158 On Tests for the Discovery of Arsenic. 
I used in these experiments, a chromat of potash made in 
the imperfect and impure way in which Dr. Porter used it; 
and also another solution made in the usual way. That 
is, I took two oz. avoird of triturated chromated iron, and 
added to it, one oz. avoirdupois of triturated nitre : to other 
two oz. avoirdupois of chromated iron, I added one oz. of 
dried salt of tartar: I exposed them in separate crucibles to 
a full red heat for 11 hour (side by side) ina common forge : 
I washed the contents of each crucible in the same quantity 
of boiling water, and filtered. On testing them with super- 
acetat of lead, the yellow produced by the nitrated chroma- 
ted iron, was of a richer colour than the other ; which last 
contained not only uncombined alkali, but also a portion of 
oxyd of iron, which covered the precipitate of lead. But 
in making the experiments detailed in this paper, I found 
no perceptible difference of result between the two solu- 
tions. In this variance between Dr. Porter’s experiments 
and mine, it is desirable that other persons should repeat 
them ; and with this view I transmit to you these remarks. 
The subject ought to be investigated in every point of view, 
until our chemists are enabled tosay before a court and a ju- 
ry, ‘“‘ we do possess sure and accurate means of detecting 
the poison of arsenic.” 
Of the methods hitherto proposed for this purpose, the fol- 
lowing appears to me the best ; deduced from the result of 
my own experiments, and of the chemists who have prece- 
ded me. 
Suppose a man suspected of being poisoned by arsenic : 
let the ejections from his stomach, (and the contents of his 
stomach, if dead,) be examined carefully with a magnifying 
glass, to discover the particles of white arsenic in substance, 
which should be’set aside for experiment. If you find no 
such appearance, let the matter ejected, and contained, be 
fully dried in a heat of not less than 100° Fah. Take some 
of the dried matter, triturate it with ;';th ofits weight of dry 
lamp black, ivory black, orcharcoal ; intoa glass tube six or 
nine inches long, half aninch wide, and closed atone end, put 
as much of this mixture as will fill the tube from half an inch 
to an inch deep; stop the open end lightly with a cork ; ex- 
pose the matter in the flame of an oil or spirit lamp, and if 
there be any arsenic, it will shortly sublime in black shining 
metallic particles toward the upper end of the tube. ‘These 
