The last mentioned compound may be removed by evaporating successively with hydrochloric acid and water. If the platinic chlorid be made from waste platinum, the danger of contamination with iridium must be considered. In such a case the platinum should be separated as ammonium platinochlorid, which can afterwards be reduced as above indicated. A convenient test of the purity of platinic chlorid solution is accomplished by the precipitation of a known weight of chemically pure potassium salt. (2) _By Reduction in Nascent Hydrogen._—The platinum residues, filtrates containing platinum, etc., are collected in a large flask and evaporated in a large dish on a water-bath, and reduced by means of zinc and hydrochloric acid to metallic platinum, the mass being warmed until all the zinc has been dissolved. The supernatant liquid standing over the spongy platinum is decanted and the spongy mass boiled twice with distilled water. The spongy platinum is then brought on a filter and washed till the filtrate shows no acid reaction. The filter and platinum sponge are next incinerated in a platinum dish and the residue weighed. The weighed mass of pure platinum is dissolved in hydrochloric acid, with the addition of as little nitric acid as possible, and, after cooling, filtered. The filtrate is afterwards evaporated in a porcelain dish on a water-bath to a sirupy consistence, taken up with water and filtered. To this filtrate enough water is now added to make the solution correspond to one gram of metallic platinum in ten cubic centimeters. THE ESTIMATION OF POTASH AS PERCHLORATE.