                                30                                                                                                                                                            flame. The 1518: media
                                                                                                         500ml coated
                                20                                                                       5000ml amber                                                                         bottle is suitable for freezing
                                10                                                                       500ml amber                                                                          at -30°C and can also be
                                     0                                                                                                                                                        used in microwave ovens.
                                         0     100    200 300           400     500     600   700       800       900 1000 1100
                                                                                                                                                      Please note that the plastic coating does not increase the permissible
                                                                         wavelength(nm)
                                                                                                                                                      pressure at which the bottles can be used and a protective screen is
                                                                                                                                                      recommended for all pressure work.




                                                                                                                                                                                                                                13
Technical information - glassware

     Centrifuge tubes                                                                 Sintered discs
     This catalogue lists a number of Pyrex® and Quickfit® centrifuge                 The SciLabware ranges of filtration glassware utilise sintered
     tubes. Within the product information for each entry we advise the               discs manufactured from Pyrex® borosilicate glass. Since they are
     maximum Relative Centrifugal Force (RCF) they can be subjected to.               manufactured from Pyrex® they are resistant to the majority of
     Before centrifuging, it is important to calculate the actual RCF values          corrosive reagents, unaffected by ammonia, sulphuric acid and other
     that will be generated. This can quickly be determined by using the              solvents that are damaging to filter paper. The sintered glassware is
     following nomogram.                                                              available in six porosity classes from 0 – 5, as outlined in the table
                                                                                      below. The pore sizes indicated, give a range of pores present within
     To calculate the RCF value at any point along the tube, measure
                                                                                      the sinter disc. Therefore, the size of particles that will be obstructed
     the radius, in mm, from the centre of the centrifuge spindle to the
                                                                                      will generally be of a size at the upper end of the range.
     particular point.
                                     RCF Values
         25,000
                                                                                       Porosity	 ISO 4793		            Pore		              Principal
                                                                             500       Grade	    designation		         index		             uses
         20,000                                                              475
                                                                             450       			                             (mic.) 	
         15,000                                                              425
                                                                             400       0	 P250		 160 - 250		                               Coarse filtration, 	
                                                                             375
                                                                             350
                                                                                       					                                               gas dispersion 		
         10,000
                               30,000                                        325       					                                               and support for 		
                               20,000                                        300
                                                                                       					                                               other filter material
          6000                                                               275
                               10,000
                                                                             250       1	 P160		 100 - 160		                               Course precipitate 	
                               5000                                          225       					                                               filtration, gas 		
          4000
                                                                             200
                                                                                       					                                               dispersion, coarse 	
          3000                 2000
                                                                                       					                                               grain material 		
                                                                             175
                               1000                                                    					                                               filtration
          2000
                               500
                                                                             150
                                                                                       2	 P100		 40 - 100		                                Medium and 		
                                                                             140
                                                                             130       					                                               crystalline precipitate 	
                               200                                           120       					                                               filtration, medium 	
          1000
                               100
                                                                             110       					                                               filtration and 		
                                                                             100
                                                                                       					                                               washing of gases
                               50                                            90

                                                                             80
                                                                                       3	 P40		 16 - 40		                                  Analytical work 		
           500                 20                                                      					                                               with medium 		
                               10
                                                                             70        					                                               precipitates	
                                                                             60        4	 P16		 10 - 16		                                  Analytical work 		
                               3
                                                                                       					                                               with fine precipitates
           200                                                               50
                                                                                       5	         P10		                4 - 10		            Bacteria filtration	
         Speed of        Relative centrifugal         Radius in mm from centre of
         Centrifuge      force (xg)                     centrifuge spindle to point
                                                                                      In addition to the above detail, sinters should be treated under
         (rpm)                                                 along tube or bottle
                                                                                      the same conditions as described in the general Pyrex® thermal
     NB: The chosen point should be the base of the tube as this area will            properties as listed on page 13.
     experience the maximum RCF.                                                      When using new sintered glassware for the first time, we recommend
     Note the radius value from the right of the table and draw a line to             a wash with hydrochloric acid followed by several rinses with distilled
     the appropriate centrifuge speed value on the left hand column. The              water to remove any residual glass dust particles from the sinter.
     RCF value is the point where the line crosses the centre column.
     The nomogram is based on the following equation:


     		                      RCF = (11.17x10-7) RN2
     	            R = Rotational radius (in mm)
     	            N = Rotational speed (in RPM)


     The allocated RCF values are for tubes in good condition. Do not
     use centrifuge tubes which are scratched, abraded or chipped as the
     strength will be seriously impaired.




14
Technical information - glassware

Sintered discs (continued)                                                Quickfit® Products
In order to select the correct sinter for any specific application, in                              Conical joints
addition to the porosity, it is also useful to know the flow rates of
liquids and gases through the sinters. These values are given in the
charts below for water and air. The data applies to 30mm diameter
filter discs. The flow rates for other disc diameters can be calculated
by multiplying the value read off by the conversion factor given in the
table below.

