CONFLICTING OPINIONS AMONG CHEMISTS. 
retted iron, which has been considered a dedi- 
cate test, producing an orange-yellow precipi- 
tate or the hydro-sulphuret of arsenic. We 
prefer this to the experiment brought forward 
on this occasion, because 2 inc sometimes 
contains arsenic. Dilute sulphuric acid 
dissolves zinc : at the same time that the 
temperature of the solvent is increased, and 
much hydrogen escapes, an undissolved resi- 
due is left which, Proust says, is a mixture 
of arsenic, lead, and copper. 
But Dr. Christison has maintained that 
the liquid tests have been found liable to 
many fallacies, and their details have seldom 
carried conviction to the Judge or Jury ; it 
was therefore desirable in his opinion to 
obtain evidence from reduction and sublima- 
tion. He endeavoured to show that the fourSi 
part of a grain might be presented in its 
metallic form, although it had been dissolv- 
ed in eight thousand parts of the most com- 
plicated vegetable and animal fluids. The 
experiments that he performed led to the 
conclusion, that the proof of the existence 
of arsenic becomes conclusive ; for no other 
known substance, says he, can yield with 
sulphuretted hydrogen a yellow precipitate 
from which a metallic crust can be sub- 
limed. Professor Silliman says that ** the 
reduction of the arsenic is perfectly deci- 
sive.” After this we might well ask, what 
need is there of other tests ? 
But professor Michell has performed nu- 
merous experiments ; and, having closely 
examined those made by Christison, come to 
the conclusion that the more he examined the 
subject the more he became convinced that, 
” for the ascertainment of the presence of 
arsenic, no single experiment was sufficient," 
and that the appearances, of even the best 
marked and most characterestic ct'ust, arena t 
an infallible, or alone even a good test of the 
presence of the potent poison.” Rose de- 
clares that the free sulphur is always depo- 
sited along with the sulphurets precipitated 
from arsenical solutions by sul phuretted 
hydrogen, and which accounts for the yel- 
low or yellowish red ring occasionally sur- 
mounting the metallic crust obtained by the 
reduction of the sulphuret of arsenic. Dr. 
A. Murray of Edinburgh is not satisfied 
with Christison’s conclusions, and shows 
experiments by which, he says, it is easy to 
detect a quantity of arsenic, much less than i 
the most skilful chemist can reduce to the |i 
metallic state. Few persons, says he, can I 
depend upon reducing l-20th or even 1-lOth 
of a grain of arsenic ; but he felt con- 
vinced that it is easy, by his method, to de- 
tect 1-lOOOth part of a grain ; as a proof of 
which he took one grain of white arsenic, I 
and spread it out as much as possible upon f 
common writing paper ; and, by means of the 1 
ammoniacal nitrate of silver, with great ease !| 
and even in a hasty manner, made upwards r 
of 400 separate and distinct yellow spots. ^ 
Dr. Paris recommends the suspected fluid i 
to be dropped on a piece of white paper, 
making with it a broad line ; along this line 
a stick of lunar caustic is to be slowly I; 
drawn several times successively, when a 
streak is produced of a colour resembling I; 
that known by Indian yellow. Dr. Murray { 
denies that nitrate of silver produces change | 
of colour with arsenic ; but with a phosphate | 
it readily occasions a beautiful yellow. Orfila 
is in the habit of testing by concentrated i 
liquid hydro -sulphuric acid. He obtains the i 
metallic arsenic, and specifies its physical j 
properties. 
Now, considering the importance of the ’ 
question we have been examining, these con- | 
flictingopinions induce us to implore those who I 
are likely to sit on British juries and gentle- | 
men of the Bar, seriously to consider this ! 
difference of opinion ; while we solemnly j 
protest against any bold assurance of our | 
chemical physicians lest they peril the j 
life of a fellow creature on the uncertainty 
of an experiment. 
Many of our profession, says Dr. Wm. 
Hunter, are a little disposed to grasp at 
authority on a public examination, by giving 
a quick and decided opinion, whereit should 
have been guarded with a doubt, — acharacter 
which no man should be ambitious to ac- 
quire, v/ho in his profession is presumed 
every day to be deciding nire questions on 
which the life of a patient juay depend. 
