§ 36 .] PROCEDURE IN SEARCHING FOR POISON. 51 
work on Foods , the figure of which is here repeated (see the 
accompanying figure). With a good water-pump having a sufficient 
length of fall-tube, a vacuum may be also obtained that for practical 
purposes is as efficient as one caused by mercury ; if the fall-tube 
delivers outside the laboratory over a drain, no offensive odour is 
experienced when dealing with putrid, stinking liquids. A vacuum 
having been obtained, and the receiving flask surrounded with ice, a 
distillate for preliminary testing may be generally got without the 
action of any external heat ; but if this is too slow, the flask containing 
the substances or liquid under examination may be gently heated by a 
water-bath : water, volatile oils, a variety of volatile substances, such as 
prussic acid, hydrochloric acid, phosphorus, etc., if present, will distil 
over. It will be well to free in this way the substance, as much as 
possible, from volatile matters and water. When 
no more will come over, the distillate may be care¬ 
fully examined by redistillation and the various 
appropriate tests. 
The next step is to dry the sample thoroughly. 
This is best effected also in a vacuum by the use of 
the same apparatus, only this time the receiving- 
flask is to be half filled with strong sulphuric acid. 
By now applying very gentle heat to the first flask, 
and cooling the sulphuric acid receiver, even such 
substances as the liver in twenty-four hours may 
be obtained dry enough to powder. 
Having by these means obtained a nearly dry 
friable mass, it is reduced to a coarse powder, and 
extracted with petroleum ether, and treated as 
under the special section for Alkaloids and Glucosides (see Index). 
It must also be remembered that there are a few metallic compounds 
(as, for example, corrosive sublimate) which are soluble in alcohol and 
ethereal solvents, and must not be overlooked. 
The residue, after being thus acted upon successively by petroleum, 
by alcohol, and by ether, is both water-free and fat-free, and also devoid 
of all organic poisonous bases and principles, and it only remains to 
treat it for metals, various processes for which are as follows. These 
processes have been devised chiefly for the detection of arsenic and 
antimony, but evidently may be used, with obvious limitations, for most 
mineral matters. 
A very fair and complete analysis may be made from a small amount 
of material. The process is, however, somewhat faulty in reference to 
phosphorus, and also to oxalic acid and the oxalates ; these poisons, if 
suspected, should be specially searched for in the manner to be more 
particularly described in the sections treating of them. I 11 most cases 
a 
This figure is from 
Foods. B is a 
bell-jar, which can 
be adapted by a cork 
to a condenser; Ris 
made of iron; the 
rim of the bell-jar is 
immersed in mer¬ 
cury, which the deep 
groove receives. 
