PURPURIC Aein, is the name of a new acid, re cently discovered by that able chemist Dr. Prout. It has long been known to chemists that a fine purple liquid is produced by the action of heat and nitric acid upon lithic acid.* When the excess of nitric acid is neutralised by ammonia, and the whole concentrated by slow evaporation, granular crystals of a dark red colour, and sometimes of a greenish hue, are formed. These crystals are the pur purate of ammonia. In order to obtain the purpuric acid, digest the crystals in a solution of caustic potash till the red colour disappears, and drop the alkaline solution by degrees into sulphuric acid, which unites with the potash, and leaves the purpuric acid in the form of a light yellow, or cream coloured powder. It is insoluble in alcohol and ether, and very insoluble in water. It has no taste nor smell. The specific gravity is greater than that of water, It is dissolved by the mineral acids when they are con centrated. According to Dr. Prout, its composition is as follows : Purpuric acid may be obtained from lithic acid by chlorine, and with more difficulty from iodine.
The Purpurate of ammonia crystallizes in quadrangular prisms, of a deep garnet red colour, by transmitted light ; but, by reflected light, their two broadest faces appear of a brilliant green, while their other two faces appear of a dull reddish-brown colour. The purpuric acid forms other neutral salts with potash, lime, magnesia, stronnan, alu mina, and almost all the metals. Dr. Prout considers the salts as anhydrous, and composed of two atoms of acid and one of base. He conceives that the purpuric acid and its compounds may constitute the basis of many animal and vegetable colours. He remarks, that " some of the pur purates, as, for example, that of lime, might be probably used as a paint. They might be also used for dyeing, especially wool and other animal productions." See Philo sophical Transactions for 1818, p. 420.