  Filter disc
  dia. mm 	     10	    20	    30	   40	    60	    90	 120	 150	    175
  Conversion
  factor 	      0,13	 0,55	   1	    1,5	   2,5	   4,3	 6,8	 9,7	   15
                                                                                     24/29 cone                       24/29 socket

Water flow rate
                                                                                                   Spherical joints




                                                                                        S35 ball                           S35 cup


                                                                                       Flat flange                    Screwthread




                                                                                     100mm bore flange                   28 screwthread
  Dry-air flow rate

                                                                          Conical Joints - size designation

                                                                           Size	        Actual	                 Actual 	             Nominal
                                                                           designation	 dia. of wide	           dia. of	             length of
                                                                           	            end (mm)	               narrow	              engagement 	
                                                                           		                                   end (mm)	            (mm)
                                                                           7/16 	                 7.5 	          5.9 	               16
                                                                           10/19 	            10.0 	             8.1 	               19
                                                                           12/21 	            12.5 	            10.4 	               21
                                                                           14/23 	            14.5 	            12.2 	               23
                                                                           19/26 	            18.8 	            16.2 	               26
                                                                           24/29 	            24.0 	            21.1 	               29
                                                                           29/32 	            29.2 	            26.0 	               32
                                                                           34/35 	            34.5 	            31.0 	               35
                                                                           40/38 	            40.0 	            36.2 	               38
                                                                           45/40 	            45.0 	            41.0 	               40
                                                                           50/42 	            50.0 	            45.8 	               42
                                                                           55/44 	            55.0 	            50.6 	               44
                                                                           60/46	             60.0 	            55.4 	               46




                                                                                                                                                    15
Technical information - glassware

     Quickfit® screwthread joints                                                   Quickfit® flask dimensions




                                                                   Cap




                                                                   Ring



                                                                   Washer




                                                                                    Volumetric Glassware
                    Fig 1                       Fig 2                               SciLabware Ltd manufactures two brands of volumetric glassware,
                                                                                    Pyrex® and MBL®. As the name indicates Pyrex® volumetrics are
                                                                                    manufactured solely from Pyrex® borosilicate glass. MBL® volumetric
                                                                                    products are manufactured from borosilicate and soda-lime glass.
     Screwcap assembly                                                              Soda-lime glass is generally used for Class B products
     When using screwthreads it is important that the PTFE washer is                or where long term exposure to chemicals is unlikely,
     fitted carefully and correctly. This is best achieved by opening out           e.g. one mark pipettes.
     the washer to the correct diameter using a tapered former. This                Pyrex® volumetric glassware has superior thermal and chemical
     should be carried out with the silicone rubber ring and PTFE washer            resistance and is better suited to glassware for storage of solutions,
     in position in the plastic cap as shown in Fig1. Withdraw the tapered          e.g. flasks.
     former and remove the rubber ring and washer from the cap.
                                                                                    The use of Pyrex® borosilicate glass for volumetric glassware means
     Fit each component separately to the fitting which is to be held, as           accuracy is retained over a longer working lifetime than their soda-
     shown in Fig 2, and screw the cap on to the thread. It is advisable            lime equivalents. With everyday use, volumetric glassware requires
     that the ends of all fittings should be slightly tapered or fired in a         recalibration. Soda-lime glass items will generally necessitate twice
     Bunsen flame to remove sharp edges and produce a slight taper.                 as many recalibrations as items constructed from borosilicate glass.
                                                                                    ASTM 542 and ISO 4787 international standards for calibration of
     Quickfit® flask dimensions                                                     laboratory volumetric glassware recommend that volumetric flasks
                                                                                    are recalibrated at the following intervals (or sooner if chemical
     The body diameter of Quickfit® Round Bottomed and Flat Bottomed
                                                                                    corrosion is observed): Borosilicate – 10 years; Soda-lime – 5 years.
     flasks comply with ISO 1773 (BS 6352).


     Nominal	    Approx	     Approx		 Nominal	          Approx        Approx
                                                                                    Volumetric accuracy
     capacity	   bulb	       bulb		 capacity	           bulb	          bulb         SciLabware volumetric glassware is manufactured and calibrated in
     ml	         dia. ‘a’	   height ‘b’		 ml	           dia. ‘a’     	 height ‘b’   accordance with international ISO standards to permit very accurate
     	           mm	         mm			                      mm	            mm           determination and measurement of specific volumes. They are
     5	          25 	        - 		          1000 	       132 	             115       available in two accuracy classes: Class A/AS and Class B. The two
                                                                                    classes differ in the accuracy of measurement with a Class A/AS being
     10 	        30 	        - 		          2000 	       166 	             155
                                                                                    the highest accuracy, and class B is approximately half of a class A.
     25 	        40 	        - 		          3000 	       188 	             -         Class AS has the same high tolerances as Class A, but is designed to
     50 	        50 	        40 		         5000 	       220	              -         permit more rapid outflow on burettes and pipettes.
     100 	       65 	        55 		         10000 	      279 	             -
     150 	       75 	        65 		         20000 	      345 	             -
     250 	       85 	        75 		         -	           -	                -
     500 	       105 	       95 		         -	           -	                -



16
Technical information - glassware

Inscriptions                                                             Batch certificates
SciLabware volumetric glassware is manufactured and calibrated in                                                        For our ranges of Pyrex®
accordance with international ISO requirements. All of our volumetric                                                    Class A volumetric
glassware is marked with a set of inscriptions in accordance with any                                                    flasks and cylinders and
specific standard associated with it.                                                                                    MBL® Class AS pipettes
	                                                                                                                        a downloadable batch
                                                                                                                         certificate is available
Tolerance	           Class A/AS – Highest level of accuracy.
                                                                                                                         from the SciLabware
		                   Class B – General purpose work 	calibrated to a 	                                                   website. The batch
		                   lower level of accuracy                                                                             certificate contains
Standard 	           The standard to which the product 		                                                                detailed information
		                   conforms                                                                                            pertaining to the
                                                                                                                         specific production
Graduation	          Pyrex® and MBL® volumetric glass is 		
                                                                                                                         batch including average
		                   graduated in ml (millilitres) in accordance 		
                                                                                                                         volume and standard
		                   with ISO
                                                                                                                         deviation for the batch.
IN 		                Calibrated to contain
                                                                                                                          To download a batch
EX		                 Calibrated to deliver                                                                                certificate visit www.
Blowout 	            Indication that last drop should be blown 		                                                         scilabware.com and
		                   out of jet                                          go the ‘certificates’ section then follow the links for the specified
                                                                         product. Simply enter the serial number marked on each volumetric
Temp °C		            All Pyrex® and MBL® volumetric glassware 		
                                                                         item and the batch certificate is downloaded as a pdf.
		                   is calibrated at 20°C
Certification	       All Class A/AS Works Certified glassware
		                   bears a serial number for identification            Re-calibration
		                   and traceability.                                   Normally, volumetric glassware only needs re-calibrating after
                                                                         extensive or demanding usage, which may have affected the original
                                                                         accuracy.
Certification                                                            Re-calibration is usually not necessary if:

