190 M. Berzelkis on the Combinations of [Sept. 



conformity to it absolutely necessary. Consequently, when 

 any exception to the generally admitted rule appears to have 

 been discovered, it deserves, before it be finally admitted as 

 such, to be studied with the deepest attention, and to be con- 

 firmed by the most careful and intimate examination. A confir 

 matory examination which I undertook of an exception of this 

 nature, gave cause to the present memoir. Mr. K. Phillips * 

 has examined the sub-acetates of copper which occur in com- 

 merce under the name of verdigris ; and it follows from his 

 experiments, that the oxygen of the acetic acid is 1-L time that 

 of the peroxide of copper, which is at variance with the above 

 cited empirical law respecting the compounds of oxidated 

 bodies. 1 have therefore studied the combinations of acetic 

 acid with this base, and believe that the results which I have 

 obtained are not altogether destitute of interest. 



Before detailing my own experiments, I shall briefly relate 

 what had been previously made known respecting these combi- 

 nations. Chaptal endeavoured to investigate the difference 

 between the verdigris manufactured in the neighbourhoods of 

 Montpellier and of Grenoble, which are prepared by dissimilar 

 methods, and are distinguished by dissimilar shades of colour. 

 His examination was conducted by submitting them to dry dis- 

 tillation, and he found the one variety to contain a larger quan- 

 tity of copper than the other ; but his experiments left the pro- 

 portions of the constituents of verdigris wholly undetermined. 



Proust undertook a more complete investigation. He ascer- 

 tained that in the salt saturated with acetic acid, the oxide of 

 copper constitutes 39 percent.; but he could not determine 

 with certainty the relative quantities of the acid and of the 

 water of crystallization. He at first regarded the verdigris 

 which we find in commerce as a mixture of two distinct salts, 

 one of which is soluble in water, while the other is not. The 

 former he found to constitute 056, and the. latter 044 of the 

 weight of the verdigris. The insoluble salt, also, he found to 

 consist of 063 of oxide, and 0-37 of acid and water. Some 

 time after he altered his opinion respecting the constitution of 

 verdigris, partly on the ground that it is decomposed by water; 

 partly that, when diffused through water, a current of carbonic 

 acid gas decomposes it into neutral acetate and carbonate of 

 copper, and partly that when boiled with water it deposits black 

 oxide of copper. The last mentioned property induced him to 

 consider verdigris as a combination of neutral acetate of cop- 

 per and hydrate of peroxide of copper, which is decomposed 

 by boiling. He found in it 0*47 of neutral salt, 023 of oxide 

 of copper, and 0*30 of water ; quantities which agree very 

 closely with the results of more recent analyses. 



* Annals of Philosophy, N. S. vol. iv. p. 161. 



