THE “PHOSPHATE OF AMMONIA” OF BRITISH PHARMaCOP(EIA. 5lP 
mention of a very few facts will, I think, at once decide in favour of the former. 
In preparing the Pharmacopoeia salt, a very large excess of'ammonia is used to 
neutralize the phosphoric acid, consequently, when the solution is warmed to 
redissolve the precipitated phosphate, a considerable quantity is evolved ; that 
is, to say the least, wasteful, considering that ammonia is rather a valuable 
alkali; and again, when evaporating the liquor down from the first crystalliza¬ 
tion, so much ammonia is lost that one-fourth part more has to be added to bring 
the salt back again to the triammonic state, it having of course passed during 
evaporation to the diammonic. The product also obtained is exceedingly un¬ 
stable. Now this is after all the great point, for what is the use of getting a salt 
containing an extra atom of ammonia, if when we have got it we cannot 
keep it there. A sliop-bottle continually dispensed from would soon contain a 
considerable portion of the disalt, and on the large scale it would be found im¬ 
practicable to dry the salt properly, and bring it into a saleable state, as it re¬ 
quires to be put under a bell-jar on a porous tile for some days,—an imprac¬ 
ticable proceeding when operating on much more than a pound. As an instance 
of the rapidity with which the salt loses ammonia, some crystals exposed to the 
air for two hours had entirely lost the third atom ; and in one of the specimens 
on the table many of the crystals will be seen to have affloresced, from being- 
left for a couple of days under a bell-jar, with a capsule containing sulphuric 
acid. Now the salt containing 2 atoms of NII 4 0 is open to none of these dis¬ 
advantages ; it is perfectly stable, very readily prepared, and no great loss 
occurs in its manufacture. It may be made from bone-ash on the commercial 
scale, by the same process as “ phosphate of soda” is now prepared ; or phar¬ 
maceutically, from phosphoric acid, by neutralizing with ammonia, and evapo¬ 
rating to crystallization, taking care to keep the solution neutral, or faintly 
alkaline. When this latter point is carefully observed the resulting crystals 
have the exact composition, 2 NII 4 0, II0,P0 5 . If the solution be allowed to 
get acid, the result is not'the same ; several analyses showed them to be a 
mixture of di- and monammonic varieties. 
•4665 gramme gave 57*9 per cent, of P0 5 , 
•4565 ,, ,, 5rb4 ,, ,, 
a percentage exactly intermediate between the two mentioned compositions. 
There is little doubt then, I think, but that the diammonic salt is the one 
which will always be used in pharmacy ; and it is rather remarkable that a 
member of the Pharmacopoeia Committee, the only person I can remember 
having prescribed the salt, which he used to do in combination with Potass. 
Bicarb, and Lithise Cit., always directed the phosphate and carbonate to be 
well dried previous to mixing the -whole together, which drying was effected by 
wrapping the*salts loosely, and placing before a fire, or in a warm situation. 
Plow could the triammonic salt exist in such a condition, when even a consider¬ 
able portion of the ammonia of the diammonic was volatilized ? Perhaps the next 
edition of the Pharmacopoeia may correct such incongruity. 
There is only one more subject which I wish slightly to notice, and which 
moreover being so intimately connected with the phosphates, is perhaps not out 
• of place, viz. the arseniates of the same base. Now every word that has been 
mentioned regarding the phosphates is applicable in all its cases to the arse¬ 
niates, of course substituting As0 5 for PO s . The triammonic arseniate is pro¬ 
duced in the same way, has the same composition, and agrees in every respect 
with its corresponding phosphate: the same notice is applicable to the other 
varieties. 
The arseniate of commerce proved from analysis to be a mixture of di- 
and monammonic salts; its solution was faintly acid, and was most probably 
made by crystallizing a solution of arseniate, without seeing that it was slightly 
2 o 2 
