175 
time; but as the results of the few experiments which I made 
with phosphoric and sulphuric acid on the p. carminate and 
¢. carminate were so unsatisfactory, I did not continue them, and 
did not very carefully examine the products to which they gave 
rise. 
From these experiments I infer, first that two distinct colouring 
matters exist in cochineal, the c. carminic acid and the p. car- 
minic acid. That the first is extremely unstable and easily de- 
composed by heat and strong acids and even ammonia, the 
result of the decomposition being in part the second acid. For 
I succeeded in obtaining p. carminate of lead of the bluest tint 
most free from any c. carminate by boiling, for an hour or two, 
cochineal in water, adding acetic acid to the decoction and filter- 
ing, neutralising with ammonia, and adding acetate of lead; 
the boiling, as much as the addition of the acetic acid, contribut- 
ing to the elimination of the c. carminic acid, by decomposition. 
The p. carminic acid is soluble in acids, but the c. carminic acid 
is nearly if not quite insoluble in dilute acetic acid even at a boil- 
ing temperature. The addition of chalk to the cochineal may act 
partially by decomposing the alum, and the sulphate of lime so 
formed may prevent the fatty acids in the cochineal from being 
dissolved, and soiling the carmine ; but as for this purpose carbo- 
nate of magnesia would answer as well, and as it did not, and as 
lime was certainly contained in the carmine I examined, carmine 
I bought, as well as in my own, I infer that it is an essential 
ingredient of that colour. 
Hence we see too why owing to the extreme instability of 
¢. carminic acid, and to the fact that heat decomposes it, it is so 
necessary to avoid long-continued boiling in the preparation of 
a bright carmine, and why it is prudent to use so little alkali, 
and that saturated with carbonic acid in the operation. The 
excess of carbonate of lime by rendering the liquor neutral no 
doubt tends also to prevent the c. carminic acid from being pre- 
cipitated to the bottom among the dregs, and allows of the slow 
: 14—2 
