110 Dr Daubeny cm separating Lime from Magnesia » 
Having now pointed out the general principles to which f 
allude, and referring to the facts that will be detailed in the 
course of this paper for a further illustration of it, I proceed to 
comment upon one of the oldest and most favourite methods of 
separating lime from magnesia, I mean, that of combining both 
with sulphuric acid, and availing ourselves of the different solubi- 
lity of the two salts thus formed, as a means of separating them. 
Of the formulas that have been recommended for this pur- 
pose, the one mentioned by Mr Phillips in the sixth volume of the 
Journal of Science,” appears to me the most satisfactory, and 
to this I intend to confine myself, conceiving that any objections 
that may be raised against his plan, apply with equal force to 
the methods proposed by other chemists, so far as they are de- 
pendent on the same general principle. 
Mr Phillips recom mends j that the earth suspected to contain 
magnesia should be dissolved in muriatic acid, that the muriates 
should be decomposed by sulphate of ammonia, the ammonia^ 
cal salts and water driven off by exposing the whole, after eva- 
poration, to a red heat, and the residuum, after this process, 
(considered as consisting merely of the sulphates of lime and 
magnesia,) treated with water already saturated with sulphate 
of lime, in order to dissolve the magnesian without taking up any 
of the calcareous sulphate. 
By these means, it is presumed, that the difference in the 
weight of the dried salt before and after the solution of sulphate 
of lime has been added, will give the proportion of sulphate of 
magnesia present, and that we may safely infer that of the cal- 
careous sulphate from the residuum after such addition. 
Ingenious as this process is, I shall state some objections it 
seems liable to ; the first knowledge of which I owe in a great 
measure to a paper published in the 1 2th volume of the Annales 
de Chimie, by M. Longchamp. 
It is directed by Mr Phillips, that the solution should be ex- 
posed, after the conversion of the muriatic salts into sulphates, 
to a temperature capable of expelling the ammoniacal salts and 
the water present. M. Longchamp, however, shews, that the 
fresh portion of a particular salt, with which it had previously become saturated, 
in consequence of the admixture of a new ingredient. 
