Thallium. 
§§ 931,932.] 
721 
yield potassic chromate, soluble in water, and recognised by the red 
precipitate which it gives with silver nitrate, the yellow with lead 
acetate, and the green colour produced by boiling with dilute 
sulphuric acid and a little alcohol or sugar. If, by treating a com¬ 
plex liquid with ammonium hydrosulphide, sulphides of zinc, manga¬ 
nese, and iron are thrown down mixed with chromic oxide, the same 
principles apply. If a chromate is present in the contents of the 
stomach, and the organic fluid is treated with hydrochloric acid and 
potassic chlorate, chromic chloride is formed, and dissolving imparts a 
green colour to the liquid—this in itself will be strong evidence of the 
presence of a chromate, but it should be supplemented by throwing 
down the oxide, and transforming it in the way detailed into potassic 
chromate. 
A general method of detecting and estimating both chromium and 
barium in organic matters has been worked out by L. de Koningh. 1 
The substances are burned to an ash in a platinum dish. The ash is 
weighed ; to the ash is added four times its weight of potassium sodium 
carbonate and the same amount of potassium nitrate ; and the whole is 
fused for fifteen minutes. The fused mass is boiled with water and 
filtered ; if chromium is present, the filtrate is of a more or less pro¬ 
nounced yellow colour, but manganese may produce a green colour and 
mask the yellow; this colour is removed by boiling with a little 
alcohol. The liquid is concentrated down to 20 c.c., filtered into a 
test-tube, and a colorimetric estimation made of the chromium present 
by imitating the colour by a solution of potassium chromate of known 
strength. To prove that the colour is really due to chromium, acetic 
acid and lead acetate are added, when the yellow chromate of lead is 
at once thrown down. (If lead was in the ash, a yellow precipitate 
may appear on the addition of acetic acid.) To the portion of ash 
insoluble in water strong hydrochloric acid is added, and to the acid 
solution a large excess of calcium sulphate rs added ; this precipitates 
barium as sulphate free from lead sulphate, for, if the latter should 
be present, it does not, under the circumstances, come down, being 
soluble in strong hydrochloric acid. 
3. THALLIUM. 
§ 931. Thallium was discovered by Crookes in 1861. Its atomic weight is 204 ; 
specific gravity, 11-81 to 11-91 ; melting-point, 290°. It is a heavy diamagnetic 
metal, very similar to lead in its physical properties. The nitrate and sulphate of 
thallium are both soluble in water ; the carbonate less so, requiring about 25 parts 
of water for solution ; while the chloride is sparingly soluble, especially in hydro¬ 
chloric acid. 
§ 932. Effects. —All the salts of thallium are poisonous. One of the earlier 
experimenters on the physiological action, Paulet, found 1 grm. (15-4 grains) of 
4 (> 
1 Arch. Pharm. (3), xxvii. 944, 
