COLOURING MATTERS IN WINE. 209 



which no trace of tannic acid shall be found, as some 

 .little is always absorbed, either from the skins or the 

 wood of the casks, the wine-grower's experience 

 teaches him that the wine will remain white in pro- 

 portion as it is excluded, from the very first, from the 

 air, which is necessary to the formation of apothema of 

 tannic acid. All this agrees exactly with what we said 

 of the cause of the yellow colour of liqueur wine. 



I have, I believe, represented the cause of the colour 

 of wines which are not red, in the simplest possible 

 form, and freed it from the obscurity which encom- 

 passed it, so long as we were taught that every shade 

 of colour, in white or liqueur wines, was to be ac- 

 counted for by a peculiar colouring matter. In truth, 

 there are at most only two colouring matters, both 

 apothemata, one of tannic acid, and one of the soapy 

 matter. 



Madeira and Teneriffe wine were precipitated with 

 sugar of lead, and filtered. A faintly coloured yellow 

 liquid, which could not be attributed to the apothema 

 of tannic acid, was obtained. Its intensity did not 

 amount to one-tenth of the colour of Madeira or 

 Teneriffe. This yellow tinge can be ascribed only to 

 those mixed organic substances which render wine 

 extract so dark after evaporation. One of its con- 

 stituents is apothema of extractive matter. 



The precipitate of sugar of lead, which is brown, 

 contains principally the colouring matters of Madeira 

 and Teneriffe. If it be suspended in water, and sul- 



p 



