422 
PHARMACEUTICAL MEETING. 
Query, then would either or both of these acids when added to syrup of iodide 
of iron tend to its preservation, i. e. to prevent its acquiring colour when ex- 
posed freely to the air ? 
I was the more readily inclined to answer this question in the affirmative 
from a belief that I had somewhere seen recommended for the same purpose 
the use of citric acid. (After a long search I have failed to ferret out the 
paper in which the observation occurred, and am therefore unable to credit 
the author of the suggestion with the “kudos” due to him.) 
I may observe that a strong solution of iodide of iron, prepared with pure 
iodine and iron in the form of fine wire, invariably reddens litmus paper. 
Whether it is due to impurities in the iron, or is characteristic of neutrally 
constituted iodide of iron, not having by me an absolutely pure specimen of 
iron, I cannot say. 
My experiments were conducted by making seven specimens of syrup—from 
iron wire, best iron tacks, common iron tacks, wire + acid, sulph. dil. in. j per 
oz., ditto -f- acid, phosph. dil. m ij per oz., ditto + acid, phosph. dil. in ij and 
acid, sulph. dil. in j per oz., ditto + acid, phosph. dil. in viij per oz. 
These were placed in partially filled bottles and exposed for some months 
to diffuse daylight. It was soon apparent that the acidulated syrups had a 
decided advantage over those not acidulated. The syrup made from best tacks 
was superior to that made from wire; that made from common tacks was 
inferior to either ; the nature of the acid appeared to be immaterial. 
Since then I have settled down to the use of dilute phosphoric acid, of which 
I add half a fluid ounce to each pharmacopoeia quantity (31 fl. oz.). With 
that proportion I find the syrup keep perfectly well for any length of time, 
and without the slightest reference to the bottle containing it being full or 
only partially full. If I remember right a less proportion does not answer quite 
so well, and would not meet the case of a country dispenser with irregular calls 
for the syrup. Purists will, of course, object to this tampering with the Phar¬ 
macopoeia, so should I perhaps, but I do it permissu superiorum. Besides which 
I may truly say that I have never in the course of dispensing found any reason 
to regret the presence of the interpolated ingredient. 
Before adopting this expedient I used to seal up my stock in six-ounce bottles, 
.which I completely filled with the hot syrup and then tied over with strong 
and well-soaked bladder-skin. This, after several trials, I found the best mode 
of excluding the atmosphere. 
It is obviously necessary to observe one precaution,—don’t add the acid to the 
syrup before it has completely cooled. Not observing this, I on one occasion 
found a batch of syrup go utterly wrong from the formation and crystallization 
of glucose, which, singularly enough, did not make its appearance until the bottles 
of syrup had been uncorked for a day or two. 
I was quite at a loss to explain the modus opercindi of the phosphoric acid, 
until it occurred to me to ascertain how the syrup so additioned would bear 
dilution with water, and how keep when so diluted. Mere dilution did not 
affect its transparency when the proportion of water to syrup was as seven to 
one even, but on exposing the mixture in an open vessel to the air, I observed 
the fluid to gradually deposit a white sediment of perphosphate of iron, until 
about half the water had spontaneously evaporated ; then, and not till then, did 
it begin to assume the tint of oxidizing iodide of iron. 
The coincidence of the disappearance of the phosphoric acid, and the evolution 
of free iodine, seemed to prove the preservative effect of the acid to be due to 
the fact that the iron as soon as it arrives at the state of peroxidation is at once 
seized by the phosphoric acid, and the compound thus formed being insoluble in 
any of the fluids present, the reduction of the hydriodic acid by the peroxide is 
prevented. We have, of course, still the free hydriodic acid, but in the presence 
of syrup it is oxidized very slowly, in fact, almost imperceptibly. 
