Lond. Chlorate of Potassa.

This salt is made by passing a stream of chlorine through a concentrated solution of pure potassa until the alkali is completely neutralized. In this case, the potassa is decomposed, and the oxygen of five equivalents combining with one equivalent of chlorine, form the chloric acid, which uniting with the undecomposed potassa forms the chlorate of that salt; whilst the five equivalents of potassium set free combining with five equivalents of chlorine, form the chloride. The solution is then boiled for a few minutes to expel any excess of chlorine, and allowed to cool. In this state it contains both chloride of potassium and chlorate of potassa; but, as the latter is much less soluble than the former, the chlorate crystallizes, whilst the chloride still remains in solution. The crystals, thus procured, require to be washed in cold water and recrystallized.

1 The value of the diluted acid must be previously ascertained, by adding to 100 grains of it chloride of barium as long as any precipitate falls. This forms sulphate of baryta, which, when washed, and dried at a low red heat, contains 33.3 per cent, of sulphuric acid; by which the proportion of real acid in the diluted acid may be known,-Aikin's Dictionary, i. 263.

Qualities.-Chlorate of potassa is an inodorous white salt of a pearly lustre : its taste is cool and austere : it crystallizes in four and six sided scales, which require sixteen parts of water at 60°, and two and a half at 212°, for their solution. At a temperature of 400° to 500° it undergoes the igneous fusion; and at 666° it is decomposed, and pure oxygen gas is disengaged. It contains no water of crystallization. It is a compound of 61.228 parts of chloric acid + 38.772 of potassa in 100 parts; or 1 equiv. chloric acid = 75.42 +1 potassa = 47.15, making the equiv. = 112.67.

Medical properties and uses.-Chlorate of potassa is a stimulant tonic. It is little employed; but it may be advantageously prescribed to rouse the energies of the system in typhus and other depressing affections. It was at one time employed in the treatment of syphilis, but it has deservedly fallen into disrepute in that disease. The dose of the salt is from grs. vj. to Э j. in solution, three times a day.