214 ON SOLUTION OF CITRATE OF MAGNESIA. 
ON SOLUTION OF CITRATE OF MAGNESIA. 
By William Procter, Jr. 
The extensive use now made of Solution of Citrate of Magne- 
sia by physicians, and the favorable reception it has met at the 
hands of the medicine-taking community, and above all, its adop- 
tion in the last edition of the Pharmacopoeia, are strong evidences 
of its real merits as a refrigerant and cathartic. The want of 
permanence of the solution, as frequently sold, however, has been 
the cause of disappointment to the patient, and of loss and annoy- 
ance to the pharmaceutist. 
This change manifests itself by the gradual deposition of a white 
granular powder, which continues until sometimes the bottles are 
half filled with the sediment. The object of this paper is to ex- 
plain the nature of this change, and to point out, if possible, a 
means of avoiding it. 
Citric acid is what chemists call a tribasic acid, that is to say, 
it combines with one, two, or three equivalents of abase, so as to 
form three distinct classes of sails. It contains three equiva- 
lents of basic water besides its water of crystallization, and in 
uniting with a base to form a salt, this water is partially or wholly 
displaced by the base, according as one, two or three equivalents 
of the latter enter into combination. Citric acid contains one equi- 
valent of water of crystallization, if deposited from a hot solution, 
and two equivalents if from a cold solution, by spontaneous evapo- 
ration. The commercial acid is the former, and its formula is 
C l2 H 5 O u , 3HO+ HO. Brande states that citric acid of this 
constitution does not lose weight or transparency when exposed 
to a temperature of 212°, but that the acid containing two equi- 
valents of water, by exposure to the same heat, loses all its water 
of crystallization. 
1. One hundred grains of citric acid was dissolved in 700 grains 
of distilled water, and recently calcined magnesia carefully added 
to it until neutral to litmus. Thirty grains of magnesia was re- 
quired. This is in the exact ratio of three equivs. of base to one 
of acid 3MgO, Ci. This solution, after standing 24 hours, com- 
menced to deposit the white powder before alluded to, which ap- 
