THE “PHOSPHATE OF AMMONIA ” OF BRITISH PHARMACOPOEIA. 509 
the Pharmaceutical evening meeting, as being a subject which scarcely war¬ 
ranted such attention ; but'as Dr. Redwood at the last meeting of the “ Chemical 
Discussion Association ” seemed particularly to desire it, I have ventured, with 
some further analyses and addenda, to present it again this evening. That the 
field for criticism of the Pharmacopeia is almost exhausted, is obvious to any 
one who has read the ‘Pharmaceutical Journal,’ or analogous transactions; 
still one or two minor subjects remain which might be investigated, though, 
even their investigation is of no particular importance, either in a chemical or 
medical point of view. Now, as regards some substances, the statements of the 
Pharmacopoeia could only be called in question by a practical application of its 
processes for the production of the article required, and ascertaining by that 
means how such a method answered, whether it yielded a good product, etc., 
or otherwise, as we have had exemplified in the various criticisms on perchlo- 
ride of iron, nitrite of soda, etc.; but again, on the other hand, we find some 
points, especially those connected with the formulae adopted, where a few con¬ 
cise experiments are all that are required to set the matter, where the doubt 
exists, at once at rest; as was the case with the experiments concerning the 
“ hydration of sulphuric acid,” the “ water of crystallization in granulated 
sulphate of iron,” etc., and also, as in the present instance, is the case with 
the “phosphate of ammonia.” 
Medicinally, phosphate of ammonia is a salt of but little importance, and 
administered probably more for the sake of its phosphoric acid than for that of 
the ammonia ; still the composition assigned to it by the Pharmacopoeia was 
doubtful, and although an unimportant salt, that is no reason why it should 
have an incorrect formula. It was therefore to ascertain the true composition of 
this salt, more especially its proportion of ammonia, when made according to the 
directions of the British Pharmacopoeia, that the present series of experiments 
were made and noticed. I would first mention its preparation, as officinally given, 
which is the following:—20 oz. of dilute phosphoric acid are taken of sp. 
gr. 1-08, and 8 oz. of strong liquid ammonia added; the crystalline precipitate 
which forms, is ordered to be redissolved with a gentle heat, and the solution 
set aside to crystallize; the crystals to be rapidly dried without heat, and en¬ 
closed in a stoppered bottle. As regards the criticism of its preparation,—here¬ 
after ; at present its composition, when this particular method is employed as 
its source, is the question at issue. By referring to the Pharmacopoeia, we find 
it there stated to consist of 3 KII 4 0, P0 5 + 5 HO. Now generally speaking, 
when neutralizing phosphoric acid with an alkali, we do not get a salt contain¬ 
ing 3 atoms of base, but one consisting of 2 atoms of base, 1 of basic water, and 
1 of acid, and in the present instance its composition is still more doubtful, in¬ 
asmuch as authentic works state that the triammoniac salt, even should it be 
formed, cannot be dried and preserved so as to retain the same composition. 
My own experience bears out this latter fact, within certain limits, for I found 
that even in preparing the salt for analysis, using merely ordinary precautions, 
ammonia was so rapidly given off that the estimated NII 4 0 was therefore 
somewhat too low, and consequently the P 0 5 rather too high, giving to the 
analysis rather an unscientific appearance ; still, I am happy to say that the 
results show that for once the formula given by the Pharmacopoeia is correct. 
Of salt so prepared,— 
•393 gramme gave 38-06 percent, of PO r> . 
•407 „ „ 38-02 
These were estimated by a volumetric solution of nitrate of uranium ; and 
again, -532 gramme gave 37-89 per cent. P0 5 , estimated as pyrophosphate of 
magnesia. By combustion with soda-lime by Varentrapp’s process,— 
•255 gramme gave 39-05 percent. NII 4 0. 
•410 
38-2 
jj 
2 o 
VOL. VI. 
11 
