516 
PHARMACEUTICAL MEETING. 
tion of 79| per cent, of mercury, while the latter had been prepared by the old 
process of admixture of solutions of pearlash, sal ammoniac, and corrosive sub¬ 
limate, and contained but 65^ per cent, of mercury. Not one of the six sam¬ 
ples, however, when quantitatively analysed for metal, gave so much as 79-| or 
so little as 65| parts of mercury in one hundred; the richest yielded 78| per 
cent, of mercury, the poorest 72 per cent., the intermediate numbers being, 
roundly, 78, 76^, 75, and 73. At first I thought that the weaker samples had, 
perhaps, been made by pouring solution of ammonia into solution of corrosive 
sublimate, instead of vice versa , as ordered in the British Pharmacopoeia, the 
double chloride of mercuric-ammonium and mercury (NH 2 HgCl,HgCl 2 ) being 
produced, which contains only 76| per cent, of mercury. But on attempting 
to prepare this compound, I found that it began to turn yellow long before all 
the chloride of ammonium (the by-product) had been washed away, and, there¬ 
fore, before the percentage of mercury in the precipitate had reached 70, or, 
perhaps, 65. Now not a trace of yellowness was visible in either of the six sam¬ 
ples examined. The only other explanation of the facts of the case that pre¬ 
sented itself was that the samples had all been rightly made by pouring solution 
of corrosive sublimate into solution of ammonia, but that the resulting precipi¬ 
tate had been insufficiently washed. This proved correct. The poorer samples, 
on washing, readily furnished chloride of ammonium without losing colour, and 
certain artificial mixtures of true “ white precipitate” (chloride of mercuric- 
ammonium, NII 2 HgCl) and chloride of ammonium, containing respectively 73 
and 72 per cent, of mercury, comported themselves in a heated test-tube in 
much the same manner as samples 5 and 6 in the table. Commercial white pre¬ 
cipitate is, then, as a rule, properly prepared, and not intentionally adulterated, 
but is usually somewhat impure, through the presence of more or less chloride of 
ammonium. 
With regard to the degree of purity or percentage of mercury which “ white 
precipitate” (Hydrargyrum Ammoniatum , B. P.) may reasonably be expected to 
possess, I think, with Mr. Borland, that the character of volatility without 
fusion should be insisted on, and that a sentence to that effect should be inserted 
in the paragraphs relating to this chemical in the next edition of the British 
Pharmacopoeia. Further, I am of opinion that while on the one hand this pre¬ 
paration cannot be expected to yield the theoretical proportion of metal, inas¬ 
much as before the last trace of chloride of ammonium is washed away, the pre¬ 
cipitate acquires an undesirable yellow shade of colour, through slight decom¬ 
position,—that, on the other hand, to keep out unofficial varieties of white pre¬ 
cipitate, and to exclude undue proportions of chloride of ammonium, ammo- 
niated mercury should be described in future Pharmacopoeias as containing not 
less than, say, 78 per cent, of mercury. 
SULPHUEOUS ACID. 
BY C. UMNEY, F.C.S. 
The introduction into the British Pharmacopoeia of remedial agents of whose 
therapeutic value comparatively little was previously known, has been the means 
of giving to medical practitioners new material for research ; and has undoubt¬ 
edly resulted in promoting investigations which otherwise would never have 
been attempted. 
The action.of sulphurous acid, a remedy of antiquity now placed in the Phar¬ 
macopoeia, had been much less studied than it apparently deserved, for recently 
most beneficial results have followed its use in affections of the throat, by means 
of the spray producer, as recommended by Dr. Dewar,* whose experiments with 
* Dr. Dewar’s Pamphlet on Sulphurous Acid. 
