7 
Means of detecting Arsenic in the Animal Body, §c. 283 
% ordinary zinc of the necessary purity to be used in Marsh’s 
apparatus. : 
_ Sulphuric acid may contain arsenic, whe manufactured with 
sulphur obtained ‘from pyrites holding that ibetsinen in combina- 
tion; but a simple distillation will serve to rid it of this impurity. 
After placing *thé*zific, sulphuric acid and water in the appa- 
tus, replace the cork with the glass tube inserted in it, and 
when the hydrogen has been allowed to generate a sufficient 
length of time to expel the air, inflame it as it issues from the 
extremity of the tube; if a porcelain plate be. now applied to 
about the middle of the flame, and no tache or spot be obtained, 
we have the best evidence of the purity of our materials. 
“Another apparent objection to the apparatus, is, that the intro- 
duction of animal matter, either solid or liquid, causes the for- 
mation of a large quantity of froth, which arrests. the progress 
of the operation. This, however, is so easily remedied, that it 
need hardly be considered an objection. If the froth be not 
in too great quantity, it will suffice to introduce a little oil, 
Which will serve to arrest its formation. Another method is to 
turn the liquid out of the phial into a funnel, with the finger 
placed upon the lower extremity, the froth will at once rise to 
the surface, and by taking away the finger the liquid will pass 
out perfectly free from it. Again, if care be taken to ‘carbonize 
the matter before using it, this obstacle will be removed. There 
is still another means, and I find it to succeed very well in most 
instances ; it is to pour the sulphuric acid destined for the for- 
Mation of the hydrogen first upon the animal matter, and then 
Pour the two upon the zinc and water; it would appear that a 
Partial carbonization takes place. No doubt most persons will 
how perceive that this objection possesses no weight, and vanishes 
altogether before the means proposed to encounter it. 
The next part of this question to be examined, is, what sub- 
stances besides arsenic produce taches with this apparatus, and is 
there no danger of confounding them with that of arsenic? 
They are antimony, sulphur, phosphorus and iron. — Before 
Speaking of their distinguishing characteristics, it would be as 
Well to say a few words concerning that produced from arsenic. 
The arsenical tache is highly metallic, of a steel color, with a 
slight reddish tinge, and borders of a dark rusty color; but to 
¥e a proper idea of its appearance, as well as that of the others, 
& 
