172 
MEDICO-LEGAL CONTRIBUTIONS ON ARSENIC. 
the whole with a glass rod. After allowing it to settle, pour 
off' the water, without disturbing the sediment. To this 
water should again be added, and the operation repeated. 
In the bottom of the vessel may often be seen arsenious acid 
in the form of small, white particles, which feel gritty and 
grate under the glass rod. These are to be taken out and 
dried. As simple tests, one or more may be gently heated in a 
glass tube sealed at one end, and another in a similar tube 
with carbonate of soda. If in the first tube is produced a 
white, crystalline deposit, and in the second a black, metallic 
mirror, it is pretty decisive evidence of the existence of 
arsenic. 
Stomach, Intestines, ^c, —If the intestinal track is to be 
examined, it should be completely opened, and its appearance 
carefully observed. 
Very often particles of arsenious acid may be seen adhering 
to the mucous membrane, which may be tested in the manner 
just mentioned. 
3. Division of Materials for Analysis. —Mechanical division 
facilitates chemical action ; it is, therefore, proper to minutely 
divide organic substances before commencing their analysis. 
This may be done by a pair of scissors or small shears; but 
where a considerable quantity of animal matter is to be 
operated upon, a small new meat chopper (consisting of 
an iron cylinder containing a set of revolving knives) may 
most conveniently be employed. such an apparatus, in 
five or ten minutes, the various parts, as the stomach, in¬ 
testines, liver, kidney, &c., may be converted into an almost 
homogeneous pulpy mass, and thus be in the best condition 
for being acted upon by chemical agents. 
4. Necessity of a Preliminary Examination. —From what has 
already been said of the fallacies of chemical evidence, and 
the nature of the errors that may arise, it is evident that in 
cases of suspected poisoning the chemical examination ought 
only to be entrusted to experienced and reliable men. No 
amount of labour ought to be spared in such an examination 
in obtaining reliable results, for an error may cost a human 
life, and from the fact of impurities of a poisonous character 
occurring in our chemicals, &.C., there exists, in my opinion, 
a real necessity for a thorough preliminary examination. 
Portions of animal or vegetable matter, as the case may be, 
equal in weight to the articles afterwards to be examined, 
ought to be taken and subjected, in the same vessels and 
apparatus, to the same processes, by the use of portions of 
the same reagents in as large a quantity as will afterwards 
be used in the actual examination. 