Many of our range of volumetric products are available with              l 	 The glassware is new but been in storage for some 		
certification. Our certificates confirm that the product has been        	 time. Age does not affect accuracy.
tested for compliance to the appropriate standard. Below is an           l 	 The glassware is only subjected to moderate temperatures such 	
overview of the certification that is offered by SciLabware.             	 as cleaning in a washing machine or sterilising in an autoclave at 	
                                                                         	 121°C.
Works Certified Products                                                 l 	 The glassware has been used for less than 5 years with no 		
                                                                         	 repeated use of corrosive chemicals or strong acids/		
                                                                         	 alkalis.
                                               Pyrex® and MBL® Class
                                                                         However, recalibration should definitely be considered under the
                                               A/AS Works Certified
                                                                         following circumstances:
                                               volumetric flasks,
                                               pipettes, cylinders and   l 	 The glassware is made from soda-lime glass and has been in use 	
                                               burettes are inscribed    	 for 5 years.
                                               with an individual        l 	 The glassware is made from borosilicate and has been in use for 	
                                               serial number and         	 10 years.
                                               are supplied with an      l 	 The glassware has been subjected to temperatures in excess 	of	
                                               individual calibration    	 150°C.
                                               certificate. Each
                                                                         l 	 The glassware is frequently used with strong acids or bases.
                                               certificate includes
                                               details of the actual     l 	 There are any signs of chemical corrosion e.g. frosting of internal 	
                                               volume, uncertainty       	 glass surfaces.
                                               estimation for the
                                               calibration and the
                                               required tolerance for
                                               compliance.




                                                                                                                                                     17
Technical information - glassware

     Care and maintenance of laboratory                                                                              l We recommend that all
                                                                                                                     glassware is washed before it is
     glassware                                                                                                       first used.
     SciLabware Ltd has a commitment to provide the highest quality
     glassware products. All of our glassware is manufactured with                                                   l Wash glassware promptly after
     great care in order to provide you with a reliable piece of laboratory                                          use to avoid hard dried residues.
     equipment. To obtain maximum life and performance from your                                                     Use a biodegradable, phosphate
     glassware, correct handling is essential. The following notes will serve                                        free detergent, specially
     as a guide to new users and to remind more experienced handlers of                                              formulated for laboratory use.
     the recommended procedures.
                                                                                  l Do not use cleaning brushes which are badly worn and where the
     General precautions                                                          metal spine may scratch the glass.

     Before using any piece of glassware, take time to examine it carefully
     and ensure that it is in good condition. Do not use any glassware            Heating and cooling
     which is scratched, chipped, cracked or etched. Defects like these
                                                                                  The maximum recommended working temperature for Pyrex® and
     can seriously weaken the glass and make it
                                                                                  Quickfit® glassware is 500°C (for short periods only). However, once
     prone to breakage in use.
                                                                                  the temperature exceeds 150°C extra special care should be taken
                                                                                  to ensure that heating and cooling is achieved in a slow and uniform
     l Dispose of broken or defective glassware                                   manner.
     safely. Use a purpose-designed disposal
     bin that is puncture resistant and clearly
                                                                                  l Pyrex® borosilicate glass
     labelled.
                                                                                  is microwave safe. However,
                                                                                  as with any microwave
     l 	 Pyrex® laboratory glassware should                                       vessel, be sure it holds
     under no circumstances be disposed of in a                                   a microwave absorbing
     domestic glass recycling stream (e.g. bottle                                 material, such as water,
     banks), since its high melting point make                                    before placing in the oven.
     it incompatible with other glass (soda-lime glass) for recycling. The        Many SciLabware items
     correct method of disposal is to include it in with general waste in         utilise plastic screwcaps
     accordance with the relevant guidelines, provided that the glass is          and connectors. These are
     free of any harmful chemical contamination.                                  typically manufactured from polypropylene or PTFE, both of which are
                                                                                  microwave safe.
     l Never use excessive force to fit rubber bungs into the neck of
     glass aspirators, test tubes, conical flasks, etc. Take care to select the   l Do heat vessels gently and gradually to avoid breakage by
     correct size.                                                                thermal shock. Similarly, allow hot glassware to cool gradually and
                                                                                  in a location away from cold draughts.
     l Many SciLabware products are provided with durable, easy to use
     screwthread connectors, to allow installation of any tubing. When                                             l If you are using a hotplate,
     attaching tubing, ensure the screwthread connector is removed from                                            ensure that the top plate is larger
     the glassware, the tubing is lubricated and protective gloves are                                             than the base of the vessel to
     worn. Never use excessive force to connect rubber hose or tubing.                                             be heated. Also, never put cold
                                                                                                                   glassware onto a hotplate which
                                                                                                                   is already well heated. Warm up
                                       l Lifting or carrying large glass
                                                                                                                   gradually from ambient temperature.
                                       flasks, beakers or bottles etc. by the
                                       neck or rim can be very dangerous.
                                       It is best to provide support from the                                      l When autoclaving Pyrex®
                                       base and sides.                                                             containers, e.g. bottles with
                                                                                                                  screwcaps
                                                                                  – always slacken off the caps. Autoclaving
                                   l When stirring solutions in glass
                                                                                  with tightly screwed caps can result in
                                   vessels, such as beakers and flasks,
                                                                                  pressure differences and consequent
                                   avoid using stirring rods with sharp
                                                                                  breakage.
     ends which can scratch and weaken the glassware.

