sIviii Historical Sketch of the Physical Sciences, 1818. 
caustic potash, and heat applied to the solution till the red 
colour entirely disappears. Drop the alkaline solution into di- 
tute sulphuric acid, the purpuric acid separates in a state of purity. 
_ Purpuric acid, thus obtained, is a cream-coloured powder, 
destitute of taste and smell. It is scarcely soluble in water, and 
not soluble in alcohol or ether. It dissolves in the concentrated 
mineral acids, but not in these acids when in a state of dilution, 
nor in solutions of oxalic, citric, and tartaric acid. Concentrated 
nitric acid dissolves it with effervescence, and if heat be applied, 
purpurate of ammonia is formed. Chlorine produces the same 
changes as nitric acid. It dissolves im concentrated acetic acid 
when assisted by heat. 
It does not redden litmus paper, does not attract moisture 
from the atmosphere; but assumes a reddish colour, and is 
apparently converted into purpurate of ammonia. When heated, 
it neither melts nor sublimes, but acquires a purple colour, and 
then burns away without yielding any remarkable odour. When 
distilled, it yields carbonate of ammonia, a little prussic acid, 
and an oily looking fluid, while a pulverulent charcoal remains 
behind. Its constituents, as determined by heating it with 
peroxide of copper, were as follows : 
2 atoms hydrogen. ....6....s0008 % 0°25 
> atonis ‘Carbon . ss st 44 SOPH, ATS oe 150 
Zatorms oxygen. Se. J VNEe 12-06 
} atom. azote’s tue Bl. ee Ca Sle 
5:00 
If this analysis be correct, the weight of an atom of purpurie 
acid is precisely the same with that of an atom of sulphuric 
acid ; consequently the constitution of the sulphates and purpu- 
rates willbe the same. This would require to be determined by 
analysis, before we can have any precise notion of the weight of 
an atom of purpuric acid. 
Most of the purpurates have a red colour. Purpurate of 
ammonia crystallizes in four-sided prisms, which by transmitted 
light are deep garnet red, but by reflected light appear of a bmil- 
liant green. Most of the other purpurates possess the same 
peculiarity. Purpurate of ammonia is soluble in about 1500 
times its weight of water at 6U°, but it is much more soluble in 
hot water. ‘Ihe solution has a slightly sweetish taste, no smell, 
and a fire crimson colour. Purpurates of potash and of mag- 
nesia are much more soluble than purpurate of ammonia or 
purpurate of soda. Purpurate of lime resembles in colour the 
’ erust of the lobster before boiling. Purpurates of lime, barytes, 
strontian, alumina, silver, and mercury, seem to be least soluble ; 
while purpurates of gold, platinum, lead, zinc, tin, copper, 
nickel, cobalt, and iron, are most soluble.—-(See Phil. Tians. 
1818, p, 240.) 
