578 
PHARMACEUTICAL MEETING. 
because, although both works indicate the same specific gravity (l-04),*he finds 
by calculation that the acid of the B.P. 1864 contained only 8 - 3 per cent., 
while the B.P. 1867 specifies that the acid contains 9-2 per cent, of S0 2 . Now 
the B.P. 1864 only indicated that 164 measures of iodine solution should be re¬ 
quired for the oxidation of a fluid drachm of the acid, and it is from these data 
that Mr. Umney calculates the 8-3 per cent, of S0 2 . But after carefully re¬ 
peating the calculations, I confess I cannot arrive at Mr. Umney’s result, and 
am led to believe that my original statement is perfectly accurate. A fluid 
drachm of water weighing 54-68 grains, a fluid drachm of acid of sp. gr. 1-04 
will weigh 56-87 grains. 164 measures of iodine solution will oxidize 5*248 
grains of S0 2 . Consequently, if 56 87 grains contain 5'248, then 100 will 
contain 9’2 and not 8\3. 
I do not know whether I am justified in speculating as to the source of this 
discrepancy in the results of a simple calculation, but, if I may be permitted to 
do so, I would suggest that Mr. Umney has followed the common but erroneous 
assumption, that a fluid drachm of water contains 60 grains. This would 
exactly account for the difference in our results. Of course the real weight of 
a fluid drachm of water is 54-68 grains, and is so given in the Pharmacopoeias. 
The experimental results which Mr. Umney has given us in this paper are of 
very great interest and value, especially at the present time, when sulphurous 
acid is being frequently ordered for administration and for use in the form of 
spray. As far as I gather, Mr. Umney finds it very difficult or almost impos¬ 
sible to prepare a solution of sulphurous acid of the strength given in the 
Pharmacopoeia, unless pressure be employed to augment the solubility. I con¬ 
fess I have never met with this difficulty, providing a copious and sufficient 
stream of gas be employed, conducting the operation out-of-doors, or somewhere 
where the fumes can be carried away. I prepared in three hours this morning 
a pint of the acid having a sp. gr. 1-048, by simply bubbling a rapid stream of 
gas through the water, keeping both the wash-bottle and the receiving-vessel 
cool; but I entirely agree with Mr. Umney that it would be impossible to do 
this with the exact proportions of ingredients ordered in the Pharmacopoeia. 
Unless the quantity of charcoal and oil of vitriol be much augmented in relation 
to the water to be charged, it is impossible to make a saturated solution. I may 
add, as a little practical point which may be of use to some, that an ordinary 
iron quicksilver-bottle forms a convenient flask for generating the gas. These 
bottles are to be found in most laboratories, and they are of little or no use. 
It is simply necessary to remove the screw-plug and fit in a cork, with the bent 
tube leading to the wash-bottle. The flame of a large Bunsen burner may be 
applied direct to the iron vessel without any fear of breakage, and a rapid 
stream of gas at once obtained. The action of strong oil of vitriol, when hot , 
upon iron is quite different to that of dilute sulphuric acid ; no hydrogen is 
liberated, sulphurous acid being formed by a chemical change analogous to that 
which occurs in the case of copper. 
There is one other point in connection with the Pharmacopoeia description of 
sulphurous acid, which Mr. Umney did not refer to in his paper, but which appears 
to me to be of considerable importance in experiments determining the exact 
strength of acids of different gravities. I refer to the test given for determining 
the percentage of S0 2 by a standard solution of iodine. The reaction between 
iodine and sulphurous acid was made the basis of a general method of volumetric 
analysis a long time ago, and has been carefully studied by chemists. All those 
who have worked with it are aware that it is liable to furnish erroneous and dis¬ 
cordant results unless certain precautions are taken. Bunsen, who subjected 
the method to a most searching investigation, has indicated that to ensure accu¬ 
racy, the sulphurous acid operated with must be previously diluted until its 
strength does not exceed 0-04 per cent. Now the Pharmacopoeia directs 34-7 
