588 poisons : their effects and detection. [§ 767. 
lieated, when the arsenic will sublime on to the glass disc, partly as a 
metal and partly as crystalline arsenious acid. With minute films of 
metallic arsenic it is, however, better by means of a small pointed 
flame to draw out the tube on both sides of the arsenical ring, and seal 
it ; the sealed tube is then heated in a bath of ordinary solder to about 
400° C. The oxygen of the enclosed air unites with the arsenic at 
once ; the crystals are formed without any possibility of loss. 
3. Arsenious acid, itself inodorous, when heated on charcoal, after 
mixing it with moist oxalate of potash, evolves a peculiar garlic-like 
odour. To this test oxide of antimony adulterated with arsenic will 
respond, if there is only a thousandth part present. Simply projecting 
arsenious acid on either red-hot charcoal or iron produces the same 
odour. 
4. A little bit of arsenious acid, heated in a matrass with two or 
three times its weight of acetate of potash, evolves the unsupportable 
odour of kakodyl. 
5. A good test for arsenious acid in organic free solutions is a solution 
of stannous chloride in ether. The stannous chloride solution B.P., 
shaken up with ether, gives a fairly strong ethereal solution of stannous 
chloride. If a solution of arsenious acid to which HC1 has been added be 
shaken up with this ethereal solution of stannous chloride and heated 
to 40° C. for a few minutes, at the junction of the liquids a yellowish- 
brown colour appears, and the ethereal layer is tinted more or less yellow. 
With small quantities, such as under a milligramme, the ether is coloured, 
but the yellow-brown disc is not present (de Jong, Zeit. f. anal. Chem., 
1902). 
Arsenites and Arseniates, mixed with oxalate of soda and heated in 
a matrass, afford distinct miirors, especially the arsenites of the earths 
and silver ; those of copper and iron are rather less distinct. 
Sulphides of Arsenic are reduced by any of the processes described 
on p. 611 et seq. 
In Solution. An acid solution of arsenious acid gives, when treated 
with SH 2 , a canary-yellow precipitate, soluble in ammonia, carbonate of 
ammonia, and bisulphite of potash, and also a metallic sublimate when 
heated in a tube with the reducing agents in the manner described at 
p. 587. By these properties the sulphide is distinguished and, indeed, 
separated from antimony, tin, and cadmium. 
The sulphides of tin and cadmium are certainly also yellow, but' the 
latter is quite insoluble in ammonia, while the former gives no metallic 
sublimate when heated with reducing substances. 
The sulphide of antimony, again, is orange, and quite insoluble in 
potassic bisulphite, and scarcely dissolves in ammonia. 
A small piece of sodium amalgam placed in a test-tube or flask con¬ 
taining an arsenic-holding liquid, or the liquid made alkaline with soda 
