54 T. S. Hunt on Lime and Magnesia Salts. 
hydrated salts. A paste of magnesia alba and bicarbonate of 
soda with water was found to be slowly changed at a tempera- 
ture of from 60°-70° C. into transparent crystals of the anhy- 
drous double carbonate, which crystallizes in the hexagon | 
system and as remarked by Deville may be regarded asa soda- 
dolomite C,NaMgO,. I have already shown, § 38-40, that 
when this is heated to 200° C., with a solution of chlorid of 
calcium, the sodium is replaced by calcium, and dolomite is 
formed. It was with the anticipation that under conditions 
similar to those made use of by Deville, it might be possible 
to obtain double carbonates of lime and magnesia, that the fol- 
lowing experiments, resulting in the production of hydrated . 
carbonates, were undertaken. | 
$82. The first step was to procure a solution of the chlorids 
of calcium and magnesium in equivalent proportions, and for 
this purpose a crystalline dolomite from Galt, in western Canada, . 
whose only impurity was a few thousandths of carbonate of iron 
was selected. This being dissolved in hot hydrochloric acid . 
nearly to saturation, a little chlorine or chlorate of potash was 
added, and the digestion continued with an excess of the dolo- 
mite till the whole of the iron was precipitated, and a pure con- 
centrated solution of the two chlorids in equivalent proportions 
was obtained. 
§ 83. When the above solution is mixed with a slight excess ) 
of a solution of pure monocarbonate of soda and the resulting 7 
pasty mass heated to from 65° to 80° C., the precipitate is 
wholly changed in a few hours into a dense white granular 
matter, which, under the microscope, is seen to consist of pearly 
translucent globules, either single or aggregated. They areusu- ~ 
ally about ,,',;th of an inch in diameter, and although most | 
frequently spherical, sometimes present the form of disks hav- 
ing a radiated structure and ragged edges. Lobed and com- 
pound shapes from the coalescence of these disks are also met 
with. This substance is so slowly attacked by cold dilute aceti¢ 
acid that it was at first mistaken by me for true dolomite, an 
described as such in a note to the American Philosophical Society 
before I had discovered water in its composition. It, however, 
gives off an abundance of water when heated in a glass tube, 
even after having been dried at 85°C. In the analysis of three 
several preparations of this compound, in which the lime and 
magnesia were calculated as neutral carbonates, there was always 
a deficit of from seven to nine per cent, which was regarded as 
altogether water. In a subsequent preparation, however, it was 
fee 
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