Page 131 - The Veterinary Laboratory and Field Manual 3rd Edition

100 Willy Schauwers

• Pyrex borosilicate glass is microwave safe. Vacuum and pressure use
However, as with any microwave vessel, be
sure it holds a microwave absorbing mate- • The application of positive pressures inside
rial, such as water, before placing in the glass apparatus is particularly hazardous
oven. Plastic screwcaps and connectors man- and should be avoided if at all possible.
ufactured from polypropylene or PTFE, are Safety precautions should always be taken to
microwave safe. protect personnel.
• Heat vessels gently and gradually to avoid • If necessary, always use an adequate safety
breakage by thermal shock. Similarly, allow screen and/or protective cage.
hot glassware to cool gradually and in a loca- • Under no circumstances use glassware that
tion away from cold draughts. is scratched, cracked or chipped. Its strength
• If you are using a hotplate, ensure that the will be seriously impaired.
top plate is larger than the base of the vessel • Do not use flat bottomed vessels, such as
to be heated. Also, never put cold glassware Erlenmeyer flasks and bottles, under vacuum
onto a hotplate which is already well heated. as they are likely to implode. Exceptions are
Warm up gradually from ambient tempera- vessels with specially thickened walls such as
ture. Büchner filter flasks and desiccators.
• When autoclaving Pyrex containers, for • Avoid stress caused by over-tightening clamps.
example, bottles with screwcaps – always Support glassware gently where possible.
slacken off the caps. Autoclaving with tightly • Never subject glassware to sudden pressure
screwed caps can result in pressure differ- changes. Always apply and release pressure
ences and consequent breakage. gradients and vacuums gradually.
• If you are using a Bunsen burner, employ a
soft flame and use a wire gauze with ceramic
centre to diffuse the flame. care and maintenance of laboratory
plastic ware

Preparation of media General precautions

• Take great care when heating liquids that have The following guidelines are provided to ensure
a high viscosity. Viscous liquids can act as your plastic laboratory-ware is maintained in the
thermal insulators and can cause ‘hot spots’ best possible condition. These guidelines are
leading to thermal breakage of the glassware. not definitive and care must be taken as each
This is particularly important with media polymer has its own unique properties.
solutions as the viscosity usually increases Chemicals can adversely affect the perfor-
considerably during preparation. mance of laboratory plastic ware resulting in
• Regularly stir the solution to assist even dis- cracking, loss of strength and flexibility. If
tribution of heat. If using a magnetic stirrer in any doubt, note the type of polymer the prod-
set the speed to ensure adequate agitation of uct is manufactured from, the chemical that is to
the whole liquid. be used, then confirm compatibility by checking
• Do not use glass vessels with thick walls, for against a chemical resistance chart.
example, ‘heavy duty ware’ or standard bea-
kers or flasks which have capacities of 5 l or HEatInG
greater. • Never place plastic ware in direct contact
with a flame or place onto a hotplate surface.

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