COMMON LABORATORY
TECHNIQUES AND
PRACTICES

Cleaning Glassware A common laboratory requirement is clean glassware. If clean, the walls will retain an unbroken film of water, not droplets. This can usually be achieved most simply and safely by scrubbing the wet walls with some common commercial scouring powder and an appropriate brush, followed by rinsing with tap water and finally with distilled water. Never use scouring powder on glassware which is inaccessible to scrubbing such as the inside of a transfer pipet. For this type of glassware use a liquid detergent in place of the scouring powder. Occasionally, specific chemical deposits are completely unaffected by these general cleaning methods, but if the chemical nature of the deposit is known, a specific reagent may be selected for cleaning; ask your instructor for advice in this circumstance.

Drying Operations Glassware must frequently be dry as well as clean. This is best done by putting the glassware into a drying oven, preferably one with circulating air that will quickly remove the water vapor. Hot glassware with parallel sides, such as beakers and bottles, is most conveniently handled with beaker tongs as shown in Fig. 2. It is unwise to dry Pyrex and Kimax equipment by direct heating with a Bunsen burner; it is usually fatal (to the glassware) to treat soft glass equipment this way. Alternatives to the drying oven are wiping with clean toweling (but cloth and paper lint are often a problem), or rinsing with volatile acetone followed by drawing clean air through the container; however, acetone is rather expensive and highly flammable. A common requirement, especially in quantitative analysis, is a very dry sample or product. These materials are usually dried in the drying oven at a specified temperature for a specified length of time, followed by immediate transfer to a