130 JOURNAL OF SCIENCE. 
Schaller’s mode of preparation gives purer carminic acid 
than De la Rue’s, but either kind is sufficiently pure for histo- 
logical purposes. The precipitation by lead acetate and the dis- 
solving in alcohol free the carminic acid from animal impurities, 
and the consequence is a purer form of pigment than can be ex- 
tracted by any process hitherto employed for the preparation of 
carmin for histolegical purposes. 
I will here add that carminic acid has been shown recently 
by Liebermann and Van Dorp to be related through nitrococcusic 
acid to trinitrocresol, which has been obtained from coal-tar 
cresol ; thus showing that the coloring matter of cochineal con- 
tains methylated benzine residues. I do not know whether 
carminic acid, ready prepared, is obtainable. Any chemical 
student could easily prepare it by the processes given above. 
It is unnecessary to explain to naturalists the advantages of 
alcoholic solutions of carmin over aqueous ones. The alcoholic 
solution colors preparations much quicker than the aqueous so- 
lution does ; for coloring sections I employ a solution of 0.25 
eram carminic acid to 100 grams of 80 per cent alcohol, and 
leave sections in the solution from two to five minutes. A solu- 
tion of equal carmin strength but in absolute alcohol, can be 
employed ; it has, however, no special advantages, since with 
the 80 per cent. alcoholic solution the sections can be washed 
directly in absolute alcohol, and then put into oil of cloves or 
turpentin. Coloring in the piece before sectioning never takes 
as long with alcoholic carminic acid as it does with ordinary car- 
min solutions, and if it did take long the strong alcohol would 
preserve the tissue from maceration. In coloring pieces of mol- 
lusca, or of other equally slimy animals, the slime should be 
removed beforehand or the coloration will be unsatisfactory, 
because the slime congealing in the alcohol takes up the coloring 
matter, forming an almost impervious colored layer on the out- 
side and leaving the inside of the piece nearly uncolored. 
Some preparations colored in alcoholic carminic acid and 
then put up in glycerin, lost their color in a few months, the 
color seeming to be entirely diffused in the glycerin, while similar 
preparations mounted in Canada balsam retained their color 
perfectly. I do not know if this fading would occur with pre- 
parations colored with alcoholic ammonic carminate, or even if 
this diffusion was not due to some impurity of the glycerin (of 
the purity of which I was doubtful) ; time to test this matter 
further failed. 
An alcoholic ammonic carminate, or ammonia carmin, can 
be prepared at a moment’s notice, from alcoholic carminic acid, 
by dropping ammonia drop by drop, and stirring until the entire 
solution changes from its bright red to a purple red. By this 
mode pure alcoholic ammonic carminate can be produced with 
no excess of ammonia, and at any time. As the carminic acid 
can be preserved dry without decomposition, and dissolves 
quickly in alcohol, one can carry the ingredients of a carmin 
solution in the vest pocket without inconvenience, 
