54:6 Intelligence and Miscellaneous Articles. 



thrown great light on the controverted question of the formation of 

 dolomites and the general problem of metaraorphism. 



The author conceived the idea of forming certain mineral species 

 in the humid way, and his first essays were made with the carbonates. 

 As it is clearly demonstrated that heat generally favours dehydra- 

 tion, it occurred to the author that the formation of neutral car- 

 bonates might be a simple question of pressure and temperature ; but 

 before attempting to precipitate them by the disengagement of the 

 excess of carbonic acid serving them as a solvent at a high tem- 

 perature under strong pressure, the author attempted double decom- 

 positions in the humid way. These first attempts set out there- 

 fore from the beautiful experiments of M. Haidinger. 



The substances were exposed to each other in glass tubes, herme- 

 tically sealed, after having exhausted them. If they were of a kind 

 to react upon each other immediately, they were at first separated, 

 and were then by turning moved at the proper time. For high 

 temperatures the tubes were inclosed in a gun-barrel, hermetically 

 sealed and half-filled with water, so as to equalize as much as possi- 

 ble the internal and external pressures on the glass tube. The tubes 

 were heated in small closed chambers in the furnaces of a gas-work. 



The following mineral species were by these means produced : — 



Carbonate of Magnesia. — ^By the double decomposition of sulphate 

 of magnesia and carbonate of soda, at about 322° Fahr. It was in 

 the state of white crystalline sand, which was scarcely acted upon 

 by weak acids. Having understood, during the course of his experi- 

 ments, that M. Maurignac had performed analogous experiments on 

 the reaction of chloride of magnesium and carbonate of lime, hereafter 

 to be described, the author did not proceed further. 



Carbonate of Protoxide of Iron. — Obtained by double decomposi- 

 tion : first, of sulphate of protoxide of iron and carbonate of soda, 

 at about 302° F. and above ; second, from protochloride of iron and 

 carbonate of lime, at temperatures between 266° F. and 392° F., 

 kept up during twelve, twenty-four, and thirty-six hours. The 

 carbonate of iron was in the state of crystalline sand, of greater or less 

 fineness, of a grayish-black colour, nearly unalterable in dry air, very 

 slowly acquiring a flaxen colour in moist air, and scarcely acted upon 

 by diluted acids. This crystalline sand has then all the properties 

 of spathose iron ore. Its gray colour is more or less dark, and its 

 spontaneous alterability is the smaller according as it is formed at 

 high and long- continued temperatures. Perhaps to circumstances 

 of this kind may be attributed the differences which exist in this 

 respect among natural spathose iron ores ; differences which are not 

 sufficiently explained by variation in their composition. 



Carbonate of Manganese. — Obtained by double decomposition : 

 first, of chloride of manganese and carbonate of soda, at about 320° F. ; 

 second, chloride of manganese and carbonate of lime, at tem- 

 peratures between 284° F. and 338° F., kept \yp twelve and forty- 

 eight hours. It is in the state of a fine white powder, slightly rose- 

 tinted, no crystalline appearance, and is unalterable at a moderate 

 heat. 



Carbonate of Zinc. — Obtained under the same conditions as that 

 of iron ; it is a fine white powder, not crystalline, unalterable at a 

 moderate heat. — Comptes Rendus, Juin 4, 1849. 



