ON SYRUP OF PHOSPHATE OF IRON. 
139 
It seems then that the oxide deposited by the syrup corresponded closely with 
No. 2, the analogue of octocalcic phosphate. 
The colour of the syrup was found to be readily discharged by addition of 
permanganate of potash, a fact of course of no practical value, but suggestive of 
the cause of coloration. After being thus treated, it deposited rapidly per- 
phosphate, the syrup at the same time regaining its dark colour. 
Shaken with purified animal charcoal it was almost completely decolorized, 
the amount of oxidation, as indicated by deposition of perphosphate, being 
small. This simple process might, I think, be legitimately employed to restore 
a coloured syrup of phosphate of iron to saleable condition, subject of course 
to certain limitations. 
In preparing syrup of phosphate of iron I deviate somewhat from the B.P. 
instructions. The precipitate obtained by the use of cold solutions is so tedious 
to wash that I venture to use half the quantity of boiling water, and maintain 
the boiling till the hydrate is decomposed and the precipitate becomes sandy. 
It may then be washed by decantation first, finally on a filter with great ra¬ 
pidity and little exposure to oxidation. There is however a loss of phosphate, 
the yield being 80 grs. only instead of 96 grs. This I allow for by using one- 
fifth more of ingredients. The phosphoric acid I use is prepared from amor¬ 
phous phosphorus, and is four times the strength of the acid of the Pharmaco¬ 
poeia. By careful treatment the solution of phosphate for one Pharmacopoeia 
quantity may be got into the volume of 4 oz., so that it is then only necessary 
to add 8 oz. of syrup to complete the article. Of a syrup so prepared, several 
1 oz. quantities were (Dec. 11, 1867) set aside in 2 oz. corked phials, exposed 
to diff used light in my laboratory. 
No. 1 = the pure syrup, ferri phosph., B.P. 
No. 2 = do. -f 4 grs. pot. chlor. 
No. 3 — do. -f- 4 grs. pot. nit. 
No. 4 = syrup half the strength as regards sugar as syrupus, B.P., not dif¬ 
fering in other respects from No. 1. 
No. 5 = syrupus -f acid. ph. dil. 
No. 6 = syr. ferri phosph. + 4 grs. sodje hypophosph. 
Feb. 8, 1868. Nos. 2 (which had deposited nearly the whole of its phosphate 
immediately on the addition of the chlorate), 4, and 5, were practically colour¬ 
less. Nos. 1, 6, and 3, were coloured, the last less so than the other two. It 
was also distinguished by a deposit of pinkish-white perphosphate. 
Aug. 12, 1869. No. 1 (the pure syrup) was much the darkest of the series, 
and had deposited a little perphosphate. 
No. 3 (containing nitrate of potash) was about half as dark in tint, but had 
deposited more perphosphate. 
No. 6 (containing hypophosphite of soda) was of about the same as No. 3, 
but had deposited less perphosphate. 
No. 4 (containing only half as much sugar as syrupus, B.P.) was much paler 
than either of the others,—in fact usable. 
No. 5 (syrup of phosphoric acid) had acquired a pale straw tint. 
No. 1, treated on the 12th inst. with animal charcoal, lost the greater portion 
of its colour. 
The conclusion I derive from these experiments, as to the cause of the colo¬ 
ration, is this,—that it is mainly due to the formation of caramel, under the 
joint influence of phosphoric acid and of proto-phosphate of iron undergoing 
oxidation on a dense syrup. In order to check this process, I recommend the 
use of less sugar, and to facilitate the preparation of the phosphate, the use of 
boiling water, etc., in the manner I have already indicated. 
