84 
ON CANTHARIS VESICATORIA. 
fixed oils. The active principle itself may indeed be entirely 
extracted, without even injuring the color. 
Cantharides should not as a general rule be purchased in 
powder, except when entire confidence is placed in the ven- 
der ; and then it is important to ascertain that they have been 
recently reduced to that state. 
Analysis. 
Various attempts to analyze cantharides were made by 
many chemists, but no very satisfactory results were ob- 
tained, until the subject was taken up by Robiquet in 1810. 
After an elaborate analysis, he found them to contain the 
following constituents, viz. 1. A green oil, insoluble in 
water, but soluble in alcohol and inert as a vesicatory. 2. 
A black matter soluble in water, insoluble in alcohol, and 
inert. 3. A yellow viscid matter soluble in alcohol and 
water, likewise inert. 4. Cantharidin. 5. A fatty matter 
insoluble in alcohol. 6. Phosphates of lime and magnesia, 
acetic acid, and, in the recent state, a small quantity of uric 
acid. 
Orflla has since discovered a volatile principle, upon 
which the peculiar disagreeable odor of the fly depends. It 
is separable by distillation with water. 
Cantharidin, the substance on which the blistering pro- 
perty depends, is prepared by boiling cantharides in water 
until every thing soluble in that liquid is taken up ; then 
evaporate to the consistence of a thick syrup, and boil it 
continually in alcohol until that liquid ceases to act upon it ; 
evaporate the solution thus obtained to dryness over a 
water bath, and put the residue in a well-stoppered bottle 
containing ether, and shake the mixture for a considerable 
time. The ether at first will seem not to be effected by it, 
but after a few hours it will assume a beautiful yellow 
color. Then separate the solution from the precipitate by 
decantation, and allow it to evaporate spontaneously in a 
dry atmosphere. After evaporation, the result will be found 
