412 
MEDICO-LEGiVL CONTRIBUTIONS ON ARSENIC. 
of rubber tubing. A convenient sized tube is one of about 
three sixteenths of an inch external diameter, and about two 
thirds of this diameter within. It is advisable to draw out 
the tube at points from two to two and a half inches asunder, 
and also at the end of a jet; for a small deposit produced in 
a constriction may be more distinctly seen than if in another 
part of the tube. A number of these tubes, thoroughly 
cleansed, and from twelve to eighteen inches in length, 
ought to be previously prepared. The tube may be heated 
by an ordinary alcohol lamp, more conveniently by a Bunsen^s 
gas-burner, enclosed by a sheet-iron case (supported by a 
jjerforated cork moving on the stem of the burner), thus pre¬ 
venting the flame flickering by currents of air. 
It is not necessary to give in detail the proper mode of 
using the apparatus ; suffice it to say that zinc and water 
being placed within the generator, diluted sulphuric acid 
(one of acid to three of water), previously cooled, is to be 
added. When the air is driven out the tube may be heated; 
if, after the lapse of an hour or two, no stain is produced in 
the tube, the supposed arsenical liquid may be introduced 
and tested. It is advisable to obtain mirrors at different 
parts of a number, of tubes, and spots upon a number of 
pieces of porcelain, such as crucible covers; if the arsenic 
is present in but minute quantity, no spots can be obtained 
on the porcelain. (See FlandiiTs method of procedure, 
‘ Traite de Poisons,’ t. i, p. 621.) The delicacy of Marsh’s 
test is very great; thus Storter shows that the ^^ ^th of a 
grain of arsenious acid in more than ten million times its 
weight of water will give a distinct stain in the reduction 
tube. Acad. Arts and Sciences^ Proc. vol. viii, p. 79.) 
We may notice briefly some of the more simple modes of 
distinguishing between the mirrors and spots produced by 
arsenic and antimony. 
1. Treatment of the mirrors in the reduction tube. — a. The 
arsenical mirrors are always produced beyond the heated 
part, while antimoniuretted hydrogen, being more easily de¬ 
composed by heat than is arseniuretted hydrogen, produces 
a mirror before as well as beyond the heated part. 
h. Arsenic mirrors are of a lustrous, blackish-brown 
colour, and when thin are semi-transparent. Antimony 
mirrors are fused into small, silver-white globules, near the 
heated part of the tube; beyond, they are dull and almost 
black. 
c. If a very slow stream of dry sulphydric acid is passed 
into the tube, and the mirror is gently heated, it will, if 