                                                                                  l If you are using a Bunsen burner,
     l Do not mix concentrated sulphuric acid with water inside a glass
                                                                                  employ a soft flame and use a wire gauze
     measuring cylinder. The heat of reaction can break the seal at the
                                                                                  with ceramic centre to diffuse the flame.
     base of the cylinder.



18
Technical information - glassware

Preparation of media                                                       	 - Carefully rock the cone in its socket to achieve separation.
                                                                           	 - If the joint is ‘dry’, try to provide lubrication. Hold the joint 		
Take great care when heating liquids that have a HIGH VISCOSITY.
                                                                           	 upright and add penetrating oil to the top of the cone. Wait until 	
Viscous liquids can act as thermal insulators and can cause ‘hot
                                                                           	 the penetrating oil is well into the joint before trying to separate.
spots’ leading to thermal breakage of the glassware. This is
particularly important with MEDIA SOLUTIONS as the viscosity usually       	   - If the use of temperature is permissible, e.g. no volatile liquids 	
increases considerably during preparation.                                 	   present, then warm the outer socket under a running stream of 	
                                                                           	   hot water from the tap. Hold under the tap for a few minutes 		
                                                                           	   before trying to separate.
                             l Do regularly stir the solution to assist
                             even distribution of heat. If using a
                             magnetic stirrer set the speed to ensure      Sintered Glassware
                             adequate agitation of the whole liquid.                           New apparatus with sintered glass discs should be
                                                                                               washed before use to remove loose particles of dust
                             l Do not use glass vessels with thick                             etc. Wash through with hot dilute hydrochloric acid
                             walls e.g. Pyrex® ‘Heavy Duty Ware’ or                            followed by a thorough rinse with water.
                             standard beakers or flasks which have
                             capacities of 5 litres or greater.
                                                                                               l Do ensure that the porosity of the sintered disc
                                                                                               is appropriate for the application. Porosity 0 sinters
Vacuum and Pressure Use                                                                        are for coarse filtration, whilst higher grades give
                                                                                               progressively finer filtration.
Because working conditions can vary enormously, SciLabware
cannot guarantee any glassware against breakage when used under
vacuum or pressure. The application of positive pressures inside                               l Never subject sintered glassware to differential
glass apparatus is particularly hazardous and should be avoided if                             pressures exceeding 100kN/m2 (1 bar).
at all possible. Safety precautions should always be taken to protect
personnel and a number of these are listed below:
                                                                           Volumetric Glassware
                                                                           Do ensure that all volumetric glassware is kept scrupulously clean.
l Always use an adequate safety
                                                                           Dirt, and especially grease, can distort the shape of the meniscus
screen and/or protective cage.
                                                                           and also cause droplets of liquid to adhere to the vessel walls. Both
                                                                           seriously impair accuracy. (Good cleanliness is indicated by uniform
l Under no circumstances use                                               wetting of the glass surface with distilled
glassware that is scratched,                                               water).
cracked or chipped. Its strength
will be seriously impaired.
                                                                           l Never pipette by mouth. Always use a
l Do not use flat bottomed vessels such as Erlenmeyer flasks and           purpose designed pipette filler.
bottles under vacuum as they are likely to implode. Exceptions are
vessels with specially thickened walls such as Büchner filter flasks and
desiccators.                                                               l Autoclaving at 121°C and cleaning in
                                                                           automatic dishwashers is acceptable and
l Avoid stress caused by over-tightening clamps. Support glassware         will not affect the accuracy of Pyrex® or
gently where possible.                                                     MBL® glassware.

l Never subject glassware to sudden pressure changes. Always                                         l All items should be held in a vertical
apply and release pressure gradients and vacuums gradually.                                          position when reading the meniscus. The
                                                                                                     meniscus should be at eye level to avoid
                                                                                                     parallax errors.
Ground Glass Joints
Lubricate the ground surfaces of joints to prevent leakage in use and                                l If using strong corrosive acids etc.
facilitate separation. Use a silicone-free laboratory grease and apply                               select volumetric ware manufactured from
a light coat completely around the upper                                                             chemically resistant
part of the joint                                                                                    Pyrex® borosilicate
                                                                                                     glass.
Alternatively, consider PTFE joint sleeves
which can be fitted between the cone
and socket.                                                                                       l Do not expose
                                                                           volumetric glassware to direct heat e.g.
                                                                           hotplates, bunsen flame.
l If ground glass joints do seize,
then the following remedies can be
considered;
	 - Always wear thick protective gloves and safety spectacles.             Pyrex® is a registered trade mark of Corning Inc.
	 Never use force.                                                         SciLabware is a registered user.


