48 THE VOLATILITY AND SOLUBILITY OF CANTH ARIDIN. 
acetic acid , phosphoric acid 3 and the phosphate of lime and magnesia. 
It is proverbial among apothecaries and physicians, that the 
pharmaceutical preparations designed to produce vesication, 
vary very much in their power as prepared by different indi- 
viduals, and from different samples of cantharides by the 
same recipes. Is this variableness of power due to the 
inequality of strength of the commercial drug? or are we to 
attribute it to the treatment employed by the Apothecary? 
The real importance of these queries demands an answer. 
To proceed properly, the investigator should examine can- 
tharidin in a pure state, ascertain how far the statements of 
writers are correct, then by a series of analyses, quantitative 
as regards that principle, determine whether its proportion 
varies, and to what extent, in different specimens of can- 
tharides of fair quality; and finally test the preparations 
derived from the same samples and see how far they corres- 
pond with the inferences drawn from the ascertained 
properties and proportions of the active principle. I have 
at present undertaken to resolve but a part of these queries 
— yet by far the most important ones — as will be seen. 
“ Cantharidin is a white, neutral substance, of which the 
formula, according to Regnault, is C ]0 H 0 4 . Gmelin con- 
siders it of the nature of a solid volatile oil. As usually seen, 
it has the form of minute flattened four-sided prisms much 
broken up, so as to appear like scales- When deposited 
from an ethereal solution of cantharides by slow evaporation, 
or from its solution in hot acetic acid by cooling, it assumes 
the form of flattened oblique four-sided prisms with dihedral 
summits, derived from the rectangular prism by the bevel- 
ment of its edges. The crystals by slow sublimation are 
four-sided rectangular prisms of great brilliance and some- 
times iridescent. 
“ Solubility. — Pure cantharidin is insoluble in water hot or 
cold. It is slightly soluble in cold alcohol, readily so when 
hot. Ether dissolves it to a greater extent, yet much more 
easily hot than cold. Chloroform is its best solvent, cold or 
hot, as shown in a former essay (Am. Jour. Pharm. 3 vol. xxiii, 
124,) and will remove it from the aqueous infusion of the 
flies. Acetic ether dissolves cantharidin, especially when hot, 
but does not retain much on cooling. 
te Volatility. — At 220° F. no visible effect was produced. 
Kept at 250° F. for twenty minutes, a very slow sublimation 
commenced. At 300° F. the vaporisation was but slightly 
increased. The heat was then raised to 360° F., when the 
sublimation became more decided, yet still slow. Between 
