158 Intelligence and Miscellaneous Articles, 



the molecule of acid, I undertook a series of experiments to deter- 

 mine the true formula of tannic acid ; of these I now lay the results 

 before the Academy. 



To obtain tannic acid in a pure state, I purified the acid prepared 

 by the method of M. Pelouze, in two ways ; one portion was dis- 

 solved in pure aether and the solution precipitated by water, the 

 other portion was dissolved in water and precipitated by aether. 

 Under these conditions two or three distinct strata are obtained, of 

 which the heaviest consists of tannic acid, dissolved in the setherial 

 fluid. This syrupous liquid was dissolved in water and then evapo- 

 rated in vacuo ; the residue was analysed after being dried at 248° F. 

 Ten analyses made with oxide of copper in a current of oxygen gas 

 upon substances obtained at seven different preparations, gave results 

 leading to the formula C^* H^^ O^*. 



I. II. III. IV. V. VI. VII. VIII. IX. X. Calculated. 

 C 62-5 52-2 52-2 522 52-2 52-3 52- 1 52-2 52-3 523 54 = 52-4 

 H 3-8 3-8 37 37 36 39 3-8 36 37 35 22= 3-6 



34=440 



According to this formula, the resolution of tannic acid into gallic 

 acid and glucose may be represented by the following equation : — 

 C54H2«03^ + 8HOi=3(C'*H6 0>o)-|-Ci^^H»oo>o. 



This equation is confirmed by the quantities of the two compounds 

 obtained by the decomposition of tannic acid. The former was 

 found to be 87 per cent, (maximum) by Wetherill ; of glucose I 

 have obtained as much as 22 per cent. 



The quantity of water which may be displaced by metallic oxide 

 in the molecule C^* W^ O^* I have determined directly by digesting 

 tannic acid with oxide of lead, and the analysis of the neutral and 

 basic salts. By the former method I found that the acid loses 4*4 

 per cent., or 3 equivs. of water, which is confirmed by the analysis 

 of the salts of lead prepared by precipitation, in which the compo- 

 Bition of the anhydrous acid is represented by the formula C^^* H»» O'l, 

 differing by 3 equivs, of water from the formula C** H'^ O^*. The 

 precipitates obtained by tannic acid and acetate of lead contain from 

 3 to 10 equivs. of oxide of lead, in proportion to C**. The analyses 

 of tannates made by Pelouze, Liebig, Berzelius, Mulder and Biichner, 

 agree with the new formula of tannic acid, if we suppose that some 

 salts do not lose all their water at 212° F., or that they were not 

 completely dried. 



According to Berzelius, tannic acid combines with sulphuric or 

 muriatic acid, when these acids are added to a solution of tannic 

 acid in water. In these cases precipitates are obtained which are 

 dissolved at the commencement, until the fluid contains an excess 

 of sulphuric or muriatic acid. These compounds are distinguished 

 from the conjugate acids, as the mineral acid can be separated there- 

 from by salts of baryta or silver. The analysis of these precipitates 

 shows that they are nothing but tannic acid imbued with the acid 

 liquor in which they are deposited. In fact, this sulphuric tannin 

 only contains from 2 to 4 per cent, of sulphuric acid ; and the mu- 

 riatic tannin, when placed in vacuo over quicksilver, loses its muriatic 