                                                                                                                                                        19

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Technical information glassware

  • 1. Technical information - glassware Glassware Chemical Composition Glass is an inorganic mixture of metal oxides fused together at high Pyrex® glass has the following typical composition (% by weight): temperatures, which upon cooling, solidifies into the clear, rigid, non- crystalline, versatile material known widely across the globe. SiO2 = 80.6% B2O3 = 13.0% Na2O = 4.0% Al2O3 = 2.3% Physical Properties Coefficient of expansion (20 – 300°C) = 3.3x10-6K-1 Density = 2.23g/cm3 Refractive index (Sodium D line) = 1.474 Dielectric constant (1MHz, 20°C) = 4.6 Specific heat (20°C) = 750J/kg°C Thermal conductivity (20°C) = 1.14W/m°C Poissons Ratio (25 - 400°C) = 0.2 Chemical Properties Pyrex® borosilicate glass has a very high resistance to attack from water, acids, salt solutions, halogens and organic solvents. Only hydrofluoric acid, hot concentrated phosphoric acid and strong alkaline solutions cause appreciable corrosion of the glass. Pyrex® Borosilicate Glass Hydrolytic resistance All Pyrex®, Quickfit®, SVL® and many MBL® branded SciLabware For many applications, it is important that laboratory glassware products are manufactured from borosilicate glass (unless otherwise has excellent hydrolytic resistance; e.g. during steam sterilisation stated). procedures, where repeated exposure to water vapour at high temperature can leach out alkali (Na+) ions. Pyrex® borosilicate glass Standards has a relatively low alkali metal oxide content and consequently a high resistance to attack from water. Pyrex® fits into Class 1 of Pyrex® is a borosilicate glass which meets the specifications of the glasses for hydrolytic resistance according to ISO 719 (98°C) and ISO following standards: 720 (121°C). ISO 3585, DIN 12217 Type 3.3 borosilicate glass Acid resistance ASTM E-438 Type 1 Class A borosilicate glass Glasses with a high percentage weight of silica (SiO2) are less likely to be attacked by acids. Pyrex® borosilicate glass is over 80% silica US Pharmacopoeia Type 1 borosilicate glass and therefore remarkably resistant to acids (with the exception of European Pharmacopoeia Type 1 glass hot concentrated phosphoric acid and hydrofluoric acid). Glass is separated into 4 acid resistance classes and Pyrex® corresponds to Due to the demanding conditions that borosilicate glass is subjected Class 1 in accordance with DIN 12116 and meets the requirements to, maximum chemical toughness, minimum thermal expansion and of ISO 1776. high resistance to thermal shock make Pyrex® the ideal material for use in the laboratory. Alkali resistance Many SciLabware Ltd products also conform to other standards set Alkaline solutions attack all glasses and Pyrex® can be classified as out for laboratory glassware; for example beakers comply to ISO moderately resistant. The alkali resistance of Pyrex® borosilicate 3819 and volumetric flasks comply to ISO 1042 and DIN 12664. glass meets Class 2 requirements as defined by ISO 695 and DIN Typically these standards will specify not only glass type, but also 52322. dimensional detail, volumetric accuracy and tolerances. 12
  • 2. Technical information - glassware Temperature resistance Glassblowing data Pyrex® borosilicate glass has excellent thermal properties at both Listed in this catalogue are some Pyrex® and Quickfit® items that are high and low temperatures. The maximum recommended working suitable for further manipulation and processing. These items include temperature for laboratory glassware manufactured from Pyrex® is stopcocks, ground glass joints, sinters and screwthreads. When 500°C (for short periods of time only). Special care should be taken working with these products, Glassblowers may find the following at temperatures above 150°C to ensure both heating and cooling are information useful regarding Pyrex® borosilicate glass: achieved in a slow and uniform manner (see Care and Maintenance of Laboratory Glassware). Working point = 1252°C Pyrex® also performs excellently at lower temperatures. Pyrex® can Softening point = 821°C withstand conditions down to approximately -192°C and is suitable Annealing point = 565°C for use with liquid nitrogen. In normal laboratory use, temperatures Strain point = 510°C of -70°C are easily sustained for lengthy periods. Again special care should be taken to avoid sudden changes in temperature, and cooling should be achieved in a slow uniform manner. Pyrex® bottles with retrace codes Pyrex® media bottles are Optical data used in many laboratory processes but they are also Pyrex® borosilicate glass is clear and colourless in appearance and used in packaging, which thus transmits light through the visible range of the spectrum. This often has to meet the quality makes it ideal for work involving photochemical reactions, strict requirements of the for example chlorinations. The graph (above) shows the degree of United States and European transmission of light as a function of wavelength in the ultra-violet, Pharmacopoeias (USP and visible and infra-red regions of the spectrum. For the majority of EP), GMP and ISO 9000. glassware detailed in our catalogue, the thickness of the glass is 2–5mm. To meet these stringent requirements, all Pyrex® 100 1-000 90 2mm 1-046 media bottles are now 80 5mm 1-097 printed with a ‘Retrace Percentage Transmission 70 1-155 Code’. This retrace code Optical Density 60 1-222 50 1-301 allows the product to 40 1-396 be traced to the point of 30 1-532 20 1-696 production and the matching batch. This code is our commitment to 10 1-699 support your quality management documentation and can be easily 0 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1 2 3 4 5 1-000 downloaded from the SciLabware web site by keying in the 8-digit Wavelength (µm) code shown on the side of the bottle. ‘Retrace’ codes can be found on all Pyrex® 1516/: 1517/: 1518/: 1519/: and 1520/: series bottles. Amber coated Pyrex® glassware Several SciLabware glass products, including media-lab bottles and volumetric flasks, are available in amber-coated glass. The glassware Pyrex® bottles with plastic coating is coated on the exterior surface with a brown diffusion colour which The Pyrex® range of 1518: media-lab bottles have a plastic coating results in a strong absorption in the short wavelength region up to to provide protection from 500nm. This feature is particularly useful when handling reagents mechanical impact and to that are light-sensitive. help reduce leakage of the contents should the glass ultraviolet range visable range infrared range 100 break. 90 The maximum working 80 temperature for these bottles 70 is 135°C but long term transmission(%) 60 exposure (>30 mins) should be avoided. 50 5000ml clear Avoid exposure to direct heat 40 500ml clear 5000ml coated from a hotplate or a Bunsen 30 flame. The 1518: media 500ml coated 20 5000ml amber bottle is suitable for freezing 10 500ml amber at -30°C and can also be 0 used in microwave ovens. 0 100 200 300 400 500 600 700 800 900 1000 1100 Please note that the plastic coating does not increase the permissible wavelength(nm) pressure at which the bottles can be used and a protective screen is recommended for all pressure work. 13
