282 
ON THE DETECTION OF ARSENIC. 
smoke, with a characteristic alliaceous order. This odor, clue 
to a portion of arsenic reduced by the contact of charcoal, is 
not manifested when the arsenious acid is placed upon a red 
hot 'brick, it then volatilizes without sensible odor. This 
acid is sparingly soluble in water; hot water dissolves more than 
cold water; at +15° it dissolves JjjL and at +100° ^ so that 
a part of the acid separates in a crystalline form by the cooling 
of the solution. 
Composition. 
Arsenic 75.82 or 2 atoms ) Its formulae 
Oxygen 24.18 or 3 " 5 is As 
100.00 
Distinctive Characters. 
1st. Reduced to fine powder, and thrown upon glowing 
charcoal, the arsenious acid is at once disengaged in the form 
of white vapors of an alliaceous odor, leaving no residue 
upon the charcoal. If during its volatilization you place with- 
in two inches of it a bright plate of copper, the vapors con- 
dense upon it, giving a white coating to the metal, but if the 
plate is held too near the fire, say within a line or two, you 
obtain a black or grayish coat. 
The blackish color developed in the latter case, depends 
(according to Orfila) upon a portion of metallic arsenic depo- 
sited upon it, and which being reduced by contact with the 
charcoal, condenses upon the plate previous to being burnt by 
the oxygen of the air. (Jour, de Chimie Med. et de Tox. 
vol. 5th.) 
2d. Dissolved in boiling water, its solution feebly reddens 
tinctureof litmus. Lime water addedinexcessoccasionsawhite 
precipitate of arsenite of lime, soluble in an excess of acid; 
hydosulphuric acid communicates to it a golden yellow color, 
which a small quantity of ammonia causes to disappear, and 
which the acids re-establish, forming a flocculent yellow pre- 
cipitate of sulphuret of arsenic. 
If you abandon to itself the solution mixed with hydrosul- 
phuric acid it becomes after sometime turbid, and deposits yel- 
