42 THE GRAPE. 



stance in treating of liqueur- wines. At present we 

 will only observe, that raisins prepared from white 

 grapes cease to be white, and become light brown, 

 the reason being that atmospheric action has changed 

 the tannic acid contained in the skins into apothema, 

 a brown substance. It is not, however, by the pro- 

 cess of drying that the skins acquire a brown colour, 

 for if they are softened in water they do not regain 

 their original hue, but remain brown. 



If the raisin skins are well soaked first in water, 

 and then in liquid ammonia, so as to remove all tannic 

 acid, a quantity of apothema is obtained from the 

 tannic acid as a brown substance dissolved in am- 

 monia. 



I may here observe, that the contents of white 

 raisins are no longer as they were originally, " colour- 

 less," but (in consequence of a peculiar change in 

 one of the ingredients of grape juice, called extrac- 

 tive matter) are transformed into a brown substance, 

 and coloured brown. 



We shall speak more particularly of this point in 

 treating of the colour of liqueur- wines. 



The other component of grape-skins is the colouring 

 matter which exists in purple grapes, and is the only 

 cause of the colour of red wine. 



Colouring matter is obtained from grape-skins in 

 the following manner : they are well washed in water, 

 then soaked in water and acetic acid, precipitated 

 with sugar of lead, the precipitate washed, suspended 



