1884.] Microscopy and Histology. 325 
and others have given recipes) and from carmin (the impure com- 
mercial powder). The first mode of preparation, the one which 
I followed in preparing the acid upon which I have experimented 
is that of Warren De la Rue. Watts, whom I quote because he 
gives clear directions (Dict. Chem., 1863, vol. 1, p. 804), gives 
De la Rue’s method, as follows: “ To separate it [carminic acid] 
cochineal is exhausted with boiling water; the extract is pre- 
cipitated 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 evaporated to a syrupy 
consistence and dried over the water-bath ; and the dark purple 
product thus obtained is treated with alcohol 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 precipi- 
tating the aqueous extract of cochineal with neutral lead acetate 
slightly acidulated with acetic acid; decomposing the washed 
precipitate- with sulphuric acid; again precipitating the filtrate 
with Jead-acetate, and decomposing the precipitate with sulphuric 
acid, avoiding an excess; then precipitating a third time, and de- 
composing the precipitate with hydrogen sulphide. The filtered 
solution is evaporated to dryness; the residue dissolved in abso- 
lute alcohol ; the crystalline nodules of carminic acid obtained on 
ving this solution to evaporate are freed from a yellow sub- 
stance by washing with cold water, which dissolves only the car- 
minic acid ; and the residue left on evaporating the aqueous solu- 
tion is recrystallized from absolute alcohol or from ether.” 
Schaller’s mode of preparation gives purer carminic acid than 
Rue’s, but either kind is sufficiently pure for histological 
tp The precipitation by lead acetate and the dissolving in 
ohol free the carminic acid from animal impurities, and the 
Consequence is a purer form of pigment than can be extracted by 
red process hitherto employed for the preparation of carmin for . 
bee Bical purposes. I will here add that carminic acid has 
aren shown recently by Liebermann and Van Dorp to be related, 
rough nitrococcusic acid, to trinitrocresol, which has been ob- 
of ed from coal-tar cresol, thus showing that the coloring matter 
cochineal contains methylated benzine-residues. a, 
able. jaa prad aa pee carminic acid, ready gp oe 
ie emical student could easily prepare it the pro- 
PS Siven above. y Aiha $ i 
aii unnecessary to explain to naturalists the advantages of 
ree ig Solutions of ipinta over aqueous ones. The alcoholic 
tion oer Preparations much quicker than the aqueous solu- 
> pa? for coloring sections I employ a solution of 0.25 gram 
acid to-100 grams of eighty per cent: alcohol, and leave 
