ON DIFFERENT KINDS OF MAGNESIA, ETC. 275 
The medicines of magnesia prepared with the English 
calcined magnesia, of which I have just spoken, present the 
form of a white and very homogeneous liquid, of the con- 
sistence of a clear syrup, and may be kept liquid for an in- 
definite period. 
What was my surprise, after this description, to learn that 
the magnesian draughts prepared by M. Gobley had pre- 
sented to him totally different physical properties ! 
To what could the difference of our results be owing ? 
Was it to the chemical nature of the oxide of magnesia 
employed by me ? 
But my magnesia was pure: it did not contain even ap- 
preciable quantities of carbonic acid. 
Was it due to the presence of a certain quantity of water 
which the English decarbonated magnesia might, perhaps, 
contain ? 
I thought for some time that it must be thus, being con- 
vinced by analysis that this -English magnesia really con- 
tained water ; that it contained as much as 20 per cent, 
of its weight, that is to say, one-fifth. 
However, it was not to this that the difference of the 
results was owing ; for, having prepared a hydrate of mag- 
nesia similar to that of London, and having prepared with 
it a medicine of magnesia, the latter acquired, after seve- 
ral days, a consistence incomparably greater than English 
decarbonated magnesia takes under the same circum- 
stances. 
I wish for a moment to call the attention of practitioners 
to the intimate nature of the light calcined magnesia which 
comes to us from London, and which I will designate under 
the name of hydrate of magnesia, or better still, under the 
name of slaked magnesia. 
Hydrated or Slaked Magnesia. 
This commercial variety of decarbonated magnesia is 
very white, very light, very soluble in the acids, and con- 
