CLEAEING or WINE. 95 



form a spongy flocculent sediment, by means of which 

 a larger or smaller quantity of colouring matter, in 

 proportion to the quantity of albumen or isinglass which 

 has been applied, is withdrawn from the wine. 



Clearing may also be undertaken in order to di- 

 minish the tannic acid contained in the wine ; and this 

 again is effected by means of albumen and isinglass. 



For when both these substances are added to port 

 wine, tannic acid and colouring matter are continually 

 abstracted from it, so that by adding them in large 

 quantities, tannic acid may be entirely withdrawn, 

 and a very light-coloured wine be obtained. 



The colour of wine, in which but little tannic acid 

 is contained, can only be abstracted by adding a solu- 

 tion of tannic acid, previous to the addition of albu- 

 men or isinglass, in which case, so large a quantity 

 of colouring matter is precipitated, as to render the 

 wine very light coloured. Albumen and isinglass 

 alone could not have effected such a change. The 

 cause of this phenomenon will be made quite clear 

 when we come to treat of the colour of wine ; for 

 colouring matter is soluble in alcohol and tartaric 

 acid, and more or less so in water and tartaric acid. 

 The chemical affinity which exists between the par- 

 ticles of colouring matter, and such albumen or glu- 

 ten as has been precipitated by means of alcohol and 

 tannic acid, is more or less overcome by the power, 

 which a mixture of water, alcohol, and tartaric acid 

 possesses of retaining colouring matter in solution. 



