68 Proceedings of Philosophical Societies. [July, 



ments made to ascertain the effects of voltaic electricity upon 

 vegetable life, by J. Williams, Esq. 



June 11. — A paper, by Dr. Prout, was read, on a new acid 

 principle prepared from lithic or uric acid. The beautiful purple 

 substance produced by the action of nitric acid and heat upon 

 lithic acid has been long known to chemists. This substance 

 Dr. P. has shown to be a compound of a peculiar acid with 

 ammonia. 



This acid principle, which may be likewise formed from the 

 lithic acid by chlorine and iodine, possesses the remarkable 

 property of forming beautiful purple compounds with the alkalies 

 and alkaline earths ; hence the name of purpuric acid has been 

 adopted by Dr. P. which was suggested by Dr. Wollaston. 



Purpuric acid may be separated from the purpuret of ammonia, 

 before mentioned, by the sulphuric or muriatic acids. It usually 

 exists in the form of a light yellow or cream-coloured powder. 

 It is exceedingly insoluble in water, and consequently possesses 

 no taste, nor affects litmus paper, though it readily decomposes 

 the alkaline carbonates by the assistance of heat. It is soluble 

 in the strong mineral acids and in alkaline solutions, but not in 

 dilute acids in general. In alcohol, it is insoluble. When 

 exposed to the air, it assumes a purple colour, probably by 

 attracting ammonia. Submitted to neat, it is decomposed, and 

 yields carbonate of ammonia, prussic acid, and a little fluid of 

 an oily appearance. Burned with the oxide of copper, it was 

 found to consist of 



Hydrogen 4*54 



Carbon 27-27 



Oxygen 36-36 



Azote 31-81 



The alkaline purpurates, as before observed, all form solutions 

 of a beautiful purple colour. They are capable of crystallizing, 

 and their crystals possess so-oie remarkable properties. The 

 purpurate of ammonia crystallizes in quadrangular prisms, which, 

 when viewed by transmitted light, appear of a deep garnet red ; 

 but by reflected light, two of the opposite surfaces appear of a beau- 

 tiful green, while the other two opposite surfaces appear of the 

 natural colour. This curious property seems to be possessed by 

 the other alkaline purpurates. The metallic purpurates are, in 

 general, remarkable for their solubility and the beauty of their 

 colours. The purpurate of zinc is of a beautiful gold yellow, the 

 purpurate of tin of a pearly white, that of the other puq^mates 

 are more or less of a red colour. 



Dr. P. thinks it probable that this acid forms the basis of 

 many animal and vegetable colours. The pink colour of the 

 sediment in the urine of fever seems to be owing to the purpu- 

 rate of ammonia. Dr. P. also thinks that some of its salts might 

 be used as paints, and also for dyeing, as they appear to possess 

 strong affinities, especially for animal substances. 



