204 PRECIPITATION BY ANIMAL CHARCOAL. 
in to such a degree, that the solution became only very slightly 
clouded upon the addition of water. 
3. Astringent Substances. — A solution of one grain of extract 
of nutgalls in half-an-ounce of water required twenty grains 
of charcoal ; a solution of half-a-grain of pure tannin dissolved 
in half-an-ounce of water required ten grains of charcoal ; an 
infusion of ten grains of rhatany root and the same quantity of 
cinchona bark in two ounces of water, required twenty grains 
of charcoal to deprive them of their power of reacting on the 
salts of iron. 
2. Inorganic Substances. 
That animal charcoal precipitates certain metallic salts from 
their solutions in water or spirit of wine, is a fact which has 
been long established. I find that probably all metallic solu- 
tions are similarly affected, though some require more charcoal 
than others. Moreover, this effect does not depend on the 
chemical constitution of the metallic oxide, whether its formula 
be MO or M 2 3 . 
The following salts were subjected to experiment:— 
Sulphate of copper Chloride of tin 
" zinc Corrosive sublimate 
u protoxide of iron Acetate of the oxide of iron 
" oxide of chromium Nitrate of nickel 
Nitrate of oxide of mercury " protoxide of cobalt 
Acetate of lead " silver 
Emetic tartar " protoxide of mercury 
On an average, thirty grains of charcoal were required for 
every grain of these salts, dissolved in half an ounce of water ; 
but, for reasons hereafter mentioned, it was difficult to precipi- 
tate them entirely, the addition of charcoal only rendering the 
reaction less distinct. 
If caustic ammonia be added to those salts whose bases can- 
not be precipitated by ammonia, or which are redissolved by 
excess of the precipitant (copper, zinc, silver, lead in sugar of 
lead) much less charcoal is required; and the precipitation takes 
place much sooner. Not merely basic metallic oxides, but also 
