74 
SELECTED ARTICLES. 
a moment. On this account, this mode of trial has been 
abandoned. That of M. Anthon is based upon the property 
which hydrate of alumina possesses of precipitating carmine 
completely from its solution, so that the liquid shall become 
clear and colorless. There are only necessary for this method 
a graduated cylinder and some proof liquid. 
The cylinder consists of a tube of glass, from three-fourths 
to an inch in diameter, and from twenty to twenty-four 
inches in length; it is sustained upon a glass bottom, which 
renders it more convenient for use. Into this tube is poured 
an aqueous solution, made with seven grains of pure dry 
carmine; it is prepared by exhausting powdered cochineal 
with water, evaporating the liquid by gentle heat to the con- 
sistence of an extract, treating the product by boiling alcohol, 
filtering, and evaporating to dryness; the coloring matter left 
is called carmine. For the purpose of experimenting, seven 
grains of it are taken, and dissolved in the necessary quantity 
of water, to occupy in all but three inches of the tube. From 
the point reached by the liquid, the graduation of the tube com- 
mences and proceeds upwards; this point is the zero of the 
scale. The proof liquid is then poured in little by little, and 
the vessel is shaken so as to agitate the liquid at each addition, 
and the lake colored carmine which forms is then allowed to 
deposit. This is continued until the liquid becomes colorless. 
At this point, the number seventy is marked, and the space 
included between and 70 is divided into seventy equal parts, 
each one of which corresponds to the quantity, per centum, 
contained in the cochineal. The author has been induced 
not to make this instrument longer, and not to divide it into 
a greater number of degrees, because, according to him, there 
is no cochineal which contains more than seventy per cent, 
of pure coloring matter. 
To obtain the proof liquor, one part of alum is dissolved in 
thirty-two of water, and ammonia is added, until it ceases to 
throw down a precipitate, taking care not to add an excess of 
ammonia. It is this white homogeneous mixture, having a little 
gelatinous consistence, that constitutes the proof liquor. We 
