( 30 ^ ) 
Art. XVIII . — On the Methods of separating Lime from Mag-- 
nesia. By C. Daubeny, M. D. M. G. S. (Concluded 
from p. 123 .) 
I INFER, therefore, that the plan proposed by Dr Wollaston 
for ascertaining the presence of magnesia, may, under proper 
management, be safely extended to the determination of its 
quantity, where no other substance is present ; but it was still a 
question, whether the remark held good, when any considerable 
portion of a salt of lime had been originally present. 
That, under the latter circumstances, the precipitate afforded 
by phosphate of soda would be somewhat less than what could 
be obtained from the same quantity of the magnesian salt un- 
mixed, seemed a necessary consequence of what I had already 
ascertained as to the precipitation of a portion of that base by 
carbonate of ammonia, when lime was present ; but it was also 
possible, that as a certain portion of the latter earth escaped the 
action of the re-agent, and remained in the supernatant liquor, 
the affinity of the magnesia for it might interfere with the effect 
of the phosphate of soda upon that base. 
It was impossible to try this experiment fairly in the case of 
sulphate of magnesia, as the sulphate of lime is too sparingly 
soluble, to be employed in sufficient quantity, and the nitrate or 
muriate would decompose the magnesian salt. I therefore re- 
solved to ascertain what proportion of a given weight of mag- 
nesia could be recovered by the application of phosphate of soda 
to a solution of the earth in muriatic acid, when a definite quan- 
tity of muriate of lime was present, compared to what could be 
precipitated by the same re-agent, when the magnesia was em- 
ployed unmixed. 
I made several experiments to this effect, but I believe I can 
best depend on the four following : 
Per Cent, 
1. Of 10 gr. of Magnesia recently calcined, I recovered, by means 
of Phosphate of Soda, - - - - 945 
2. Of ditto with 10 gr. of Lime, - • - 85.2 
S. 10 gr. of Carbonate of Magnesia, . - ^ 80.5 
4. Ditto with 10 gr, of Carbonate of Lime, • - 77.6 
From the loss experienced in these and other attempts to re- 
cover the quantity of base which had appeared to have been 
