
PRODUCTS OF DECOMPOSITION OF COMENIC ACID. 233 
The crystals contain further six atoms of water, according to one experiment, 
16-794 grains air-dry substance lost at 240° Fahr. 
3°709 ... water, 
which gives for 100 parts, 22-08 ; the number 22°53 is that required by the formula 
MgO, HO, C,, H, O,, 2HO+ 6 aq. 
Neutral Comenate of Magnesia.—When an alkaline ammoniacal solution of 
comenic acid is added to a solution of sulphate of magnesia, a salt is precipi- 
tated, especially on stirring the fluid, in the form of hard crystalline grains, 
adhering very much to the sides and bottom of the vessel. Under the microscope, 
those grains are found to be made up of groups of short prismatic needles. They 
are insoluble in boiling water. They lose their water of crystallization at 212°, 
but only after long exposure to that heat; thus dried they give the following 
results on analysis :— 



5°680 grains dried at 212° gave 
7-305 ... carbonic acid, and 
1-387... water. 
5'422 grains dried at 212° gave 
3115 ... sulphate of magnesia. 
Experiment. Calculation. 
aa 
Carbon, . i 35°07 34:89 C.. 72 
Hydrogen, a 2°53 2-42 H, 5 
Oxygen . c Soe 42-66 OF 88 
Magnesia, ; 19°53 20:03 2MgO 41-34 
100-00 100-00 206-34 
from which it appears that the formula expressing the composition of the salt, 
dried at 212°, is 
2Mg0, C,, H, 0,+3 HO. 
I endeavoured, by employing a higher temperature, to obtain a salt corre- 
sponding with the neutral salts of lime and baryta, in the amount of water 
retained at the same heat; but in the experiment I made, the substance lost 
weight at 250° gradually through a space of four days, and then the loss between 
each weighing was very small. It yielded 21:3 per cent. of magnesia, which ‘is 
more by a half per cent. than is required by a salt of the constitution sought for. 
The neutral comenate of magnesia, precipitated as above mentioned, has the com- 
position expressed by the formula 
2 MgO, C,, H, O,, 3HO +8 aq. 
the eight atoms aq. being lost at 212°. 
15-103 grains air-dry substance lost at 212° 
4003... water. 
This experimental number, calculated for 100 parts, gives 26:50; the number 
calculated from the above formula is 25°86. 
VOL. XX. PART Il. 3R 
