218 
BRITISH PHARMACEUTICAL CONFERENCE. 
quite agree with those previous writers who are of opinion that a 5 per cent, 
solution of sulphurous acid is of ample strength for all ordinary purposes; 
but, at the same time, I cannot admit the existence of any insurmountable 
difficulties in the way of preparing it of 1| times or even twice the above 
strength. 
The following table shows the mean specific gravities at 60° F. of pure 
solutions of sulphurous acid, containing from 0‘5 per cent, up to 10 per cent, 
of the anhydrous acid. I believe their accuracy may be depended upon, the 
determinations having been made by oxidation and conversion into the 
barium salt of sulphuric acid:—• 
Per Cent, of 
SO 2 . 
Sp. Gr. at 
60°. 
Per Cent, of 
SO 2. 
Sp. Gr. at 
60°. 
Per Cent, of 
so 2 . 
Sp. Gr. at 
60°. 
0-5 
1-0028 
4-0 
1-0221 
7-5 
1-0401 
1-0 
1-0056 
4-5 
1-0248 
80 
1-0426 
1-5 
1-0085 
5-0 
1-0275 
8-5 
1-0450 
2-0 
1-0113 
5-5 
1-0302 
9-0 
1-0474 
2-5 
1-0141 
6-0 
1-0328 
9-5 
1-0497 
8-0 
1-0168 
6-5 
1-0353 
10-0 
10520 
3-5 
1-0194 
7-0 
1-0377 
I have hastily examined eight specimens of “ sulphurous acid B. P.” pur¬ 
chased of various retailers; I give the specific gravities and percentages of 
S0 2 of each, the differences between these and the corresponding figures in 
previous table being due to sulphuric acid:— 
No. of 
Sample. 
Sp. Gr. at 
G0°. 
Per Cent, of 
S02. 
No. of 
Sample. 
Sp. Gr. at 
60°. 
Per Cent, of 
S02. 
1 
1-022 
3-4 
5 
1-042 
7'8 
2 
1-017 
2-7 
6 
1-031 
4-9 
3 
1-019 
2-4 
7+ 
1-016 
2-5 
4# 
1-032 
6-1 
8 
1-024 
3-7 
Several substances appear to exercise & preservative action upon sulphurous 
acid, or in other words retard its oxidation, among them grape-sugar, formic 
acid, camphor, and more especially aldehyde; and I think it might be worth 
while to ascertain, firstly, the exact amount of influence exerted by the last 
two, and secondly, whether the addition of either, in small quantities, would 
present any very serious objections. 
Sulphuric acid is naturally a very unwelcome ingredient; but old sul¬ 
phurous acid containing it may be restored for all practical purposes by the 
cautious addition of a solution of sulphite of barium in sufficient quantity 
to precipitate very nearly, but not quite all the sulphuric acid as insoluble 
sulphate of barium, the latter being afterwards separated by filtration or 
decantation. I lay perhaps rather more stress upon the use of sulphite of 
barium than I should have done if I had not seen the extremely pernicious 
effects of some of the acid ordinarily sold, when used in the form of “ spray ” 
for throat affections, owing merely to the presence of an undue proportion 
of the higher oxide of sulphur. 
* Made from impure water. 
f Either very old or improperly prepared. 
