102 Prof. Louis Henry on the Polymerization 



d. Cu. Two basic hydrocarbonates of copper are natural 

 compounds, viz. malachite and azurite, but both may be 

 produced artificially. 



CuC0 3 . CuO . 2H 2 0. 

 CuC0 3 . CuO . H 2 (Malachite) . 

 2CuC0 3 . CuO . H 2 (Azurite) . 



e. Co and Ni. 



' by precipitating a cobalt salt 



2CoC0 3 . 2Co(OH) 2 + 5H 2 0-{ by alkali carbonate in the 



cold, 

 the preceding precipitate 

 2CoC0 3 . 3Co(OH) 2 + H 2 after washing at a boiling 



heat. 



H 2 i 



n nr\ on rr\Tj\ ,ua f the same boiled with carbo- 

 CoC0 3 .3Co(OH) 2 + H 2 J nate0 f S0da>&c . 



by precipitating nickel sul- 

 2NiC0 3 . 3Ni(OH) 2 + 2H 2 ^ phate with sodium carbo- 

 nate in the cold. 



As a general rule these precipitates become more and more 

 basic as the temperature of precipitation is higher, and, like 

 the corresponding hydrates, they become decarbonated and 

 dehydrated under a more or less intense heat. The cause 

 which determines the molecular complexity of these com- 

 pounds, the accumulation of the metallic radicals in the same 

 product, leads as a final result to a true oxide. The produc- 

 tion of a simple monometallic oxide HO* by the action of 

 heat, would consequently compel us to assume, that at a given 

 moment an effect was produced quite contrary to all that had 

 preceded it. 



Nitrates, Sulphates, and Chlorides. — The following phe- 

 nomena are quite analogous to that which we have just 

 examined. We have seen that certain carbonates, formed 

 in the presence of water, are partially decomposed by the 

 latter, with the formation of a hydroxide, and the final 

 production of a basic hydrocarbonate, the radical C0 3 

 being replaced by HO. The nitrates, sulphates, and chlo- 

 rides of certain metals, notably those whose oxides are 

 feeble bases, undergo a similar change in the presence of 

 water. A salt originally neutral in composition is first con- 

 verted into a basic salt, and finally, under the action of heat, 

 in the presence of a large quantity of water (either alone or 

 slightly alkaline), into a true oxide. Thus : — 



Mercuric Nitrate Hg(N0 3 ) 2 , under the action of cold water, 

 gives a basic trimercuric nitrate Hg(N0 3 ) 2 . 2HgO, which 



