200 M. Berzelius on the Combinations of [Sept. 



process similar to that by which epigenous crystals are pro- 

 duced in the mineral kingdom : it was easy to conceive that 

 since the salt of protoxide retains its solid form during the 

 whole period of its transformation, the constituents of the com- 

 pound into which it is finally changed might be held together 

 mechanically in very different proportions from those in which 

 they would naturally combine, when enjoying a state of com- 

 plete freedom. 1 had previously ascertained that when verdi- 

 gris is distilled in close vessels with a very slowly augmented 

 heat, there is obtained at a certain period of the process a 

 white sublimate, which sometimes fills the cavity of the retort 

 with a light aggregation of crystals, resembling wool. This 



sublimate is anhydrous acetate of protoxide of copper (Cu A). 

 I attempted, by exposing it to a moist atmosphere, to convert 

 it into a compound containing the acid and base united in the 

 same manner as in verdigris, but it underwent no alteration. 

 When kept in water, it is decomposed, hydrate of protoxide of 

 copper separating in the state of a yellow powder, and neutral 

 acetate of peroxide of copper passing into solution, in propor- 

 tion as the salt of protoxide absorbs a maximum of oxygen from 

 the atmosphere. 1 stratified thin plates of polished copper with 

 pulverized neutral acetate of peroxide of copper made into a 

 paste with water, and exposed the whole for two months to an 

 atmosphere which was constantly changing, but taking care, 

 during the whole of that period, to preserve the mass in a state 

 of saturation with moisture. At the conclusion of the experi- 

 ment, the metallic plates were found covered with an incrusta- 

 tion of small, silky, shining, blue-coloured crystals of the blue 

 variety of verdigris ; and these, being separated and dried in 

 the open air, yielded precisely the same analytical results as the 

 verdigris which occurs in commerce. This result totally refutes 

 the idea of an epigenous formation of verdigris, and demon- 

 strates that copper, with the assistance of acid and water, 

 acquires the property of combining with the previously formed 

 neutral salt. 



It appears to me not unlikely that the opinion of Proust, who 

 regarded verdigris as a compound of the neutral salt with 

 hydrated- peroxide of copper and water of crystallization, may, 

 perhaps, prove the most accurate. I have already endeavoured 

 to show that the blue carbonate of copper (azure copper ore) is 

 composed of an atom of hydrate of peroxide of copper, and two 

 atoms of neutral carbonate of copper ; and also that the artifi- 

 cial carbonate of zinc and magnesia alba are both analogous 

 compounds of hydrate and carbonate.* More recently, an 

 English philosopher f has discovered a blue crystallized mineral 



* Afh. i Fysik, &c. vi. 12, et seq. 



t Brooke, Annals of Philosophy, Aug. 1822, p. 118. 



