Chromium

Chromium compounds are used extensively in histotechnology. Their use goes back to the early days of microtechnique, when potassium dichromate was used as a hardening agent so that thin slices could be cut. This practice led to it's use as a fixing agent, which still continues in Zenker's, Helly's and similar fixatives. A simple solution is sometimes used for post-chroming, a method of fixing lipids, and important in the demonstration of mitochondria.

An aqueous solution of chromium trioxide (chromic acid) is a strong oxidising agent used to form aldehydes from polysaccharides in Bauer’s stain, originally recommended for demonstrating glycogen, but also suitable for demonstrating fungi.

Chromic acid is also made from potassium dichromate and sulphuric acid. This is a traditional and very effective cleaning solution for glassware which removes all traces of just about everything. It must be used with care as it will burn the skin if gloves and other protective clothing are not worn.

Chrome alum (chromium potassium sulphate) is used to mordant gallocyanin in Einarson’s method for nucleic acids. It has also been used with hematein. Chrome mordants were important in textile dyeing in the past, although less so today. The terms "onchrome", "metachrome" and "afterchrome" are derived from this use, referring to the sequence in which the mordant was applied with respect to the dye, (before, during and after, respectively).

 


 

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