On Tests for the Discovery of Arsenic. 159 
when collected, will exhibit the white stain when heated 
with copper, and the garlic odour when thrown upon hot 
coals, which are peculiar to arsenic. If this appearance 
takes place in the tube, you need proceed no further, unless 
to make security doubly sure. 
Take another sufficiently large portion of the dried mat- 
ter: boil it in rain or distilled water for one fourth of an 
hour in a florence flask, or other convenient vessel. Filter; 
concentrate the filtered solution, and keep it for experiment. 
Take of this filtered solution three portions, in three sepa- 
rate wine glasses, or clear watch glasses: drop into one 
portion a few drops of carbonat of potash to saturate the arse- 
nious acid 5 then add a drop or two of sulphat of copper ; 
if a green precipitate appears, it affords strong prima facie 
evidence of the presence of arsenic. 
Take another portion of the filtered solution ; drop into 
it a few drops of chromat of potash ; wait half an hour; 
if a bright grass-green colour is produced, it forms another 
evidence that arsenic is present. To this green solution, 
add a drop of ammonia, if no blue colour be produced, you 
may rest assured that the green colour is produced not by 
copper but by arsenic. I trust with confidence to this test, 
which detects the twentieth part of agrain of arsenic, wheth- 
er in powder or solution. 
Take the third portion ; try it with nitrated silver and 
ammonia, in the manner directed by Dr. Marcet. Ifadense 
yellow precipitate appears, there is surely arsenic. The fil- 
tered solution may be tried in the first instance for copper, 
by a drop of ammonia, which will disentangle you at once 
from Dr. Porter’s ambiguities ; for a glass rod dipt in am- 
monia, like the touch of Ithuriel’s spear, will make the cop- 
per start up at once in its true colour. 
Nor indeed is it likely that the crime of poisoning will ev- 
er be attempted with copper, whose decidedly nauseous 
taste and emetic property, renders it a very inapt instrument 
of crime. When it is taken accidentally, ammonia will al- 
ways discover it, if in a quantity to do harm. As to the 
preparations of chrome, they are so very unlikely to occa- 
sion mischief either by accident or design, that they may be 
considered as quite out of the question; and Dr. Porter’s 
cautions as superfluous in this point of view. 