  • 3. Technical information - glassware Centrifuge tubes Sintered discs This catalogue lists a number of Pyrex® and Quickfit® centrifuge The SciLabware ranges of filtration glassware utilise sintered tubes. Within the product information for each entry we advise the discs manufactured from Pyrex® borosilicate glass. Since they are maximum Relative Centrifugal Force (RCF) they can be subjected to. manufactured from Pyrex® they are resistant to the majority of Before centrifuging, it is important to calculate the actual RCF values corrosive reagents, unaffected by ammonia, sulphuric acid and other that will be generated. This can quickly be determined by using the solvents that are damaging to filter paper. The sintered glassware is following nomogram. available in six porosity classes from 0 – 5, as outlined in the table below. The pore sizes indicated, give a range of pores present within To calculate the RCF value at any point along the tube, measure the sinter disc. Therefore, the size of particles that will be obstructed the radius, in mm, from the centre of the centrifuge spindle to the will generally be of a size at the upper end of the range. particular point. RCF Values 25,000 Porosity ISO 4793 Pore Principal 500 Grade designation index uses 20,000 475 450 (mic.) 15,000 425 400 0 P250 160 - 250 Coarse filtration, 375 350 gas dispersion 10,000 30,000 325 and support for 20,000 300 other filter material 6000 275 10,000 250 1 P160 100 - 160 Course precipitate 5000 225 filtration, gas 4000 200 dispersion, coarse 3000 2000 grain material 175 1000 filtration 2000 500 150 2 P100 40 - 100 Medium and 140 130 crystalline precipitate 200 120 filtration, medium 1000 100 110 filtration and 100 washing of gases 50 90 80 3 P40 16 - 40 Analytical work 500 20 with medium 10 70 precipitates 60 4 P16 10 - 16 Analytical work 3 with fine precipitates 200 50 5 P10 4 - 10 Bacteria filtration Speed of Relative centrifugal Radius in mm from centre of Centrifuge force (xg) centrifuge spindle to point In addition to the above detail, sinters should be treated under (rpm) along tube or bottle the same conditions as described in the general Pyrex® thermal NB: The chosen point should be the base of the tube as this area will properties as listed on page 13. experience the maximum RCF. When using new sintered glassware for the first time, we recommend Note the radius value from the right of the table and draw a line to a wash with hydrochloric acid followed by several rinses with distilled the appropriate centrifuge speed value on the left hand column. The water to remove any residual glass dust particles from the sinter. RCF value is the point where the line crosses the centre column. The nomogram is based on the following equation: RCF = (11.17x10-7) RN2 R = Rotational radius (in mm) N = Rotational speed (in RPM) The allocated RCF values are for tubes in good condition. Do not use centrifuge tubes which are scratched, abraded or chipped as the strength will be seriously impaired. 14
  • 4. Technical information - glassware Sintered discs (continued) Quickfit® Products In order to select the correct sinter for any specific application, in Conical joints addition to the porosity, it is also useful to know the flow rates of liquids and gases through the sinters. These values are given in the charts below for water and air. The data applies to 30mm diameter filter discs. The flow rates for other disc diameters can be calculated by multiplying the value read off by the conversion factor given in the table below. Filter disc dia. mm 10 20 30 40 60 90 120 150 175 Conversion factor 0,13 0,55 1 1,5 2,5 4,3 6,8 9,7 15 24/29 cone 24/29 socket Water flow rate Spherical joints S35 ball S35 cup Flat flange Screwthread 100mm bore flange 28 screwthread Dry-air flow rate Conical Joints - size designation Size Actual Actual Nominal designation dia. of wide dia. of length of end (mm) narrow engagement end (mm) (mm) 7/16 7.5 5.9 16 10/19 10.0 8.1 19 12/21 12.5 10.4 21 14/23 14.5 12.2 23 19/26 18.8 16.2 26 24/29 24.0 21.1 29 29/32 29.2 26.0 32 34/35 34.5 31.0 35 40/38 40.0 36.2 38 45/40 45.0 41.0 40 50/42 50.0 45.8 42 55/44 55.0 50.6 44 60/46 60.0 55.4 46 15
  • 5. Technical information - glassware Quickfit® screwthread joints Quickfit® flask dimensions Cap Ring Washer Volumetric Glassware Fig 1 Fig 2 SciLabware Ltd manufactures two brands of volumetric glassware, Pyrex® and MBL®. As the name indicates Pyrex® volumetrics are manufactured solely from Pyrex® borosilicate glass. MBL® volumetric products are manufactured from borosilicate and soda-lime glass. Screwcap assembly Soda-lime glass is generally used for Class B products When using screwthreads it is important that the PTFE washer is or where long term exposure to chemicals is unlikely, fitted carefully and correctly. This is best achieved by opening out e.g. one mark pipettes. the washer to the correct diameter using a tapered former. This Pyrex® volumetric glassware has superior thermal and chemical should be carried out with the silicone rubber ring and PTFE washer resistance and is better suited to glassware for storage of solutions, in position in the plastic cap as shown in Fig1. Withdraw the tapered e.g. flasks. former and remove the rubber ring and washer from the cap. The use of Pyrex® borosilicate glass for volumetric glassware means Fit each component separately to the fitting which is to be held, as accuracy is retained over a longer working lifetime