Dr Daubeny on separating Lime from Magnesia. IIS 
For this purpose, as well as for the sake of establishing more 
fully the facts already laid down, I took 50 gr. of crystallised 
Epsom salt, and exposed it in a platina capsule to the flame of 
a gas-lamp increasing the heat at successive intervals, and 
noting down the loss of weight each time. 
The moderate heat first applied, caused in half an hour a loss 
of 21.5 gr. or 43 per cent . ; but a continuance of the same for 
two hours drove off only 0.3 gr. more. I therefore increased 
the heat to the highest point which the gas-burner could afford, 
and found, that, at the expiration of an hour, the salt had lost 
2.1 gr. more, making the whole loss 23.9 gr. after which a con- 
tinuance of the same heat appeared to cause no farther change. 
Now, the quantity of water present in 50 gr. of crystallised 
sulphate of magnesia, amounts, according to the last experiment, 
(which agrees pretty exactly with other accounts), to 25.75 gr. ; 
so that nearly 6 per cent, of water was retained, after four hours 
exposure to the highest temperature that could be obtained in 
this manner. 
I then took the same quantity of the salt, and exposed it for 
a similar period of time in a platina crucible to a dull red heat, 
by which it was reduced from 50 to 23.7 gr. It had therefore 
sustained a loss of 26.3 gr. only 0.5 more than the quantity of 
water which the crystallised salt must have contained ; so that 
the heat applied in this instance may be presumed to approach 
as nearly as possible to that degree which was calculated (if any) 
to expel the water, without driving off the acid. 
Nevertheless, I found that the solubility of the salt was in 
this instance considerably affected ; for 10 gr* of the residuum, 
heated in a tube with twelve times its weight of water, were only 
partially dissolved. So altered, indeed, in this and other of its 
properties, did the salt appear, that it is probable that more of 
the acid had been driven off than the difference between 26,3 gr. 
* The gas- lamp promises to be an instrument of great utility in chemical re- 
search, and will almost supersede the employment of oil-lamps, in situations where 
a supply of the former can be readily obtained. Its advantages are, the great range 
of temperature which it affords, from 90° to 100° Fahr. to a greater heat than can 
be obtained by any oil-lamp, — its steadiness, and continuance for any length of 
time, — its safety, and cleanliness. 
VOL. VII. KO. 13. JULY 1822, 
H 
