lyiit Historical Sketch of the Physical Sciences, 1818. 
been made by chemists to discover a perfectly correct method of 
separating these two earths when they happen to occur together, 
as is the case in magnesian limestone, &c. I have mentioned 
some of these methods in the Annals of Philosophy, xii. 393. 
It was supposed that a solution of bicarbonate of potash poured 
into a muriatic or nitric solution of the two earths would precipi- 
tate the lime and leave the magnesia in solution. Buchblz 
demonstrated that this method is inaccurate, a portion of the 
lime being retained in solution, while a portion of the magnesia is 
precipitated. 
Tae method proposed by Dobereiner is nearly similar-to that _ 
practised long-ago by Vauquelin, and occasionally practised by 
others. It consists in pouring carbonate of ammonia into the 
solution of these two earths ; the carbonate of lime he assures 
us will be precipitated, while the magnesia forms a triple salt, 
and will be retained in solution. This method has been shown 
by Pfaff to be inaccurate. A part of the magnesia is always 
precipitated along with the lime. 
Pfaff considers the best method of separating the two earths 
to be to neutralize the solution, and then to precipitate the lime 
by oxalate of ammonia. Mr. Phillips informs us, however, that 
the lime is never precipitated by this reagent till enough of the 
oxalate has been added to form a triple salt with the magnesia. 
In employing this method to separate the lime from sea-water, 
which | have frequently done, I have often been surprised at the 
slowness with which the lime was precipitated in such cases; 
but I have never examined whether the whole lime was precipi- 
tated. Indeed from the weight of the precipitate thus obtained, 
[ think there is reason to suspect that a portion of the magnesia 
is prcwEaies as well as of the lime. 
mentioned in the number of the Annals o Philosaphy above 
quoted the method which I had been in the habit of employing 
to separate these two earths from each other. I dissolve the 
two in muriatic or nitric acid, and add to the solution a sufficient 
quantity of sulphuric acid to decompose the muriates or nitrates 
formed. This mixture is now evaporated to dryness, and exposed 
to a heat sufficiently high to drive off the excess of sulphuric 
acid, if any be present. The dry mass is now digested in water 
to dissolve the sulphate of magnesia, and the water is mixed with 
a little alcohol to diminish the solubility of the sulphate of lime. 
By this method I have often obtained results which did not 
deviate materially from the truth. 
Mr. Phillips has suggested a modification of this process, 
which I have not hitherto tried; but which promises to be an 
improvement. He dissolves the mixture of the two earths in 
muriatic or nitric acid ; but instead of adding sulphuric acid, he 
adds sulphate of ammonia in sufficient quantity to convert the 
muriates or nitrates into sulphates. The sulphates thus formed 
are weighed. The mass is then digested in a saturated solu- 
7 
