GENERAL NOTES. 129 
in the leading chemical dictionaries and hand-books to be readily 
soluble in water and in alcohol. Watts (Dict. Chem., 1872, Ist 
suppl., p. 413) says of carminic acid: “ This acid forms a purple 
mass, fusible and soluble in all proportions in water and in alco- 
hol. Sulphuric acid and hydrochloric acid dissolve it without 
alteration. It bears a heat of 136° C. without decomposition.” 
Pepier still, Watts (Dict. Chem: 1863, V. I, p. 804) says: 
“The fine red pigment known in commerce as carmin is pre- 
pared by treating a solution of cochineal with cream of tartar, 
alum, or acid oxalate of potassium. The fatty and albuminous 
matters then coagulate and carry down the colouring matter 
with them.” Now, in preparing most carmin solutions this pre- 
cipitation takes place, and the carmin, having greater cohesive 
(not chemical) affinity for impurities of animal origin than for 
alcohol, its solution is not readily accomplished by that medium, 
nor indeed by water. In preparing carmin solutions for histo- 
logical purposes by some of the published recipes, more than 
one-half of the coloring matter of the carmin is lost in the refuse 
left upon the filter-paper. 
There are two ways commonly in use for preparing carminic 
acid, which term I here use as distinguished from “ acid carmin ” 
(the cochineal decoction for which Grenacher, Schweigger-Seidel, 
and others have given recipes) and from carmin (the impure 
commercial powder). The first mode of preparation, the one 
which I followed in preparing the acid upon which I have ex- 
perimented is that of Warren de da Rue. Watts, whom I quote 
because he gives clear directions (Dict, Chem., 1863, Vol. I, p. 
804), gives De la Rue’s method as follows :—“ To separate it 
[carminic acid] cochineal is exhausted with boiling water ; the 
extract is precipitated by subacetate of lead slightly acidulated, 
care being taken not to add the lead-solution in excess; the 
precipitate is washed with distilled water till the wash-water no 
longer gives a precipitate with a solution of mercuric chloride, 
then decomposed by sulphuretted hydrogen ; the filtrate is eva- 
porated to a syrupy consistence, and dried over the water-bath ; 
and the dark purple product thus obtained is treated with alco- 
hol, which extracts the carminic acid.” The second mode of 
preparing carminic acid, that of Schaller, is given by Watts 
(Dict. Chem:, 1872, 1st suppl., p. 413) as follows: “C. Schaller 
prepares this acid by precipitating the aqueous extract of cochi- 
neal with neutral lead acetate slightly acidulated with acetic acid ; 
decomposing the washed precipitate with sulphuric acid ; again 
precipitating the filtrate with lead-acetate, and decomposing the 
precipitate with sulphuric acid, avoiding an excess; then preci- 
pitating a third time, and decomposing the precipitate with hy- 
drogen sulphide. The filtered solution is evaporated to dryness ; 
the residue dissolved in absolute alcohol ; the crystalline nodules 
of carminic acid obtained on leaving this solution to evaporate 
are freed from a yellow substance by washing with cold water, 
which dissolves only the carminic acid; and the residue left on 
evaporating the aqueous solution is recrystallized from absolute 
alcohol or from ether,” 
