394 Scientific Intelligence. [Nov. 



together in the same mineral ; as, for example, in magnesian 

 limestone. Many formulas have been proposed, but none of 

 them has been found to answer completely. I may mention one 

 or two of them by way of example. One of the oldest methods 

 is to dissolve the two earths in an acid and to pour into the so- 

 lution bicarbonate of potash. Lime does not readily form a bicar- 

 bonate, and the carbonate of lime is insoluble in water. Magnesia, 

 on the contrary, enters easily into combination with two atoms 

 of carbonic acid, and the bicarbonate is soluble in water. From 

 these facts the conclusion was drawn that the lime would be 

 totally precipitated while the whole of the magnesia would 

 remain in solution. This method was examined by Bucholz with 

 his usual precision ; and he has shown that it does not answer. — 

 (Schweigger's Jour. xvii. 56.) Dobereiner has proposed another 

 which, in his opinion, answers perfectly. It is to dissolve the 

 two earths in an acid, and to pour carbonate of ammonia into the 

 solution. The lime will be precipitated in the state of a carbon- 

 ate, but the magnesia forming a triple salt with the acid and the 

 ammonia will remain in solution. — (Ibid. p. 78.) This method 

 has been recently examined at great length by Professor Pfaff, 

 of Kiel. The result of his experiments is, that, besides the lime, 

 a portion of the magnesia is always precipitated by the carbonate 

 of ammonia. He found further that when a solution of sal-am- 

 moniac is boiled over a mixture of carbonates of lime and 

 magnesia, the magnesia is not alone dissolved, but also a portion 

 of the lime. This constituted a part of Dobereiner's method, 

 Pfaff examined also the double salts which magnesia and 

 ammonia form with the different acids ; and he found that the 

 proportion of these two bases differed materially according to the 

 acid with which they were combined. In sulphate of magnesia 

 and ammonia, in the nitrate, the muriate, and the acetate of 

 these bases, he found the proportion of magnesia and ammonia 

 to each other as follows : 



Magnesia. Ammonia. 



Sulphate 3 : 2 



Nitrate • 2 : 1 



Muriate 1 : 1 



Acetate 16 : 1 



Pfaff considers the best method -of separating lime from 

 magnesia to be to dissolve both earths in an acid, to neutralize 

 the solution, and then to precipitate the lime by means of oxalic 

 acid. — (Schweigger's Jour. xxi. 74.) The metlud which I 

 myself have been in the habit of employing for separating lime 

 from magnesia has the advantage at least of being very easy ; 

 and though not absolutely precise, the error, I believe, when the 

 experiment is rightly conducted, is very small. I dissolve the 

 mixture of lime and magnesia in muriatic acid, or nitric acid ; 

 then add to the solution a quantity of sulphuric acid capable of 



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