ON THE DETECTION OF ARSENIC. 
291 
prevent the frothy effervescence choking the tube, the same 
results may be obtained as with the other apparatus. 
Marsh directs that the matter to be submitted to examination, 
if not in the fluid state, such as pastry, pudding, or bread, be 
boiled with two or three ounces of pure water for a sufficient 
length of time, and then thrown upon a filter to separate the 
more solid parts. Thick soup and the contents of the sto- 
mach to be also diluted with water and filtered, but tea, coffee, 
cocoa, &c, water, gruel, wine, spirits or malt liquors, can be 
operated upon without any previous process. 
A modification of Marsh's apparatus has been proposed by 
Orfila, consisting of an ordinary vial, closed by a cork pierced 
with two holes, which give passage, the one to a straight tube 
of a foot long which plunges into the liquid, the other to a 
tube bent at right angles, with one extremity a short distance 
below the cork, while the other is drawn out to a fine point 
whence the gas issues. (See fig. 6th.) 
To avoid the frothy effervescence which pushes a portion 
of the liquid out of the apparatus, and prevents the hydrogen 
gas from burning, and to dispense with the use of oil, which 
has been indicated in this circumstance Mr. Orfila, has enter- 
tained the happy idea of destroying the organic matter by 
burning it with nitrate of potash, and thus rendering the ex- 
traction of the arsenic more easy. 
His new disposition of the apparatus permits the introduc- 
tion of the suspected liquid into the vial without uncorking it. 
i The test with hydrogen is, however, not infallible. More re- 
cent experiments made by Thompson with Marsh's apparatus, 
prove that antimony treated under the same circumstances, 
produce black metallic crusts upon porcelain. These stains, 
which at first sight might be confounded with those caused by 
arsenical preparations, are thus distinguished. 
1st. They only volatilize in part when exposed to a flame 
of pure hydrogen gas. 
2d. Heated with nitric acid they are transformed into anti- 
monious acid which undergoes no change by nitrate of silver 
in solution, whilst the spots of arsenious acid produce arsenic 
acid by this re-active, giving a precipitate of a brick red color. 
