1X2 Dr Daubeny on separating Lime from Magnesiq. 
If, therefore, the real weight of the precipitate in the former in-^ 
stance be put at 19.^, it will stand in the latter at 14.97; for, as 
20.15 : 19.2 : : 15.7 : 14.97. 
Now, 14.97 of sulphate of barytes indicate about 5.1 of sulphu- 
ric acid, or 1.4 less than was present in the same quantity of 
salt, which had been exposed only to a heat of 212°. 
It is worth remarking, that 1.4 gi\ of sulphuric acid exceeds 
only by 0.05 the quantity that would be required to neutralise 
0.7 of magnesia, the exact amount of the residuum which the 
water did not take up. This residuum I treated with muriatic 
acid, which dissolved the whole of it ; and on adding muriate of 
barytes, I perceived a cloudiness, but so slight a one, that the 
quantity of sulphuric acid present was inappreciable from its 
minuteness. 
Upon the whole, therefore, these results confirm each other 
as nearly as can be expected, and lead to the inference, that if 
sulphate of magnesia be exposed to the heat of boiling water 
only, little more than half of its water of crystallization will be 
expelled ; and if, to insure the separation of the remainder, a 
more elevated temperature be made use of, the residuum is then 
resolved into two salts, the one probably a neutral sulphate, so-^ 
luble in water, the other a subsulphate, retaining but a minute 
proportion of acid, and nearly insoluble. 
This may perhaps be seen more clearly by the following com- 
parative sketch of the results obtained : 
20 grains of crystallised Sulphate of Magnesia, exposed to a temperature of 21 2“^ 
10.3 gr. of Water of Crystallisation^ 
Retained, - 4.74 J 
9.70 Dry Salt. 
20.00 
Ditto, exposed to a red heat. 
Lost, Acid, 1.4 
Water, 10. 
Retained, Acid, 5.1 
Magnesia, 3.2 viz. -j 
‘•Hn. 
).3i 
7 gr. 
a soluble sulphate, 2.5 
insoluble ditto, 0.7 
20.0 3.2 
It was desirable, however, to ascertain whether the heat might 
not be so regulated, with respect to duration and intensity, as 
to expel the whole of the water, without reaching the point at 
which the acid would be driven off. 
