106 THE CANADIAN NATURALIST. [March 



ducts artificially prepared by calcination possessed, like the natural 

 pozzuolanas, the power of rendering pure limes hydraulic ; but the 

 true mode of their action, which has not hitherto been understood, 

 i.s now rendered intelligible by this investigation of Fr^my. — 

 (Compfess Rendus de I' Acad, des Sciences, Dec. 21, 1868.) 



In this connection may be mentioned the peculiar power of 

 hardening under water presented by imperfectly calcined dolo- 

 mites or magnesian limestones. By heating these to a temper- 

 ature of 400°-500° centigrade the double carbonate is broken 

 up ; and the magnesia, losing its carbonic acid, remains mixed with 

 the carbonate of lime, but when moistened with water, is converted 

 in a few hours into a crystalline hydrate, which gives to the mass a 

 great degree of hardness. In like manner a condensed form of 

 magnesia, such as is obtained by calcining at a gentle heat, the 

 native anhydrous carbonate, gradually assumes, by the action of 

 water, a great degi-ee of hardness. T. s. H. 



On the Decomposition op Granite by Water. (R. 

 Hausmann, Jour, fur Prakt. Chem.) — The granite employed in 

 these experiments was reduced to a powder so fine that it had a 

 diameter of not more than 0.01 milUmeter. This digested for a 

 week, with twenty-five times its weight of pure water, at the ordinary 

 pressure and temperature, yielded an amount of soluble alkali equal 

 for 100 parts to 0.03 or 0.04, and when the mixture was kept in 

 continual agitation, to 0.05 parts. A longer digestion did not sen- 

 sibly increase the amount of matter dissolved. The solvent power 

 of water, saturated with carbonic acid, was found to be about twice 

 that of pure water. Calculating from the surface exposed in these 

 experiments, the author concludes that the rains of a year would 

 remove about fifteen grammes of alkalies from a surface of 100 

 square metres of granite. t. s. h. 



OxYCHLORiD OP CopPER. — Hydrous oxychlorid of copper, to 

 which the name of atacamite is given, is abundant in some regions, 

 especially in Chili, where it is supposed to be formed by the action 

 of sea-water on oxydizing copper pyrites. A late experiment of 

 Prof. Church throws further light on the origin of this com- 

 pound. He found that two grammes of the native blue hydrous 

 carbonate of copper, azurite, after four years digestion in 200 

 cubic centimeters of a solution holding ten per cent of pure chlorid 

 of sodium, had lost the whole of their carbonic acid, and become 



