114 Dr Daubeny cm separatmg Lime from Magnesia. 
the amount of the loss sustained, and ^5.75, the proportion of 
water originally present; so that it seems not unfair to conclude 
that the acid begins to be expelled before all the water is sepa- 
rated, and that in this instance a portion of the latter was still 
retained. 
In order to learn how much further the weight of the salt 
might be affected- by increase of temperature, I exposed the re- 
siduum for two hours to a stronger heat than had been before 
employed, and detected at the end a further loss of weight, 
amounting to 10 grains for the whole quantity. 
Submitted for two hours longer to the same temperature, the 
weight of the salt was diminished by 3.3 ; but it appeared to 
have parted with nearly all the acid which could be separated 
by heat, as three hours continuance in the same temperature 
caused a further diminution of scarcely 0.7 gr. 
The residuum, weighing just 10 grains, appeared to be wholly 
insoluble in water, but was entirely taken up by muriatic acidy 
emitting, however, during the time that the solution was going 
on^ a smell of sulphuretted hydrogen, which seemed to indicate, 
that, contrary to the received opinion, sulphate of magnesia is 
convertible into a sulphuret by a continued heat. 
Thus, it appears, that crystallised sulphate of magnesia loses 
at least 80 per cent, of its weight, when exposed for some time 
to a high temperature ; but that it retains to the last a portion. 
of its acid, was evident from the cloud caused in the muriatic 
solution, by adding a few drops of muriate of barytes, although, 
as TOO gr. of the crystallised sulphate contain about 16 of base, 
We cannot estimate the quantity of acid higher than at about ^ th 
of the whole. It would appear by Berzelius’ statement, that 
magnesia is precipitated from its solutions in sulphuric and mu- 
riatic acid by ammonia, in the state of a suhsalt^ and not of a 
pure hydrate ; but he rates the proportion of acid in these cases 
much lower, for in the subsulphate he found magnesia 67.5 per 
cent..) sulphuric acid 1.6, water 30.9. 
The experiments just detailed, seem to establish the truth of 
the facts jWhich I mentioned, as calculated to throw considerable 
doubt upon the exactness of Mr Phillips’ method ; but I flatter 
myself that the objections may be obviated by the following 
simple addition to the process he has recommended. Having 
