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BRITISH PHARMACEUTICAL CONFERENCE. 
turned blue, and so remained till a considerable excess of alkali bad been 
added, no sharp line of demarcation being anywhere visible. 
I have examined most of the specimens for free nitric acid, finding however 
only traces in any of them, also for phosphorous acid, which was absent from 
all I tried, as were also meta- and pyrophosphoric acids. In Ho. 28 I noticed 
a wide difference between the specific gravity and the percentage of acid. 
The acidimetric estimation also showed the presence of considerably more 
acid than the uranium accounted for as phosphoric. I therefore examined 
it further, and found a considerable quantity of sulphuric acid. I then exa¬ 
mined some of the others, but did not meet with it again. 
I have said that the samples made with glacial phosphoric acid contain 
ammonia; this I believe to be so universally the case, that the presence or 
absence of ammonia shows the method of manufacture. The glacial acid is 
made commercially by heating phosphate of ammonia, when theoretically the 
ammonia should be all volatilized; practically however it is not so. The 
amount retained will probably vary with nearly every sample; I therefore 
examined only one, to get some idea of what might be the case. It was 
a sample of German, procured for me by Mr. [Reynolds, and which I found to 
contain 5‘5 per cent, of ammonia; if we consider this to have been present 
as tribasic phosphate, it is equal to 16'7 per cent.; if however it be as mono¬ 
basic or metaphosphate of ammonia, if such a salt exists, there is 44T per 
cent, of it. It is this fact that constitutes the principal objection to the use of 
the glacial acid, at least of the present commercial article, as the source of the 
diluted acid of the Pharmacopoeia. It will be known to many that in the last 
edition of the U. S. P., in addition to a similar process to that in our own, it 
is said that the diluted acid may also be prepared by dissolving ^j Acid. Phosph. 
Glacial, in £iij water, adding forty grains of nitric acid, boiling to syrup, then 
diluting to ^xiiss. Under the head of Phosphoric Acid Glacial in Materia 
Medica, it is however among other tests expressly mentioned that no ammo¬ 
nia is evolved from it when potash is added in excess. 
To the second division of the question, as to the best and safest mode of 
obtaining dilute phosphoric acid of a constant strength, I regret that I have 
been unable to find a satisfactory solution. Under present circumstances, 
I think the 33. P. process—objectionable as it certainly is, more however, as 
I believe, on the score of tediousness than of danger—is the best for use on the 
small scale, and by those comparatively unaccustomed to the manipulation 
of chemical apparatus, both as to the process itself and also as needing no 
explanation of the product beyond making up to a prescribed quantity, after 
of course fulfilling the directions given,—and therefore probably the best for 
insertion in such a work. I am sorry however that I have not had oppor¬ 
tunity of trying further the substitution of amorphous for ordinary phosphorus, 
as suggested by Mr. Groves (Pharm. Journ. vol. xvii. p. 510), as it seems 
likely to be an improvement, and now that red phosphorus is a commercial 
article, might be readily carried out. I had not however seen his suggestion 
till too late for any experimenting on it. If it should be thought worth while 
to continue the question to me, I will endeavour to go further into it during 
the next year. 
Whilst I thus think that of the 33. P. to be the most convenient process, I 
believe that the simple combustion of phosphorus, with proper arrangements 
for supply of air and collection of the acid, will be every way better on the 
large scale. I made my own acid in this way on a small scale with a bell 
glass some years ago, and was able to make eight or ten times the quantity 
in the time as by the pharmacopoeia process. A very good figure of apparatus 
for the purpose is given in Miller’s ‘ Chemistry,’ it may of course be modi¬ 
fied according to circumstances. I have seen somewhere, in some German 
