92 
THE TANNINS. 
Tannates are formed by addition of the acid to car¬ 
bonates or hydrates in the case of the alkalies, and to 
hydrates in the case of the alkaline earths. With the 
metals it forms tannates on its addition to an acetate. 
By certain precautions the purity of the salt may be 
improved,—for instance, by the use of alcoholic solu¬ 
tions in the preparation of the alkali salts. Sodium 
tanuate, JNaC 14 H 9 0 9 , and potassium tannate, KC 14 H 9 0 9 , 
are obtained as crystalline precipitates by adding an al¬ 
coholic solution of the hydrate to an alcoholic solution 
of tannic acid ; the precipitate dries to a fine powder. 
Barium tannate, Ba(C 14 H 9 0 9 ) 2 , is formed by pre¬ 
cipitating the sodium salt with barium chloride. An¬ 
other barium salt, of the formula Ba(OH)C 14 H 9 0 9 , is 
formed by adding barium carbonate to a hot aqueous 
solution of tannic acid. 
At least three lead salts are known. According to 
Pelouze and Strecker, the compound 3PbC 14 H 8 0 9 -f 
Pb(C 14 H 9 0 9 ) 2 + 2H 2 0 is formed by precipitating lead 
acetate with an excess of tannic acid. Strecker is also 
authority for the compound 2PbC 14 H 8 0 9 + Pb(OH) 2 
by precipitating tannic acid with an excess of lead 
acetate, and the compound Pb 3 (C 14 H 7 0 9 ) 2 -f 2Pb(OH) 2 
by heating an excess of lead acetate with a dilute tannic 
acid solution. Scliiff found two salts according as the 
tannic acid or lead acetate is in excess, an excess of the 
acid giving Pb 2 C 14 H 6 0 9 + 2H 2 0 and an excess of the 
lead salt giving Pb 3 C 14 IP 4 0 9 . The compounds with 
lead have probably been studied more than any of the 
other tannates, and many besides those given above 
have been described. 
The tannates of iron have also received a large share 
