prepared from the lithic or uric acid. 4,27 
Purpurate of copper. A solution of the acetate or sulphate of 
copper changes the purpurate of ammonia to a bright yellowish 
green colour, but produces no precipitation. 
Purpurate of nickel. The nitrate of nickel imparts to the 
purpurate of ammonia a greenish tinge, but produces no 
precipitation. 
Purpurate of cobalt. The acetate of cobalt changes the 
colour of the same salt to a pale scarlet. After some time, 
reddish granular crystals form, which are the purpurate of 
cobalt. 
Purpurate of iron. A solution of the green sulphate of iron 
changes the colour of the purpurate of ammonia to yellowish 
red, but produces no precipitate. 
Such is a very brief account of the purpurates t as far as I 
have examined them. It may at first sight appear singular, 
that such an insoluble acid should form so many soluble 
compounds ; but when we reflect upon the subject, and con- 
sider what a very small quantity of the purpurate of ammonia 
is retained in solution by water, and that this small quantity 
has been made the standard of comparison in the above 
experiments, our surprize is considerably lessened, and we 
feel no difficulty in conceiving, that if the purpurates were 
compared with the nitrates, for example, the former would 
be found by far the least soluble. 
From the very small quantities on which I have been 
obliged to operate, and from other circumstances, I can 
offer but little respecting the constitution of the purpu- 
rates. Those which I have attempted to analyze appear 
to be anhydrous, and to be composed of two atoms of 
the acid, and one of the base ; and if this be correct, the 
MBCCCXVIII. 3 K 
