278 ANNUAL OF SCIENTIFIC DISCOVERY. 



solution of chloride of calcium and magnesium, and submitted it to the action 

 of a good red heat. After several repetitions of the process, the mass 

 became spongy and more absorbent. Pulverized, and raised to a white heat, 

 it fused to a milk-white mass, consisting of interlaced chrystalline fibres. Its 

 specific gravity was 3'0; it was not attacked by acids; it contained no chlo- 

 rine, but consisted of 



Si 5G-0 Ca 2G'3 Mg 17'7 



equivalent to (Ca, Mg) 3 Si2, or a variety of pyroxene. L' Institute, No. 1282. 



RESEARCHES IX LIME, SALTS OF LIME, AND MAGNESIA, AND ON THE 

 FORMATION OF GYPSUMS, MAGNESITES, AND DOLOMITES. BY T. 

 STERRY HUNT, F. R. S. 



In these researches, undertaken to clear up several obscure points in 

 Chemical Geology, the author shows, among other things 



1. The action of dilute solutions of bicarbonate of soda, added by de- 

 grees to liquids which, like sea-water, contain both salts of lime and mag- 

 nesia, determines at first the separation of all the lime as a nearly pure 

 carbonate, after which there is found a very soluble bicarbonate of magnesia, 

 which separates from concentrated solutions as a hydrous carbonate. 



2. Carbonate of lime, as is well known, requires for its solution about 

 1000 parts of water, saturated at the ordinary pressure with carbonic acid ; 

 but its solubility is much augmented by the presence of sulphates of soda 

 or magnesia : in which case there is formed a bicarbonate of soda or mag- 

 nesia, together with sulphate of lime, which may be precipitated by alcohol. 

 When a solution of bicarbonate of lime, mingled with sulphate of magnesia, 

 is evaporated at a gentle heat, crystalline gypsum is first deposited, while 

 bicarbonate of magnesia remains in solution, and is separated, as the liquid 

 is concentrated by evaporation, in the form of hydrous carbonate. 



3. When heated under pressure to 300 or 400 F., the hydrous carbonate 

 of magnesia is com'erted into a sparingly soluble crystalline, anhydrous 

 carbonate, which is magnesite; but if the amorphous hydrated carbonate is 

 mingled with carbonate of lime and then heated,, the two combine to form 

 a double carbonate, which is dolomite. 



In Haidinger's famous experiment, which was supposed to prove the 

 formation of dolomite by the reaction, at 400 F., of a mixture of sulphate 

 of magnesia and carbonate of lime, no double salt is formed; but a mix- 

 ture of carbonate of lime and magnesia is readily separated by dilute acids. 

 In Marignac's process, where chloride of magnesium replaces the sulphate, a 

 portion of double carbonate is, however, formed, and remains mingled with 

 magnesite and carbonate of lime. 



4. Besides the gypsums of epigenic origin, there are probably others 

 which have been formed by the simple evaporation of liquids like sea-water, 

 but the greater number of stratified gypsums are associated with magnesian 

 rocks, a fact which is readily explained by the reactions indicated above. 



Mr. Hunt considers attentively the various facts presented in the history of 

 magnesian limestones, and rejecting entirely the theory which ascribes their 

 formation to a metamorphism of sedimentary limestones, maintains that 

 they have been produced by the chemical union of carbonates of lime and 

 magnesia, which were deposited in a state of mixture from the waters of 

 seas and lakes. The carbonate of magnesia has either been produced by 



