194 TA1O1C ACID IIS" WINE. 



mixed with solution of gelatine till after an acid Lad 

 been added, and then the whole of the brown sub- 

 stance was contained in the precipitate. 



Exactly the same substance may be obtained from 

 Port wine itself. Port wine was precipitated with 

 acetate of lead, the precipitate washed, suspended 

 in water, and sulphuretted hydrogen conducted 

 through it, and the liquid afterwards filtered. After 

 the sulphide of lead had been boiled with water, and 

 the solution evaporated, the addition of solution of 

 gelatine was not sufficient to produce a precipitate, but 

 it was necessary to add acid. The result obtained 

 was, that the yellow colouring matter of the Port 

 wine agreed exactly with a portion of the sediment 

 deposited in the course of time. 



These properties agree entirely with those which 

 Berzelius has published as peculiar to apothema of 

 tannic acid. Pelouze found that a diluted solution of 

 tannic acid becomes brownish yellow when exposed to 

 the air ; and any one who chooses to expose solution 

 o? tannic acid to the air, may, after a time, perceive 

 the alteration in the colour, which appears darker or 

 lighter according as the solution is more or less con- 

 centrated. This change is not, however, to be con- 

 sidered exactly the same as that which tannic acid 

 undergoes when exposed to heat ; for, at the usual 

 temperature, not only is colour changed, but gallic 

 acid formed, and the discoloration may be viewed as 

 partial decomposition of the sugar of tannic acid 



