1821.] Native Carbonate of Magnesia, 253 



tain it, I passed a fragment, weighing a few grains, into a jar 

 inverted over mercury, and let up a sufficient quantity of dilute 

 sulphuric acid, the full action of which required more than a 

 week. Carbonic acid was disengaged at the rate of M cubic 

 inch from every grain of the stone ; and reckoning 100 cubic 

 inches of carbonic acid at a mean temperature and pressure 

 = 46*5 grs. 100 grs. of the mineral would yield 51 grs. very 

 nearly of the acid gas. 



One hundred grains, reduced to powder and calcined in a suf- 

 ficient heat, lost 51*5 grs. A similar quantity being heated to 

 redness at the bottom of a long glass tube, the upper and cool 

 part of the tube just exhibited a visible degree of moisture, 

 which could not amount to nearly a grain in weight. 



One hundred grains were dissolved in heated and diluted sul- 

 phuric acid, with the exception of 1*5 gr. The insoluble part 

 was not acted upon by being boiled to dryness with nitromuriatic 

 acid, or with solution of potash, and when examined by a mag- 

 nifier seemed to me to be a fine siUceous sand. The solution 

 being evaporated, and the product heated to redness, gave 140 

 grs. of dry sulphate of magnesia, equivalent at 33 per cent, mag- 

 nesia to 46 grs. of that earth. 



One hundred grs. dissolved by an excess of nitromuriatic acid, 

 left the same proportion as before of insoluble matter. The 

 solution was evaporated to dryness, redissolved in water, and 

 part of the magnesia which had separated was again taken up 

 by muriatic acid, carefully added, so as to be very slightly in 

 exx:ess. From one half of the solution, subcarbonate of potash 

 precipitated, at a boiling temperature, carbonate of magnesia, 

 which, w^hen washed, dried, and calcined, gave 23 grs. of the 

 pure earth, equal to 46 grs. of magnesia, from 100 of the stone^ 

 The other half afforded, with a mixture of phosphate and carbon- 

 ate of ammonia, a precipitate which, after being heated to red- 

 ness, left 60 grs. of phosphate of magnesia, equivalent (if the 

 base in 100 grs. of that salt be reckoned at 38*5 grs.) to 25 grs. 

 of magnesia, or to 46 from 100 of the stone, thus confirming the 

 other methods of analysis. 



The absence of lime and alumine was inferred from the non- 

 action of the proper tests of those earths on a solution of the 

 stone in muriatic acid, rendered just neutral by ammonia. I am 

 aware, however, that a minute proportion oif lime, existing in 

 any solution along with a considerable proportion of magnesia, 

 is not discoverable by the usual tests. Of this, any person may 

 be satisfied by mixing a saturated solution of sulphate of lime 

 with an equal bulk of solution of sulphate of magnesia ; for the 

 mixed solutions are not rendered turbid by oxalate of ammonia, 

 either immediately, or on standing. It is possible, therefore, that 

 the mineral may contain a very small proportion of lime, though 

 I did not discover any by analysis. The muriatic solution 

 showed^ on applying the proper tests, a minute trace of iron. -, 



