ABSORPTION OF SALINE SUBSTANCES BY CHARCOAL. 143 
The solutions of metallic salts upon which I operated are 
the following : — The acetate, sulphate and nitrate of copper ; 
the acetate, sulphate,chloride of zinc and oxide of zinc dissolved 
in ammonia ; acetate and nitrate of lead ; acetate and sulphate 
of iron ; tartar emetic ; the nitrate and sulphate of silver ; and 
the chloride dissolved in ammonia ; corrosive sublimate; ni- 
trate of cobalt ; sulphate of cadmium ; arsenious acid ; nitrate 
and muriate of baryta ; and the sulphate of soda, potash and 
magnesia. 
With the exception of the three alkaline sulphates, the ni- 
trate of copper and arsenious acid, which appear to be absorbed 
only within exceedingly restricted limits, all the other salts 
were absorbed with greater or less energy. 
5 parts of blood-charcoal calcined with potash sufficed to 
precipitate entirely the following salts ; acetate and nitrate 
of lead ; ammoniacal sulphate of copper ; the sulphate and 
nitrate of silver, and the chloride dissolved in ammonia ; the 
chloride of zinc, and oxide of zinc dissolved in potash. 
20 parts of charcoal are required to precipitate the sul- 
phate and acetate of copper, corrosive sublimate, nitrate of 
cobalt, sulphate of cadmium, tartar-emetic, sulphate of 
zinc, and choloride of barium. 
The precipitation, however is only perfect by the first 
five salts; and it appeared very difficult, even by increasing 
the proportion of charcoal, to remove entirely the last traces 
of the four others, which are it is true sometimes very mi- 
nute, but can still be detected. Thus the quantity of tartar- 
emetic which is not absorbed is so small, that its presence is 
no longer indicated by sulphuretted hydrogen : but it may 
still be discovered with Marsh's apparatus. 
The proportions of charcoal above indicated are only 
strictly accurate for the salts of copper; for the others they 
are only approximative; but they nevertheless approach very 
closely the true limits. The following is the plan which I 
followed to ascertain the quantity of charcoal necessary for 
the absorption of the sulphate and acetate of copper. I dis- 
