226 MR HENRY HOW ON CERTAIN SALTS AND 
fully into the relations between it, which was now named Comenic Acid, Meconic 
Acid, and Pyromeconic Acid, the product of dry distillation common to both the 
former bodies. The subject was further discussed by Dr Srennouse,* in a paper, 
to some of the details of which I shall have occasion to refer. 
I employed for the preparation of comenic acid the process of RopiqueT as 
modified by GreGory, which consists in boiling crude meconate of lime (or, still 
better, the acid salt obtained by once treating this substance with boiling water and 
hydrochloric acid) with a quantity of pretty concentrated hydrochloric acid suffi- 
cient to dissolve it. For the purification of the acid which is deposited in the 
form of very dark-coloured hard crystalline grains, SrenHouUsE recommends solu- 
tion in a slight excess of caustic potass or soda, and recrystallization of the salt 
deposited from the boiling fluid. I preferred, however, to use ammonia, since, if 
certain precautions are adopted, a salt is obtained as readily deprived of colour as 
the potass salt, and much more insoluble in cold water than the corresponding 
salt of soda; while the mother liquors afforded a convenient means of trying the 
action of various chemical agents upon the acid. The process I employed consists 
in boiling the dark-coloured grains in water, with gradual addition of caustic 
ammonia, till the whole is in solution. The fluid is then immediately filtered. 
The addition of an excess of ammonia, and the continuance of a boiling heat are 
to be avoided, as there ensues, if this be not attended to, a curious decomposition, 
attended with the production of much colouring matter, the explanation of which 
will be entered into subsequently. 
The ammonia salt obtained as above, deposits from the black fluid in yellow 
hard crystals if the solution is left at rest, but in soft silky prisms when it is agi- 
tated; in the latter state the salt is not so readily washed free of the coloured 
mother liquor. By two or three crystallizations from boiling water, a salt of 
dazzling whiteness, in fine radiated four-sided prisms, is obtained. 
From solutions of this salt, which, when even quite pure, have a faint shade 
of straw-colour, the addition of concentrated hydrochloric acid throws down co- 
menic acid in the form of a white heavy crystalline powder adhering to the sides 
of the vessel, which, when dissolved in boiling water, in which it is not very so- 
luble, is deposited from a saturated solution in grains and crusts, almost colour- 
less; but as the solution cools, groups of short prismatic, or sometimes leaf-like, 
crystals appear, always possessing a characteristic yellowish-red tinge of colour. 
The general chemical and physical properties of comenic acid have been already 
too well described to require any special remarks on my part; I shall therefore 
proceed at once to the details of the salts I have examined. 
Bicomenate of Ammonia. 
This salt was obtained and analysed by StennousE, who formed it by solution 
* Mem. and Proc. Chem. Soe., vol. 1. 
EE a 4 
