ON SOLUTION OF CITRATE OF MAGNESIA. 
217 
ordered in the officinal formula, and moreover, does not affect the 
transparency of the solution, it has some advantages and merely 
adds a little citrate of potassa to the solution. The officinal 
solution contains, theoretically, 21,5 grains, or about 47 cubic 
inches of carbonic acid gas, while the solution occupies the space 
of 21 cubic inches. 
The process of the pharmacopoeia, when the carbonate of 
magnesia is pure and free from grit, is upon the whole nearly unob- 
jectionable, for making the solution extemporaneously. Whenever 
the carbonate is impure, the last portion added, leaves a sediment 
in the solution. It requires, however, more time — at least half an 
hour being requisite to effect the solution of the last addition of 
carbonate. 
When calcined magnesia is employed with pure citric acid the 
solution rarely needs filtering, and the small proportion of bicar- 
bonate of potassa, as the source of the carbonic acid, dissolves so 
soon that a bottle can be prepared for use in a few minutes. The use 
of calcined magnesia, however, is by no means free from objection. 
I have recently ascertained that magnesia, having all the external 
characters of a good preparation, contained 25 per cent, of volatile 
matter, the larger part of which was water. Here, then, is a source 
of inequality in the strength and taste of the solution, it being much 
more acid at one time than another, according to the purity of the 
magnesia employed. 
The quantity of (pure) calcined magnesia, equivalent to five 
drachms of carbonate is 125 grains, according to Fownes, and 134 
grains according to Berzelius ; the carbonate I have tried recently, 
corresponds more nearly with the constitution given by Berzelius 
than Fownes. 
Although an aeid solution will keep better than a neutral one, 
yet there are therapeutical objections to the presence of much 
acidity in it, which should prevent the apothecary from rendering 
the preparation permanent at the expense of its usefulness. 
