prepared from the Lithic or Uric Acid. 27 
a portion of the purpuric acid is decomposed, ammonia is formed; 
and on driving off the excess of nitric acid by heat, the purpurate 
of ammonia is obtained, precisely as if a little of the lithic acid 
" had been treated in a similar manner. Chlorine, likewise, dis- 
solves the purpuric acid, and apparently produces the same 
changes upon it as the nitric acid. It readily dissolves also by 
the assistance of heat, in concentrated acetic acid. 
The purpuric acid does not sensibly affect litmus paper, pro- - 
bably on account of its insoluble nature. When exposed to the 
air it does not deliquesce, but gradually assumes a purplish tint, 
apparently by attracting a little ammonia from the atmosphere, 
or perhaps from the evolution from itself of a little of the same 
alkali by spontaneous decomposition, 
Submitted to heat, it neither melts nor sublimes, but acquires 
a purple hue from the formation of ammonia, and afterwards 
burns gradually, without yielding any remarkable odour. Sub- 
jected alone to heat in close vessels, it yields a considerable pro- 
portion of the carbonate of ammunia, some. prussic acid, and a 
little fluid having an oily appearance; while a portion of pulveru- 
lent charcoal remains. When given quantities were burnt with 
the oxide of copper, in the manner formerly described by me *, 
data were obtained, which appeared to show that one hundred 
parts consist of 
Hydrogen 4°54 corresponding with 2 atoms or proportions. 
Garbonieh BWHB7s 3). ko Sool ys ele Ditto 
Oxygen 36°36 .....ceeeeeeees. 2 ditto 
Azote GST "sii e's bs Swe apis een PRO 
The purpuric acid combines with the alkalies, alkaline earths, 
aud metallic oxides. It is capable of expelling the carbonic acid 
from the alkaline carbonates, by the assistance of heat, and does 
not, as far as I have observed, combine with any other acid. 
These are circumstances sufficient, as Dr, Wollaston has observed, 
to distinguish it from an oxide, and to establish its character as 
an acid. On the supposition then, that it be named the purpu- 
ric acid, its compounds with different bases must be denominated 
purpurates: on some of the most remarkable of which I shall 
now proceed to make a few remarks. 
Purpurate of ammonia. This salt crystallizes in quadrangular 
prisms, which, when viewed by transmitted light, are transparent, 
and of a deep garnet red colour; but by reflected light, their two 
broadest opposite faces appear of a brilliant green, closely resem- 
bling that of the wings of some of the beetle tribe, as for exam- 
ple, of the Cetonia aurata, while their other two opposite faces 
appear of adull reddish brown colour; or, if the light be very 
strong, slightly green. This peculiarity seems to be possessed 
* See Medico-Chirurgical Transactions, vol. viii. p. 526. : 
in 
