162 CHYMISTRY APPLIED TO AGRICULTURE. 



excess of tartaric acid ; when exposed to the air upon cloths 

 they acquire a brilliant whiteness. 



Froria this last combination tartaric acid may be extracted 

 by the following process, for which we are indebted to 

 Scheele. Dissolve cream of tartar in boiling water, and 

 saturate the solution with chalk ; a precipitate of lime com- 

 bined with the acid will be thrown down ; this must be 

 separated, and sulphuric acid poured upon it in the propor- 

 tion of one third of the weight of cream of tartar employed ; 

 to this mixture apply a gentle heat for ten or twelve hours ; 

 the sulphuric acid will combine with the lime and form an 

 insoluble precipitate, whilst the tartaric acid will be set free 

 and swim above it ; the whole must then be diluted with 

 cold water, and the liquor filtrated and evaporated to the 

 consistency of a sirup, when the tartaric acid will be pre- 

 cipitated in a concrete state. When evaporation is carried 

 on slowly and the sirup allowed to remain at rest, the acid 

 crystallizes in long octahedrons : if these crystals be purified 

 by being repeatedly dissolved, and the solution filtrated and 

 evaporated, they become very white, and present the form of 

 tetrahedral prisms, terminated by pyramids of four elongated 

 faces. 



Tartaric acid is composed of 



Carbon 24.050 



Oxygen 69.321 



Hydrogen 6.629 



One of the acids most extensively found in the vegeta- 

 ble kingdom is the malic ; this differs essentially from 

 the two of which I have just spoken, in remaining always 

 in a liquid state, and forming with lime a salt soluble in 

 water. 



Malic acid may be procured by saturating the juice of 

 apples with potassa, and decomposing the salt thus formed 

 by means of the acetate of lead : the precipitate thus pro- 

 duced must be washed, after which sulphuric acid must be 

 poured upon it till the liquor retains no sweetish taste : an 

 insoluble sulphate of lead is formed, which may be separated 

 from the malic acid by filtration. Scheele, by whom this 

 acid was discovered, has made many experiments to ascertain 

 its existence in vegetables. 



Malic acid is found most abundantly in apples, barberries, 

 plums, and sour grapes ; red fruits furnish less of it, but it is 

 found in a greater or less quantity in nearly all the products 

 of vegetation. 



