It is recommended that this acid should be prepared by the user himself, the cost in this case being 7s. to 9s. a lb., whereas the manufacturers demand 40?. It can be prepared in the following manner without the slightest danger: - Pure barium chlorate is dissolved in lukewarm water, and dilute sulphuric acid is added. The precipitate is allowed to settle, the clear liquid is poured off, and the barium sulphate is thoroughly washed. The chloric acid solution is then evaporated over a fire until the concentrated solution becomes yellow, and on further evaporation produces a peculiar noise. The liquid is divided into two parts, placed in two dishes 6 in. wide, and containing about 175 fl. dr., and evaporated further until the liquid is quite decolorized and thick white fumes are given off. In order to lessen this unavoidable loss of perchloric acid, the liquid can be diluted from time to time with a little water. The colourless liquid is then distilled in a retort heated on a sand-bath, and collected in a long-necked receiver.

The perchloric acid so obtained contains traces of iron. (Monti, Scient.)