SULPHUROUS ACID. 
579 
grains of the acid to be mixed with an ounce of water previous to the addition 
of the iodine solution ; but to reach the extent of dilution indicated by Bunsen, 
that quantity of acid must be mixed with about a pint of water before proceed¬ 
ing to its saturation. 
Of course, in using so large a quantity of water, care would have to be taken 
that it had been previously well boiled to expel the oxygen, and cooled out of 
contact with air. Consequently, it follows that if the Pharmacopoeia test is to 
be employed as a method of exact estimation, then the directions given are bad 
and require modification ; but if it is merely regarded as a ready means of judg¬ 
ing of the strength of the acid for practical purposes, then the point I have re¬ 
ferred to is a matter of no importance. I hope it will be understood that in thus 
noticing what appears to me may be a defect in the Pharmacopoeia method of 
testing, I do not wish in the slightest degree to question the accuracy of the re¬ 
sults obtained by Mr. Umney. 
With regard to the relative advantages of a concentrated, and a 5 per cent, 
solution of sulphurous acid, I can cordially concur with Mr. Umney in pro¬ 
nouncing it almost impossible to preserve the Pharmacopoeia acid for any great 
length of time without considerable loss of strength ; but at the same time I also 
find it very difficult to keep a 5 per cent, solution without its undergoing a 
sensible amount of change. It appears to me therefore that to devise a 
definite and tolerably permanent solution of sulphurous acid for medical pur¬ 
poses, is a problem which has not yet been satisfactorily solved. *■ 
Dr. Attfield remarked, with reference to one of the points alluded to by 
Mr. Wood, that probably the word ounce in the Pharmacopoeia was a misprint 
for pint. 
Dr. Redwood said he could not admit that this was the case, nor did he con¬ 
sider, for the purpose contemplated in the Pharmacopoeia, that any advantage 
w r ould result from using the larger quantity of water, as the test could not then 
be so readily applied ; and as the acid could not be kept in a perfectly uniform 
state, but was necessarily subject to constant change, a test that could be easily 
and quickly used, and gave good approximate indications, was what was re¬ 
quired. As the result of long and very considerable experience in the manu¬ 
facture and testing of sulphurous acid, having for many years been accustomed 
to conduct the processes almost daily, he could say, that not only was it quite 
possible to obtain the acid of the strength indicated, but also that the test was 
a good and convenient one for the purpose intended. At the same time, he was 
quite ready to admit what he had stated to Mr. Umney some time ago, when 
referred to on the subject, that an acid much weaker than that ordered, would 
probably be equally, if not more, suitable for the uses to which it is applied in 
medicine, than the strong acid now ordered. He had, in fact, stated to 
Mr. Umney, that the reduction of the strength to a five per cent, solution was 
under the consideration of the Pharmacopoeia Committee, but beyond this he 
did not consider it desirable to urge this point ; for while the stronger acid was 
ordered, it was their duty to follow the directions of the Pharmacopoeia as nearly 
as they could. 
Mr. Umney said his statement of the strength of the acid produced by the 
Pharmacopoeia process was founded upon experiments made by following the 
instructions given, and Mr. Wood admitted that the quantity of sulphuric acid 
and charcoal was insufficient to yield a solution of the full strength. 
2 R 2 
