Chromium Compounds
Working Safely

We use two chromium compounds for fixation. They are chromium trioxide, which produces chromic acid when dissolved in water, and potassium dichromate. Potassium dichromate is reasonably safe to handle and easy to work with and presents few problems. It should be handled with the same care as any other chemical in a laboratory.

Chromium trioxide is another matter as when it is dissolved in water it forms a strong acid (chromic acid). This acid used to be used for cleaning glassware in the past, although the cleaning solution was made by adding sulphuric acid to potassium dichromate solutions. It was considered to be the ultimate cleaner, removing just about all known materials. If glassware could not be cleaned with chromic acid it was usually discarded as being beyond recovery.

Just a few granules of the dry chemical will discolour the skin, even when washed off immediately. This emphasises how much caution needs to be taken to ensure that skin is not contaminated with dry chemical or solutions of this acid. It is a strong oxidising agent and must be handled and stored with some care. The crystals give off corrosive fumes, and this has to be taken into account when storing the chemical. It should not be stored close to reducing agents, or with chemicals that are easily oxidised into other compounds.

If the dry chemical is spilled, the first step is to put on protective gloves and an apron for safety. The excess dry chemical may then be scooped into a plastic or glass container. Finally, the area should be washed down with a cloth or towels and copious amounts of water. Before doing so ensure that all objects are removed so that no dry chemical is trapped under them. All contaminated material should be disposed of according to local regulations.




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