than their soda- shown in Fig 2, and screw the cap on to the thread. It is advisable lime equivalents. With everyday use, volumetric glassware requires that the ends of all fittings should be slightly tapered or fired in a recalibration. Soda-lime glass items will generally necessitate twice Bunsen flame to remove sharp edges and produce a slight taper. as many recalibrations as items constructed from borosilicate glass. ASTM 542 and ISO 4787 international standards for calibration of Quickfit® flask dimensions laboratory volumetric glassware recommend that volumetric flasks are recalibrated at the following intervals (or sooner if chemical The body diameter of Quickfit® Round Bottomed and Flat Bottomed corrosion is observed): Borosilicate – 10 years; Soda-lime – 5 years. flasks comply with ISO 1773 (BS 6352). Nominal Approx Approx Nominal Approx Approx Volumetric accuracy capacity bulb bulb capacity bulb bulb SciLabware volumetric glassware is manufactured and calibrated in ml dia. ‘a’ height ‘b’ ml dia. ‘a’ height ‘b’ accordance with international ISO standards to permit very accurate mm mm mm mm determination and measurement of specific volumes. They are 5 25 - 1000 132 115 available in two accuracy classes: Class A/AS and Class B. The two classes differ in the accuracy of measurement with a Class A/AS being 10 30 - 2000 166 155 the highest accuracy, and class B is approximately half of a class A. 25 40 - 3000 188 - Class AS has the same high tolerances as Class A, but is designed to 50 50 40 5000 220 - permit more rapid outflow on burettes and pipettes. 100 65 55 10000 279 - 150 75 65 20000 345 - 250 85 75 - - - 500 105 95 - - - 16
  • 6. Technical information - glassware Inscriptions Batch certificates SciLabware volumetric glassware is manufactured and calibrated in For our ranges of Pyrex® accordance with international ISO requirements. All of our volumetric Class A volumetric glassware is marked with a set of inscriptions in accordance with any flasks and cylinders and specific standard associated with it. MBL® Class AS pipettes a downloadable batch certificate is available Tolerance Class A/AS – Highest level of accuracy. from the SciLabware Class B – General purpose work calibrated to a website. The batch lower level of accuracy certificate contains Standard The standard to which the product detailed information conforms pertaining to the specific production Graduation Pyrex® and MBL® volumetric glass is batch including average graduated in ml (millilitres) in accordance volume and standard with ISO deviation for the batch. IN Calibrated to contain To download a batch EX Calibrated to deliver certificate visit www. Blowout Indication that last drop should be blown scilabware.com and out of jet go the ‘certificates’ section then follow the links for the specified product. Simply enter the serial number marked on each volumetric Temp °C All Pyrex® and MBL® volumetric glassware item and the batch certificate is downloaded as a pdf. is calibrated at 20°C Certification All Class A/AS Works Certified glassware bears a serial number for identification Re-calibration and traceability. Normally, volumetric glassware only needs re-calibrating after extensive or demanding usage, which may have affected the original accuracy. Certification Re-calibration is usually not necessary if: Many of our range of volumetric products are available with l The glassware is new but been in storage for some certification. Our certificates confirm that the product has been time. Age does not affect accuracy. tested for compliance to the appropriate standard. Below is an l The glassware is only subjected to moderate temperatures such overview of the certification that is offered by SciLabware. as cleaning in a washing machine or sterilising in an autoclave at 121°C. Works Certified Products l The glassware has been used for less than 5 years with no repeated use of corrosive chemicals or strong acids/ alkalis. Pyrex® and MBL® Class However, recalibration should definitely be considered under the A/AS Works Certified following circumstances: volumetric flasks, pipettes, cylinders and l The glassware is made from soda-lime glass and has been in use burettes are inscribed for 5 years. with an individual l The glassware is made from borosilicate and has been in use for serial number and 10 years. are supplied with an l The glassware has been subjected to temperatures in excess of individual calibration 150°C. certificate. Each l The glassware is frequently used with strong acids or bases. certificate includes details of the actual l There are any signs of chemical corrosion e.g. frosting of internal volume, uncertainty glass surfaces. estimation for the calibration and the required tolerance for compliance. 17
  • 7. Technical information - glassware Care and maintenance of laboratory l We recommend that all glassware is washed before it is glassware first used. SciLabware Ltd has a commitment to provide the highest quality glassware products. All of our glassware is manufactured with l Wash glassware promptly after great care in order to provide you with a reliable piece of laboratory use to avoid hard dried residues. equipment. To obtain maximum life and performance from your Use a biodegradable, phosphate glassware, correct handling is essential. The following notes will serve free detergent, specially as a guide to new users and to remind more experienced handlers of formulated for laboratory use. the recommended procedures. l Do not use cleaning brushes which are badly worn and where the General precautions metal spine may scratch the glass. Before using any piece of glassware, take time to examine it carefully and ensure that it is in good condition. Do not use any glassware Heating and cooling which is scratched, chipped, cracked or etched. Defects like these The maximum recommended working temperature for Pyrex® and can seriously weaken the glass and make it Quickfit® glassware is 500°C (for short periods only). However, once prone to breakage in use. the temperature exceeds 150°C extra special care should be taken to ensure that heating and cooling is achieved in a slow and uniform l Dispose of broken or defective glassware manner. safely. Use a purpose-designed disposal bin that is puncture resistant and clearly l Pyrex® borosilicate glass labelled. is microwave safe. However, as with any microwave l Pyrex® laboratory glassware should