Borosilicate glass

This is better known by its trade name of Pyrex. It is more expensive than the cheaper soda glass, but is better suited for chemical apparatus. It has a higher melting point so can be used where relatively strong heating is required. It is also much better at coping with thermal shock. If hot glass is cooled suddenly by putting it into cold water it may crack or shatter. Pyrex copes relatively well with rapid cooling. If you have been boiling an aqueous solution then the temperature will be around 100 °C. This can be cooled straight away under cold water with little danger of cracking (you will, of course, be wearing eye protection anyway).

Pyrex glassware

There are limits to the ability of borosilicate glass, though. If you are heating a solid in a test tube the temperature may have reached several hundred degrees centigrade. Trying to cool this immediately in cold water may well lead to it shattering. See the section on suck back. When your test tube is very hot it should be placed on a heat-proof mat for a few minutes so that it can cool to a safer temperature. Make sure that no-one touches it during this cooling period. Don't put your hot test tube onto the bench or into a test tube rack they will burn or melt! With plastic test tube racks the test tubes can become welded to the plastic - you will not be popular with your teacher or technician!