MEDICO-LEGAL CONTRIBUTIONS ON ARSENIC. 
437 
the matter to be examined, it is desirable to concentrate it in 
a water bath, or at a temperature not exceeding 212° F.; it is 
then to be treated as indicated below. 
Solid matter, such as the liver, stomach, &c., after being 
finely divided, is to be placed in a porcelain evaporating-dish, 
and mixed with chlorhydric acid and water until it forms a 
thin paste. Jt is neither desirable nor necessary to use a 
very strong acid; an acid having the density of 1*11 is suffi¬ 
cient. The dish is then to be placed upon a water bath, or 
over a lamp, and gently heated at a temperature not exceed¬ 
ing 180° F. Chlorate of potash is then to be added, in 
portions of from ten to twenty grains, every five minutes or 
thereabouts, occasionally stirring the mixture until the whole 
is converted into a light yellow homogeneous liquid, when it 
is allowed to cool. (The fatty matters are with difficulty 
destroyed, nor is their decomposition generally absolutely 
necessary ; they solidify upon cooling, and are easily re¬ 
moved.) The liquid is now to be placed upon the sand bath, 
and heated until the smell of chlorine has disappeared. By 
the action of the chlorhydric acid upon the chlorate of potash, 
chlorine compounds are evolved, which decompose the 
organic matter, and convert any arsenic that may be present 
into arsenic acid. After cooling, the liquid is to be filtered, 
and the filtrate carefully preserved ; the residue remaining 
upon the filter is to be thoroughly washed, and the washings 
collected in a separate vessel; if in large quantity they may 
be evaporated to the bulk of three or four ounces, and are 
then to be added to the original liquid. (The residue may 
contain sulphate of lead.) 
2. Treatment hj sulpliydric acid (H S).—The mixed fluid is 
poured into a beaker glass, and a slow stream of washed 
sulphydric acid passed through it for twelve hours; it is then 
to be allowed to remain at rest for the same length of time. 
This treatment precipitates any arsenic, mercury, antimony, 
copper, &.C., that may be present in the form of the corre¬ 
sponding sulphide, together with a portion of organic matter. 
The liquid is afterwards filtered, and the precipitate washed 
until a small portion of the washings gives no precipitate 
with nitrate of silver, thus indicating the absence of chlorine. 
(Tlie filtrate and washings may contain zinc, &.c.) 
The production of a precipitate by sulphydric acid does not 
of itself indicate that any metals were in solution, since 
organic matter, even if alone, is precipitated under these 
circumstances. 
3. Purification of the precipitate .—It is to be particularly 
noted that in order to obtain satisfactory results, all the 
XXXVI. ‘ 29 