vessel, be sure it holds under no circumstances be disposed of in a a microwave absorbing domestic glass recycling stream (e.g. bottle material, such as water, banks), since its high melting point make before placing in the oven. it incompatible with other glass (soda-lime glass) for recycling. The Many SciLabware items correct method of disposal is to include it in with general waste in utilise plastic screwcaps accordance with the relevant guidelines, provided that the glass is and connectors. These are free of any harmful chemical contamination. typically manufactured from polypropylene or PTFE, both of which are microwave safe. l Never use excessive force to fit rubber bungs into the neck of glass aspirators, test tubes, conical flasks, etc. Take care to select the l Do heat vessels gently and gradually to avoid breakage by correct size. thermal shock. Similarly, allow hot glassware to cool gradually and in a location away from cold draughts. l Many SciLabware products are provided with durable, easy to use screwthread connectors, to allow installation of any tubing. When l If you are using a hotplate, attaching tubing, ensure the screwthread connector is removed from ensure that the top plate is larger the glassware, the tubing is lubricated and protective gloves are than the base of the vessel to worn. Never use excessive force to connect rubber hose or tubing. be heated. Also, never put cold glassware onto a hotplate which is already well heated. Warm up l Lifting or carrying large glass gradually from ambient temperature. flasks, beakers or bottles etc. by the neck or rim can be very dangerous. It is best to provide support from the l When autoclaving Pyrex® base and sides. containers, e.g. bottles with screwcaps – always slacken off the caps. Autoclaving l When stirring solutions in glass with tightly screwed caps can result in vessels, such as beakers and flasks, pressure differences and consequent avoid using stirring rods with sharp breakage. ends which can scratch and weaken the glassware. l If you are using a Bunsen burner, l Do not mix concentrated sulphuric acid with water inside a glass employ a soft flame and use a wire gauze measuring cylinder. The heat of reaction can break the seal at the with ceramic centre to diffuse the flame. base of the cylinder. 18
  • 8. Technical information - glassware Preparation of media - Carefully rock the cone in its socket to achieve separation. - If the joint is ‘dry’, try to provide lubrication. Hold the joint Take great care when heating liquids that have a HIGH VISCOSITY. upright and add penetrating oil to the top of the cone. Wait until Viscous liquids can act as thermal insulators and can cause ‘hot the penetrating oil is well into the joint before trying to separate. spots’ leading to thermal breakage of the glassware. This is particularly important with MEDIA SOLUTIONS as the viscosity usually - If the use of temperature is permissible, e.g. no volatile liquids increases considerably during preparation. present, then warm the outer socket under a running stream of hot water from the tap. Hold under the tap for a few minutes before trying to separate. l Do regularly stir the solution to assist even distribution of heat. If using a magnetic stirrer set the speed to ensure Sintered Glassware adequate agitation of the whole liquid. New apparatus with sintered glass discs should be washed before use to remove loose particles of dust l Do not use glass vessels with thick etc. Wash through with hot dilute hydrochloric acid walls e.g. Pyrex® ‘Heavy Duty Ware’ or followed by a thorough rinse with water. standard beakers or flasks which have capacities of 5 litres or greater. l Do ensure that the porosity of the sintered disc is appropriate for the application. Porosity 0 sinters Vacuum and Pressure Use are for coarse filtration, whilst higher grades give progressively finer filtration. Because working conditions can vary enormously, SciLabware cannot guarantee any glassware against breakage when used under vacuum or pressure. The application of positive pressures inside l Never subject sintered glassware to differential glass apparatus is particularly hazardous and should be avoided if pressures exceeding 100kN/m2 (1 bar). at all possible. Safety precautions should always be taken to protect personnel and a number of these are listed below: Volumetric Glassware Do ensure that all volumetric glassware is kept scrupulously clean. l Always use an adequate safety Dirt, and especially grease, can distort the shape of the meniscus screen and/or protective cage. and also cause droplets of liquid to adhere to the vessel walls. Both seriously impair accuracy. (Good cleanliness is indicated by uniform l Under no circumstances use wetting of the glass surface with distilled glassware that is scratched, water). cracked or chipped. Its strength will be seriously impaired. l Never pipette by mouth. Always use a l Do not use flat bottomed vessels such as Erlenmeyer flasks and purpose designed pipette filler. bottles under vacuum as they are likely to implode. Exceptions are vessels with specially thickened walls such as Büchner filter flasks and desiccators. l Autoclaving at 121°C and cleaning in automatic dishwashers is acceptable and l Avoid stress caused by over-tightening clamps. Support glassware will not affect the accuracy of Pyrex® or gently where possible. MBL® glassware. l Never subject glassware to sudden pressure changes. Always l All items should be held in a vertical apply and release pressure gradients and vacuums gradually. position when reading the meniscus. The meniscus should be at eye level to avoid parallax errors. Ground Glass Joints Lubricate the ground surfaces of joints to prevent leakage in use and l If using strong corrosive acids etc. facilitate separation. Use a silicone-free laboratory grease and apply select volumetric ware manufactured from a light coat completely around the upper chemically resistant part of the joint Pyrex® borosilicate glass. Alternatively, consider PTFE joint sleeves which can be fitted between the cone and socket. l Do not expose volumetric glassware to direct heat e.g. hotplates, bunsen flame. l If ground glass joints do seize, then the following remedies can be considered; - Always wear thick protective gloves and safety spectacles. Pyrex® is a registered trade mark of Corning Inc. Never use force. SciLabware is a registered user. 19