TANNIC ACID Iff WINE. 193 



and the older the Port wine the more apparent is the 

 yellow colouring. This is a plain proof that the 

 yellow colouring matter did not originally exist, but 

 is afterwards formed in the wine. 



I obtained results like the above from analysing 

 the cake-like deposits of Port wine. They were taken 

 from very old Port wine, and had undergpne all the 

 alterations which were possible to them under the cir- 

 cumstances. 



It was first necessary to examine whether the 

 yellow colour of the old Port was attributable to these 

 substances ; that is, whether a small portion of them 

 was still held in solution in the wine. In order to 

 ascertain this, the above-mentioned deposit was 

 extracted with warm alcohol, it was sufficiently 

 soluble to impart to the liquid a colour which, when 

 cool, exactly agreed with that of Port wine. The 

 liquid, filtered from some of the insoluble consti- 

 tuents, was deprived of colour by means of basic 

 acetate of lead, and all the yellow substance com- 

 bined with oxide of lead. This lead precipitate was, 

 after being washed, suspended in water, and decom- 

 posed by means of sulphuretted hydrogen ; the water 

 passed through clear, whilst the sulphide of lead, 

 treated with boiling water, imparted to it a yellow 

 colour. 



The watery solution, when exposed to evaporation, 

 deposited a dark-coloured substance, soluble in water. 

 No precipitate was obtained from this solution when 



o 



