1824.] Acelic Acid with Peroxide of Copper. 197 



scales. On being examined, it was found to possess exactly 

 the same composition with the salt last analyzed. 



This sub-salt I have besides obtained by still different pro- 

 cesses. For example, when hydrated peroxide of copper is 

 macerated for some hours in a solution of the neutral acetate, 

 it is converted into a light-grey coloured, heavy, pulverulent 

 powder, which, when taken from the liquid and washed, 

 becomes green. If a concentrated boiling hot solution ot 

 acetate of copper be mixed with caustic ammonia, with the 

 precaution that no excess of the alkali be added, we obtain a 

 heavy granular precipitate, of a dull greyish green colour, and 

 which is uncommonly easily washed. Under a microscope this 

 compound appears to consist of transparent, cubical crystals, 

 having their corners rounded off. When heated, they decrepi- 

 tate. °All these dissimilar varieties, when treated with sulphuric 

 acid, yielded 129-4 parts of sulphate of copper for every 100 

 parts of the dried salt : they all appeared therefore to consti- 

 tute the same sub-acetate. 



This combination, therefore, is the most easily formed, and 

 possesses the best defined composition of all the sub-acetates of 

 copper. The acetic acid is combined in it with thrice as much 

 oxide as in the neutral salt. Since in this salt, the oxygen of the 

 water of crystallization is only one half of what is contained by 

 the peroxide of copper, I attempted, by digesting sub-sulphate 

 of copper in a solution of acetate of soda, to produce an analo- 

 gous compound, in which the oxygen of the water and of the 

 oxide would be equal ; but no mutual decomposition took place 

 between the two salts. 



In the three salts now analyzed we have found, therefore, that 

 the oxide of copper combines with the acetic acid in the multi- 

 ples in which bases usually combine with acids containing 

 3 atoms of oxygen, namely, 1, 1*6, 3. What is the constitution 

 of verdigris ? 



3. Verdigris. 



Verdio-ris occurs in commerce under very different appear- 

 ances ; sometimes it is green, sometimes it is bluish green, and 

 very frequently it has a beautiful blue colour. Sometimes it 

 dissolves in acetic acid, without leaving ar:y residue of mecha- 

 nically intermixed impurities, while, on other occasions, it 

 leaves undissolved a considerable quantity of protoxide of cop- 

 per. In general, however, we may refer it to one or other of 

 two principal varieties, the green and the blue. These colours 

 are most accurately distinguished, when the compounds are in 

 the state of powder. What difference in the processes of ma- 

 nufacture occasion this dissimilarity in appearance, I have been 

 unable to discover ; because I procured the specimens for my 

 experiments from merchants who were ignorant of the places 



