SECT. xii. ACIDS. 419 



sublimes without alteration, but a strong heat de- 

 composes it. Nitric acid converts it into the 

 malic and oxalic acids. 



It is of great utility in the art of dyeing, and 

 forms the basis of all black colours and of colours 

 with a dark ground. It forms also the basis of ink ; 

 and chemists use it as a test to detect the presence 

 of iron. 



SUBSECTION Vl. 



fartarlc Acid. If wine is kept for a length of 

 time in a cask or other close vessel, a sediment is 

 precipitated which adheres to the sides or bottom, 

 and forms a crust known by the name of tartar, 

 which is a combination of potass and a peculiar 

 acid in excess. The compound is tartan te of 

 potass, and the acid in its state of purity is the tar- 

 taric acid. 



It is characterized by the property of its forming 

 with potass a salt that is soluble with difficulty. 



It has been found in the following vegetable sub- 

 stances also : in the pulp of Tamarinds, in the juice 

 of the Grape, and Mulberries, Sorrel, and Sumac ; 

 and the roots of Triticum repens> and Leontondon 

 Taraxacum. It is not much used except among 

 chemists. But the tartarite from which it is usually 

 obtained is well known for its medical virtues under 

 the name of Cream of Tartar. 



