RESEARCH FOR ARSENIC AND ANTIMONY. 
39 
Arsenic and antimony are thus very easily identified when 
Marshes original process of burning the gas is resorted to. 
Many other distinctions have been suggested ; ‘but it is not 
necessary to specify these, as the above characters serve to 
distinguish the two metals clearly from each other, and both 
of them from all other metals known to chemists. The 
original process of Marsh is by no means so well adapted for 
the detection of antimony as of arsenic. The antimony 
when introduced into the tube in a state of acid solution, if 
in small quantities, is liable to be rapidly precipitated on the 
zinc in the form of a black powder, and the current of gas 
soon ceases. When the 1-100th of a grain of tartar emetic 
was dissolved and placed in the • tube with pure water and 
hydrochloric acid, there was not the slightest indication of 
the presence of antimony. It was only when the quantity 
amounted to about a grain, that a number of well-marked 
deposits, in a state fitted for testing, could be procured by 
the combustion of the gas. In employing this process, we 
may meet with deposits so small and ambiguous from their 
thinness, that the corroborative tests may fail to show their 
nature. In this case, it will be advisable not to rely upon 
the combustion of the gas, but upon its decomposition by 
heat, and the reagents to be hereafter described. 
As a result of this examination of the process of Marsh, 
it may be stated that there are two difficulties which the 
analyst encounters in resorting to it for the separation of 
arsenic from the solids or fluids of the body. First, there is 
no good or simple method of bringing the arsenic to a con¬ 
centrated state, i.e., to a state fitted for testing, without pro¬ 
ducing froth; and secondly, when the quantity of arsenic in 
an organic liquid is so small as to render the adoption of the 
process necessary, it is not possible to follow the plan of the 
inventor, of generating the hydrogen in the whole quantity 
of the organic liquid. 
The chemical facts upon which this process is based had 
been Ions: known to scientific men, but it is not the less 
creditable to Mr. Marsh that he should have been the first 
to make a practical application of them for the detection of 
arsenic. Arseniuretted hydrogen was discovered by the 
Swedish chemist, Scheele, about the year 1775. He proved 
that it was a combustible gas, and that one of the results of 
its combustion was a regulus of (metallic) arsenic. Proust, 
in 1806, Trommsdorf, in 1803, and Stromeyer, in 1806, suc¬ 
cessively examined the gas, and described methods for its 
production. Stromeyer found that it burnt with a blueish 
white flame, and that the products of its combustion were a 
