Recycling procedure for gold chloride used in neurohistology.

A simple method is described whereby pure chloroauric acid (HAuCl4; "brown gold chloride") is recovered from old solutions used for toning silver-stained sections. The procedure can be carried out in any laboratory and 60 to 80% of the gold initially present in a solution is recovered. The recycled product may be used for toning or for the staining of astrocytes by Cajal's method.