CHEMICAL SCIENCE. 171 



minerals belonging to the spinelle group, several were obtained by the 

 author in his previous memoir ; the experiments, however, have been 

 repeated, and with better success as regards the size and perfection of 

 the crystals obtained. Magnesian spiuelle AP O 3 MgO, was prepared 

 by igniting a mixture of alumina, magnesia, chroniate of potash and 

 boric acid, the mixture remaining in the furnace eight consecutive 

 days. The crystals thus produced were octahedrons, truncated upon 

 the twelve edges, some of them three or four millimetres on the side ; 

 they were transparent, of great lustre, and of a more or less marked 

 rose color. The angles measured, perfectly corresponded to the theory ; 

 the density of the crystals was 3.542. Gahnite, Al 3 O 3 ZnO, chromite 

 of manganese, and other minerals of like character, have been also 

 obtained in equal perfection. Rutile was obtained in long acicular 

 prisms by igniting a mixture of titanic acid with phosphate of soda 

 and ammonia ; the crystals were transparent and of a golden yellow 

 color ; their density was 4.283, which agrees with that of rutile. 

 Annalles de Chimie, xxxiii. 34. 



ON THE FORMATION OF DOLOMITE BY THE ACTION OF MAGNESIUM 



VAPORS. BY M. DUROCHER. 



PIECES of a porous limestone and anhydrous chloride of magnesium 

 \vere introduced into a gun-barrel, so that neither substances were in 

 contact. The closed tube was then exposed for three hours to a dull 

 red heat, in order to maintain an atmosphere of chloride of magnesium 

 vapor round the limestone. At the end of that time the pieces of 

 limestone were found to be covered with a crust of fused chloride of 

 calcium and chloride of magnesium, mixed with a little peroxide of 

 iron, and the oxides of the two earths. The chlorides were separated 

 by washing with water, and the nuclei were then found to be partially 

 converted into dolomite. Transparent groups of crystals were visible 

 under the microscope ; the mass had a white color passing into yellow 

 and grayish-yellow, and was, like dolomite, full of cavities. Du- 

 rocher is of the opinion, that the assumption of some geologists, that 

 dolomite has been formed naturally by aqueous agencies, is proved by 

 this experiment not to be absolutely correct, as it may also have been 

 formed by magnesian vapors, issuing from the interior of the earth, 

 and gradually converting limestone into dolomite. Comptes Rendus. 



ON THE CHANGES IN STRUCTURE OBSERVED TO TAKE PLACE IN SOLID 

 ARSENIOUS ACID AND OTHER SOLID BODIES. 



THE most remarkable property of arsenious acid is this, that as an 

 amorphous body, without any admixture, and without losing its solid 

 state, it experiences a change which makes it assume a totally differ- 

 ent aspect. It has long been known, from experiment, that the trans- 

 parent arsenic glass gradually becomes opaque, until it resembles 

 porcelain. The substance, at first colorless, becomes white, the trans- 

 parency disappears, and it becomes completely opaque ; the beautiful, 

 vitreous lustre becomes feeble, and approaches the waxy. The specific 



