PRESENCE OF ARSENIC. 615 
if the counsel employed for his defence be not 
assisted by the evidence, or instruction, of some 
one skilled in the principles and practice of che- 
mistry. 
BottTon-LE-Moors, 
Jan. 25th, 1841. 
APPENDIX TO THE FOREGOING 
PAPER. 
In the London and Edinburgh Philosophical 
Magazine, published yesterday, I find a com- 
munication from Mr. Marsh, “ On testing for 
Arsenic and Antimony, by Hume's Process,” in 
which he sabmits to the readers of that journal, a 
modification of the mode of applying Hume’s test 
(the ammoniacal nitrate of silver) which he 
described in the said journal, published October, 
1839. Instead of the drop of water, suspended 
to the inverted glass, being held over the flame 
of gas, and the ammoniacal nitrate of silver being 
afterwards applied, he, at once, having moistened 
one side of a piece of glass with the test solution, 
holds it, with the moistened side downwards, over 
the flame, when, if arsenic be present, the charac- 
teristic yellow precipitate is produced, and, if 
