274 
ON DIFFERENT KINDS OF MAGNESIA, ETC. 
to prescribe the medicine of magnesia with the proportions 
I have indicated when it is to be taken in less than three 
days ; but that it will be necessary to increase the propor- 
tion of water when it has to be kept longer. 
The following, according to M. Gobley, is the formula of 
a draught of magnesia, which may be kept liquid for an 
indefinite period: — 
— Calcined magnesia, 8 
Syrup of orange flowers, 30 
Distilled water, 87 
I am now going to point out how it is that I have not 
observed solidification of oxide of magnesia in preparing 
my draughts: and, first, I might remark that the medicine 
of magnesia belonging to the class of medicaments prepared 
only when wanted, that is to say, magistral medicaments, I 
had not attended to its conservation ; but I can make no 
such excuse. Here is the truth. After having theoretically 
and practically proved that the presence of sugar in the 
magnesian draught greatly augments its efficacy, which, to 
me, was indisputably established some time before the 
publication of my formula, I made some experimental in- 
vestigations to ascertain whether all the varieties of cal- 
cined magnesia were equally adapted for suspension in 
syrup ; if all were equally miscible in that vehicle, and I 
soon ascertained that the light variety of calcined magnesia 
is best adapted for preparing the purgative draughts having 
oxide of magnesium for their base. Moreover, experience 
taught me that all the varieties of light calcined magnesia 
are not equally fit for employment in the preparation of 
white medicines. That which appeared to me to succeed 
the best, and to which, consequently, I give the preference, 
is a variety of oxide of magnesia generally well decarbon- 
ated, very white, which has been very common in com- 
merce for some years, and which is said to come to us from 
London. 
