TECHNICAL INFORMATION
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Care and Handling of Glassware
Care and Use — Ground-Glass Surfaces Ground-glass joints and stopcocks should never be used when dry. Although ground-glass surfaces seal well without the use of lubricants, it is advisable to lubricate them to prevent sticking and breakage. Ground surfaces must be cleaned prior to lubrication— dust, dirt, and particulate matter may score the surface and cause leakage. Different lubricants are used for these operating conditions: Silicone grease—for high temperature and high vacuum Glycerin—for long term reflux or extraction Hydrocarbon grease—for general laboratory use Lubricating Ground-Glass Joints 1. Lubricate joints that must be airtight and when glassware contains strong alkaline solutions. 2. Lubricate only the upper part of the inner joint. A properly lubricated joint appears clear, without striations. 3. Do not allow grease to come in contact with vapor or liquid and cause contamination. Lubricating Stopcocks Spread two circular bands of grease around the stopcock plug. Insert the plug into the barrel and twist several times until the assembly is completely transparent. Be careful not to use too much lubricant or the bore will become plugged. Care and Use — HI-VAC ® PTFE VALVES 1. Valves are assembled with FKM O-rings, suitable for use with oxidizing and NON-POLAR compounds at temperatures from -23 °C to 204 °C. 2. All elastomers have outgassing rates higher than glass. Long pump-down periods will typically reduce these rates by a factor of ten. Vacuum systems using PTFE valves normally operate at pressures up to 10 -6 mm Hg. Heating of this valve during pump- down with an air heat gun will improve ultimate vacuum. 3. O-rings should be lubricated with a thin film of vacuum grease to prolong life and reduce leakage by allowing the o-ring to slip easily along the tube. Excess grease should be thoroughly wiped off. 4. Any leakage across the o-ring stem seal occurs mainly on the inward movement. Turning the stem in and out during pump-down helps evacuate the space between the two stem o-rings. One o-ring may be removed if preferred, improving performance under some conditions. 5. O-rings may be removed from the stem by pushing the o-ring into the groove with thumb and forefinger, distorting ring sufficiently to form a small loop which can be “picked up” and the o-ring pulled off of the stem without damaging surfaces.
Care and Use — Stopcocks with Plugs Made of Polytetrafluoroethylene (PTFE) Kimble® stopcock plugs of PTFE are made of the most chemically inert material in laboratory use today. Only a few chemicals have any effect on PTFE and these only at elevated temperatures and pressures. The material is extremely tough, durable, and heat resistant, with practically zero moisture-absorption. It remains non-brittle even at sub-zero temperatures. To obtain maximum performance from your stopcock plugs of PTFE, observe the following hints: 1. To clean new plugs, carefully disassemble, lift plug free of glass barrel, and rinse all parts of plug and barrel in acetone. After drying, reassemble and the stopcock is ready for use. (Do not use abrasive materials to clean either plug or barrel at any time.) 2. The washer of PTFE must always be placed adjacent to the end of the glass barrel, to secure minimal friction when turning. When properly tightened, the plug will be slightly more resistant to turning than a lubricated glass plug. 3. Plugs of PTFE can be easily scored around the bore if rotated when solid particles are lodged between plug and barrel or project beyond mating edges of glass parts. Once scored, the plug may leak. 4. Do not use a stopcock plug of PTFE on a vessel used for long-time storage of liquids known to attack glass, since the surface of the barrel may become roughened and leakage may occur between the plug and and barrel, causing a potential safety hazard. 5. If plugs of PTFE are used with liquids corrosive to glass, such as alkalies, rinse the stopcock thoroughly with water after use. Do not allow the liquid to evaporate. The concentrated solution remaining will attack the glass surface, and the eventual solids may also mar the surface of PTFE if the plug is then rotated. 6. When not in use, store in a dust-free area with plug loosened within the glass barrel Although tough and unbreakable, PTFE is softer than glass and has a tendency to conform to the glass surface, including eventual expansion into the hollow parts of the barrel.
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