ON CITRATE OF^MAGNESIA. 
219 
is that in which the taste peculiar to the base is to the 
greatest extent lost. 
Citric acid, which appears to have the property of thus 
modifying the taste produced by the base with which it may 
be combined, is obtained in several states. It contains 
sometimes three, sometimes four, and sometimes five atoms 
of water. 
According to Liebig, the formula for citric acid, such as 
it is met with in combination with oxide of silver, is C 12 H 5 
Crystallized citric acid, dried at 212°, contains C 12 H 5 O u 
+ 3 H 0=Ci + 3 HO. 
If it be crystallized from a boiling solution, it will contain 
C 12 H s O u + 4 H 0; and if crystallized by spontaneous 
evaporation at 68° Fahr., its composition jviil C 12 H 5 O n -f 
3 H + 2 H 0=Ci + 5 H 0. 
Citric acid is a tribasic acid, it forms with bases neutral 
salts, acid salts, and basic salts. 
In the neutral salts, each atom of acid is combined with 
three atoms of base. These salts are represented by the 
following formula : Ci, 3 MO + Aq. Their composition, is, 
therefore, analogous to that of the acid, with four atoms of 
water. The water of hydration in these salts may be re- 
placed by an atom of metallic oxide, when basic salts are 
formed. These have an atom of water of crystallization, 
which they lose at common temperatures, as the salt of sil- 
ver, or at a higher temperature. They are therefore ana- 
logous to the acid with five atoms of water. The composi- 
tion of the basic salts when dried, is CT, 3 M -f M 0. 
The citrate of magnesia, which forms the subject of this 
notice, is a salt but little known, being scarcely mentioned 
by chemists. Liebig, in his Traite* de Chimie Organique, 
merely says, "tylagnesia, alumina, and protoxide of man- 
ganese, form, with citric acid, neutral insoluble salts, and 
soluble salts which are acid." 
