RESEARCH FOR ARSENIC AND ANTIMONY. 
35 
arsenic can be detected in the minimum quantity of liquid 
required for the use in Marsh’s tube. From experiment I 
find, that deposits may be obtained from the 2000th part of 
a grain, and that they assume a reliable character, and admit 
of the application of corroborative tests, when the weight of 
arsenic reaches the 1-100th of a grain. By a mode of opera¬ 
ting different from that advised by Mr. Marsh, it is possible 
to extract and procure, in a visible metallic deposit, the whole 
of the metallic arsenic contained in the 2000th and even in 
the 4000th part of a grain of arsenious acid; but to these 
small quantities it is difficult, if not impossible, to apply the 
requisite number of corroborative tests. 
Mr. Marsh intended that his method of detecting arsenic 
should be substituted for the ordinary process of reduction 
and the use of the liquid and gaseous tests ; but its claims to 
consideration rested upon an entirely different ground, 
namely, the power which it conferred on chemists, for the 
first time, of detecting the poison in the soft organs and 
fluids of the body. Up to the date of this discovery there 
were no chemical proofs that arsenic was absorbed or depo¬ 
sited in the tissues of the living body. In reference to the 
application of the process to organic substances, Mr. Marsh 
advised that, if the suspected substance was a solid, it should 
be boiled with two or three ounces of water, and the liquid 
filtered and introduced into the tube. If it was liquid, such 
as thick soup, the contents of the stomach, gruel, tea, cocoa, 
&c., he simply recommended that it should be thrown on a 
filter to separate the more solid parts, and that the liquid 
portion should be placed in the tube or inverted bottle in 
which the hydrogen was generated. Thus, then, he brought 
every substance to the liquid state, while he made no attempt 
to separate the organic matter; or, when the poison was in 
small quantity, to reduce the bulk of the liquid by previous 
concentration. On the contrary, his plan simply consisted 
in enlarging his apparatus for large quantities of liquids. In 
one experiment, he operated on half a gallon of water con¬ 
taining one grain of arsenic; and in another he states that 
he obtained equally satisfactory results from operating at 
once on three pints of very thick soup, the same quantity of 
port wine, porter, gruel, tea, &c. In these analyses of large 
quantities of liquids, the process of evolving the gas was 
allowed to proceed very slowly, and several days elapsed 
before the mixture ceased to give indications of the presence 
of arsenic. In order to prevent the effect of the frothing 
arising from the generation of hydrogen in an organic liquid, 
Mr. Marsh recommended the greasing or oiling of the shorter 
