ACETATES AND THEIR MANUFACTURE. 283 



state of acetate of suboxide of copper. Crystallized verdigris is 

 occasionally employed as a transparent green water color or wash 

 for tinting maps. In medicine it is used for external application. 

 It is poisonous like all soluble copper salts. 



Basic cupric acetates. Sesquibasic cupric acetate (Cu(C 2 H 3 O 2 ) 2 ) 2 

 CuO + 6H 2 O. This compound is obtained pure by gradually 

 adding ammonia to a boiling concentrated solution of the normal 

 acetate until the precipitate, which is at first formed, is redis- 

 solved. As the liquor cools the new salt then crystallizes out in 

 beautiful blue-green scales, which at 212 F. lose 10.8 per cent, 

 of their water. Their aqueous solution is decomposed by boiling, 

 acetic acid being given off and the black oxide of copper pre- 

 cipitated. 



Dibasic cupric acetate, Cu(C 2 H 3 O 2 ) 2 CuO 4- 6H 2 O, constitutes 

 the greater part of the blue variety of verdigris. It forms beau- 

 tiful, delicate, blue, crystalline needles and scales, which when 

 ground form a fine blue powder. When heated to 140 F. they 

 lose 23.45 per cent, of water and become transformed into a 

 beautiful green, a mixture composed of the neutral and tribasic 

 acetates. By repeated exhaustion with water the dibasic is re- 

 solved into the insoluble tribasic salt, and a solution of the nor- 

 mal and sesquibasic cupric acetates. 



Tribasic cupric acetate, Cu(C 2 H 3 O 2 ) 2 2CuO -f 3H 2 O. This 

 compound is the most stable of any of the acetates of copper. It 

 is prepared by boiling the aqueous solution of the neutral acetate, 

 by heating it with alcohol, by digesting its aqueous solution with 

 cupric hydrate, or by exhausting blue verdigris with water, as 

 mentioned above. The first methods yield the salt in the form 

 of a bluish powder composed of needles and scales, the last as a 

 bright green powder. This salt gives off all its water at 352 

 F. ; at a higher temperature it decomposes and evolves acetic 

 acid. Boiling water decomposes the solid tribasic acetate into a 

 brown mixture of the same salt with cupric oxide. 



Under the name of verdigris two varieties of basic cupric 

 acetate are found in commerce : French verdigris which occurs 

 in globular, bluish-green, crystalline masses, but also in amor- 

 phous masses, and English verdigris of a pure green color and 



