PRESERVATION OF SYRUP OF IODIDE OF IRON. 
423 
An experiment will at once prove my hypothesis correct. To a solution of 
any iodide add a little persalt of iron,—an immediate evolution of free iodine 
will be the result according to the following equation :— 
FeI + Fe 2 Cl 3 = 3FeCl + I. 
That the iodine is “free” is proved by the readiness with which it is re¬ 
moved from solution when shaken with ether,—an observation first made by 
Dr. Squire, I believe. 
If, however, previous to the addition of the iron salt a little phosphoric acid 
be added, no coloration takes place until the whole of such acid has first been 
removed in the form of perpliosphate of iron. In order for this latter experi¬ 
ment to succeed perfectly, the iron should be combined with an acid that in the 
free state has not the power of dissolving perpliosphate of iron,—with acetic acid, 
for instance. The presence of a minute quantity of hydrochloric acid would 
tend to keep the perphosphate in solution, and coloration more or less would 
consequently ensue. 
According to this view, phosphoric acid is the only acid that can be relied on 
for the preservation of syrup of iodide of iron, and my first impression as to the 
utility of sulphuric acid could only have been true in a very limited sense. In 
the long-run, it could not have been otherwise than harmful. 
Professor Redwood, having been appealed to by the President, regretted 
that the effects of a severe cold prevented his offering more than a very few re¬ 
marks on this paper, but he was by no means prepared to admit that there was 
any occasion for making the addition suggested. Syrup of iodide of iron, if 
well prepared according to the Pharmacopoeia and carefully kept, would remain 
good for a considerable length of time. 
Mr. Ince saw no reason for adding the phosphoric acid, and therefore en¬ 
tirely disapproved of it. He did not see why any addition should be made to 
the pharmacopoeia process, which seemed to answer very well, and which he 
adopted long before the issue of the present edition. It was a simple‘and easy 
process, and the syrup might be made almost while the customer was waiting 
for it. 
Mr. Gale had adopted the plan of the present pharmacopoeia for the last ten 
years and found no difficulty whatever. He used rather less water than was 
indicated, and was always successful. His preparation would keep about six 
months. 
Mr. Ince said he always deducted a quantity of water, which was accounted 
for in the solution. 
Mr. Gale always used the same quantity of water as of iodine. 
Mr. Wood could not quite go with all that had been said, as he had seen cases 
where the syrup had changed colour, but they were certainly cases in which a 
severe test had been applied. A quantity of the syrup having been put away 
in a bottle half full, in about three months there was a distinct layer of colour 
on the surface, which was proceeding downwards, but of course, having been 
put away improperly, the test was an unfair one. Still, it must be admitted 
that the syrup would undergo discoloration if much exposed to the air. He 
begged to suggest that Mr. Grove had not made his experiments completely, as 
he had not tried the addition of a little hydriodic acid, which he thought 
would tend to preserve the syrup from discoloration, and perhaps the addition 
of sulphuric or phosphoric acid would tend to the elimination of a little hy¬ 
driodic acid, and that might explain its action. The addition of hydriodic acid, 
however, would be as convenient, and more in accordance with the character of 
the preparation. It was hardly, however, worth the trouble of investigating, as 
the ordinary process answered every practical purpose. 
