214 



adstringent taste and of acidulous reaction ; is insoluble in volatile 

 and in fixed oils, its alcoholic solution precipitates the glue, not 

 the tartarated antimony, greens chloride of iron ; throws down a 

 red powder when digested hot with diluted acids. 



TsmuiCOlticipinic Acid =0-28 H13 O12. Known in the bark of 

 Pinus sylvestris from 20-25 years old trees. Boil with alcohol of 

 40%; distil the alcohol completely from the tinctui-e, remove a 

 viscid resin from the remnant by filtering, precipitate the filtrate 

 with acetate of lead, wash the deposit and add subacetate of lead 

 to the filtered licpiid, obtaining thereby a deposit, which contains, 

 like the first, Tannicorticipinate of lead. Treat the deposit, pro- 

 duced by acetate of lead, three times with acetic acid, but avoid 

 to dissolve the whole ; free from the undissolved portion containing 

 resin, by filtration, precipitate the liquids with subacetate of lead, 

 collect the deposit, wash and decompose under water with sulphuret 

 of hydrogen. The liquid, fi-eed hj filtering from the sulphuret of 

 lead and evaporated to half its volume in a current of carbonic acid 

 gas, forms brown-red crusts of the T. acid. B. — Decompose the 

 deposit, obtained by subacetate of lead, under water with sulphuret 

 of hydrogen, evaporate the filtrate in a current of carbonic acid 

 gas, dissolve the remnant in alcohol, precipitate with alcoholic 

 acetate of lead, wash and decompose the deposit under water with 

 sulphuret of hydrogen, evaporate the filtrate in a current of car- 

 bonic acid gas, and dry at 100°. — Reddish-brown powder of 

 astringent taste, colours chloride of iron — at first dark-green, 

 aftei'wards red-brown, and produces at last a black-green deposit; 

 yields a red product by heating with diluted acids. 



Tannic Acids, Derive their name from one of their generally 

 known properties, viz., of tanning animal membrane, i.e. of con- 

 verting it into a durable compound, called leather. They are also 

 distinguished by their faculty of forming with glue compounds 

 more Or less soluble in water ; by theii* acid reaction towards 

 litmus-paper ; by their astringent, but not acid, taste ; by their 

 amorphous condition ; by their property of forming deejD-blue or 

 green, sometimes brown, compounds with Lron oxyd or with iron 

 oxyd-suboxyd, not with pure iron suboxyd ; and by their disposi- 

 tion to decompose in aqueous solutions and under access of the ah- 

 and more readily so in the presence of alkalies. 



The number of Tannic acids is very large, but of theii* chemical 

 constitution we know as yet little or nothing. This accounts for 

 the confusion which prevails in regard to their classification. 

 Provisionally they are generally divided into acids which blue, 

 and into those which green the iron-salts ; but the colours of the 

 liquids or of the deposits which are produced by the mutual action 

 of these bodies and of iron-salts vaiy for one and the same sub- 

 stance, according to the state of Oxydation of the iron, and are also 



