Orobanche Virginiana. 38 
in the management of many cases of this dreadful disease, has been 
acknowledged by the regular practitioners of Philadelphia, &c. 
several persons whom I called into the room where I made the experiment, and who 
knew nothing of the object of my enquiries. After this with some difficulty I picked 
out about three or four grains of the white powder, and bound them between two pieces: 
of copper, which I threw into the fire. After the copper pieces became red hot, I took 
them out of the fire, and when they had cooled, discovered an evident whiteness im- 
parted to both of them. One of the pieces afterwards looked like dull silver. These 
two tests have generally been thought sufficient to distinguish the presence of arsenic 
in any bodies ; but I made use of a third, which has lately been communicated to the 
world by Mr. Bergman, and which is supposed to be in all cases infallible. 
s¢T infused a small quantity of the powder in a solution of a vegetable alkali in water 
for a few hours, and then poured it upon a solution of blue vitriol in water. The colour 
of the vitriol was immediately changed to a beautiful green, and afterwards pre- 
cipitated. 
aoe | shall close this paper with a few remarks upon this powder, and upon the cure of 
cancers and foul ulcers of all kinds. 
«1, The use of caustics in cancers and foul ulcers is very ancient, and universal. But 
I believe arsenic to be the most efficacious of any that has ever been used. It is the 
basis of Plunkett’s, and probably of Guy’s well known cancer-powders. ‘Phe great art 
of applying it successfully, is to dilute and mix it in such a manner as to mitigate 
the violence of its action. Dr. Martin’s composition was happily calculated for this 
purpose. It gave less pain than the common or lunar caustic. It excited a moderate 
inflammation, which separated the morbid from the sound parts, and promoted a plen- 
tiful afflux of humours to the sore during its application. Tt seldom produced an escar 3 
hence it insinuated itself into the deepest recesses of the cancers, and frequently sepa- 
VOL. Il. 5 
