102 § '^1. BASES AND ACIDS WITH EE AGENTS. 



this Standard solution and one of acetic acid of known 

 strength. For this purpose add a measured quantity of 

 the standard sulphuric acid to a solution of sodic acetate, 

 but not enough to decompose the whole of the acetate. 

 Each cubic centimetre of the sulphuric acid, containing 

 0.04 grm., will set free an equivalent quantity of acetic 

 anhydride, = 0.051 grm., or of the hydrated acid, 0.06 grm. 



Knowing, then, how much acid has been set free, we can 

 titrate the mixture with the standard sodic solution, and 

 learn how much acetic acid each cubic centimetre of the 

 sodic solution will neutralize. 



Merz recommends the use of a tincture of turmeric as 

 a coloring matter that is not affected by neutral sodic ace- 

 tate ; the addition of a single drop of the soda solution to 

 a solution of sodic acetate colored yellow by this tincture 

 produces a brown color, while a drop of acetic acid re- 

 stores the yellow color. ( 'Wa(/7ier''s J'ahresbericht, 13, 498.) 



TARTARIC ACID. Il2C4H40fl. 150. 



71. Tartrates of barium, calcium, zinc, and copper, are 

 difficultly soluble in water. 



Reactions. — When tartrates are heated, they are black- 

 ened, and an odor of burnt sugar is given off. 



If a solution of free tartaric acid, that is not too dilute, 

 is mixed with a solution of potassic acetate, a crystalline 

 l^recipitate, KHC^H^Og, is formed at once, or after some 

 time, or after violent agitation, or addition of an equal 

 volume of alcohol. If the two solutions are very concen- 

 trated, and are stirred in a watch-glass, a deposition of 

 crystals marks the track of the rod over the glass. 



Calcic chloride gives a white precipitate, CaC^H^Og, in 

 solutions of a neutral tartrate, the formation of which is 

 hastened by violent agitation ; the presence of ammonic 

 chloride only retards the appearance of the precipitate, 



