Tinctura Ferri Perchloridi

This tincture and its equivalent, liquor ferri perchloridi, give some curious results now and then owing to interaction of the ferric chloride with other substances. Phosphoric acid is one thing that upsets the unwary dispenser. The following show what may happen:

The first of these, compounded in the order of the ingredients, is inky owing to the tannin of the digitalis combining with the iron; but if the tr. ferri mur. and acid, phosph. dil. are mixed together, diluted with half the water, then the syrup and tincture added, there is no inky tinge about the product. Ferric phosphate is precipitated in No. II., and cannot be avoided owing to the interaction of liq. ammon. acet. with phosphoric acid and liberation of acetic acid, in which ferric phosphate is insoluble. Liq. ammon. acet. may as well be left out, seeing that the diaphoretic effect of ammonium acetate is lost. A precipitate of ferric phosphate is in some other cases unavoidable, as in the following, but the density of the precipitate varies with the way of mixing:

If in No. III. the tincture of iron perchloride and acid be mixed together, and then diluted, a heavy precipitate will fall at once, increasing in density until about the third day, when the maximum is reached. Dilution of the tincture and acid separately before mixing causes the precipitate to fall slowly and in a very finely divided, almost gelatinous, condition. In No. IV. the magnesium sulphate promotes precipitation of ferric phosphate, but if the phosphoric acid is added last, the separation is retarded.

Tinct. ferri perchloridi and all other ferric salts (except the scaled citrates) reduce potassium iodide on mixing solutions, free iodine being precipitated as a black sediment if the potassium iodide is not present in sufficient quantity to keep it in solution. The following equation explains the reaction:

Fe2Cl6 + 2KI = 2FeCl2 + 2KCI + I2

Potassium citrate prevents the liberation of iodine; thus mixture V. is loaded with iodine, and mixture VI. is a yellowish-green solution, destitute of free iodine and remaining so for months:

Mr. Wm. Duncan considers that potassium ferricitrate (K2FeO,C6H5O7) is formed in the latter case. Alkaline citrates thus have the effect of keeping iron solutions together, as it were. Here is another instance:

Any other way of mixing these gives a different result.

A similar reaction occurs with bromides, but not always, as the following show:

Bromine was detected in No. I. by the dispenser, but although No. II. becomes of a deep red colour, Mr. Harold Wyatt found that this was not due to free bromine, but to ferric bromide.

Mucilage of acacia is incompatible with tincture of per-chloride of iron, a slimy ferric arabate being precipitated; but in some cases it is possible to dispense a clear mixture. The following instance is almost historic through frequent reference to it by the late Joseph Ince:

Mr. Ince said that, made most ways, this combination assumes the form of a thick jelly, which may be sent out in a covered pot. Reason thus: Here are three ingredients likely to react upon each other, of which mucilage is chief. There are 10 drachms of protective agent (syrup) at disposal; divide it into 3ij. with the tincture, 3iij. with the spirit of nitrous ether, 3 v. with mucilage, which wants it most. Combine the three solutions, and a beautiful preparation is the result.

Occasionally we have seen tr. ferri perchlor. and spt. ammon. aromat. prescribed together, generally in about equal proportions. They are clearly incompatible, but the mixture is a most useful haematinic, being much less styptic than tr. ferri perchlor. alone, and that appeared to be known to the prescriber who, in the old days of spt. ammon. co., P.L. (a preparation of most uncertain alkalinity), wrote this prescription:

On mixing, effervescence (C02) took place, with some precipitation, which quickly resolved itself, and a nice reddish solution resulted.