Intelligence and Miscellaneous Articles. 389 



water, and introduced into the compartment destined to receive and 

 absorb the gas evolved by the action of tartaric acid upon bicar- 

 bonate of soda placed in the other compartment ; the apparatus is 

 then closed. 



After several days of digestion, the liquid, saturated with carbonic 

 acid and retaining in solution a certain quantity of the oxide with 

 which it had been in contact, is decanted, and left to spontaneous 

 evaporation, either in the open air or in loosely stopped bottles. The 

 hydrated carbonates are then deposited very slowly, either in the 

 form of pulverulent flakes, or in more or less distinct crystals, some- 

 times several millimetres in diameter. In this way the author has pro- 

 duced a hydrated carbonate of magnesia in large and perfectly trans- 

 parent crystals, by digesting in water charged with carbonic acid, a 

 mixture of carbonates of lime and magnesia obtained by precipitating 

 a neutral liquid containing dolomite dissolved in nitric acid by car- 

 bonate of ammonia. The water dissolved carbonate of lime and a 

 still larger quantity of carbonate of magnesia. When exposed to 

 the air it deposited from the very first day small acicular crystals of 

 carbonate of lime ; then the liquid being reduced to about a sixth of 

 its original volume by spontaneous evaporation in the open air for 

 about two months, it gave crystals of hydrated carbonate of magnesia. 

 These crystals of several millimetres in diameter are derived from an 

 oblique rhomboidal prism, presenting the same angles observed in 

 the hydrated carbonate of magnesia, MgO, C0'- + 4Ag., described 

 by Marignac. Exposed to a slight heat these crystals lose a part of 

 their water, and become opake. They contain no lime. 



Water charged with carbonic acid dissolves considerable quan- 

 tities of protoxide of iron, and peroxides of zinc, lead, silver, and 

 copper ; the latter gives the liquid a fine sky-blue colour. These 

 solutions were left for several months to spontaneous evaporation ; 

 some of them deposited carbonates in pellicles or amorphous flakes, 

 others exhibited some microscopic crystals. — Comptes Rendus, March 

 16, 1857, p. 561. 



NOTE ON A NEW CYANOMETER. BY FELIX BERNARD, 

 If it be true that the proportion of polarized light contained in a 

 ray emanating from a determinate point in the sky varies with the 

 transparency of the atmosphere, and consequently with the brilliancy 

 of its tint, it is however not evident, that, as has generally been 

 admitted hitherto, these two quantities vary in the same proportion ; 

 the measuring instruments founded upon the proportionality of these 

 two elements can, therefore, only lead to results of doubtful exacti- 

 tude, and this doubt must remain as long as this question is unsolved 

 by experiment. On the other hand, if this agreement were com- 

 pletely established, the employment of one of these means exclusively 

 would be insuflScient for the study of the laws of atmospheric polar- 

 ization, as these must be deduced from observations made in perfectly 

 definite circumstances. These considerations have led me to intro- 

 duce some very simple modifications into the polarimeter, which I 

 have already submitted to the Academy of Sciences*, and these 



* Comptes Rendus, October 23, 1P54. 



