C 420 3 
XXII. Description of an acid principle prepared from the lithic 
or uric acid. By William Prout, M. D. Communicated by 
W. H. Wollaston, M. D . F. R. S. 
Read June 11, 1818. 
During an investigation of the principles of the urine, with 
the view of elucidating the pathology of that secretion, I was 
led to examine the well-known beautiful purple substance 
produced by the action of the nitric acid and heat upon the 
lithic acid, and which has usually been considered as one of 
the characteristic distinctions of the lithic acid. This purple 
substance proved to be a compound of ammonia, and a pecu- 
liar principle having the properties of an acid ; the description 
of which, and of its compounds, constitutes the object of the 
present paper. 
This acid principle may be obtained by digesting pure 
lithic acid in dilute nitric acid : an effervescence takes place, 
and the lithic acid is dissolved. The excess of nitric acid is 
then to be neutralized with ammonia, and the whole slowly 
concentrated by evaporation. As the evaporation proceeds, 
the colour of the solution gradually becomes of a deeper 
purple, and dark red granular crystals (sometimes of a 
greenish hue externally) soon begin to separate in abun- 
dance. These crystals are a compound of ammonia with the 
acid principle in question. The ammonia may be removed 
by the sulphuric or muriatic acid, and thus the acid principle 
obtained in a~ separate state. As, however, I found some 
