The Propaganda for Reform in Proprietary Medicines, Vol. 2 of 2

by Council on Pharmacy and Chemistry

One of these schemes, and one so simple that it seems at first sight to be hardly worth serious consideration, is that of a solution of iodin in liquid petrolatum. Solutions of this kind have frequently been offered to physicians and the laity. The thing of particular interest is the claim made as to the percentage of free iodin. Five per cent. is frequently claimed. Examination of some of these products in the chemical laboratory of the A. M. A.[216] revealed the fact that they did not contain the claimed amount of free iodin. These questions at once arose: Was the low free iodin content due to intentional fraud, the result of carelessness, or of ignorance? Was it impossible to prepare a solution containing 5 per cent., or did the iodin slowly combine with the oil and disappear?

Several years ago the A. M. A. Chemical Laboratory[217] conducted some experiments on the solubility of iodin in liquid petrolatum, which indicated that a saturated solution would contain about 1.4 per cent. These experiments did not show conclusively that no iodin was absorbed by the petrolatum during the process of solution. For this reason, further experiments were conducted with the view of determining both the solubility in and the extent to which iodin is absorbed (disappears as free iodin), if at all, by liquid petrolatums of various kinds. Theoretically such hydrocarbons should not absorb iodin. The results of these experiments are here given.

A sample of iodin was prepared by sublimation from a mixture with potassium iodid. This sample when dried over sulphuric acid assayed 99.98 per cent. of iodin. Portions of this sample were used in all of the subsequent experiments. To prepare solutions of definite concentrations, in all cases expressed as percentage by weight, an accurately weighed quantity of iodin was placed in a glass-stoppered bottle and an accurately weighed quantity of liquid petrolatum added. The mixture was subjected to treatment as indicated in the various experiments and from the weights of iodin and petrolatum used the percentage of iodin was calculated.

The method of assay employed was as follows: A weighed quantity of the iodin solution was transferred to a bottle or flask by means of several small amounts of chloroform, about 50 c.c. in all. To this was added about 25 c.c. of potassium iodid solution. The mixture was then titrated with tenth-normal sodium thiosulphate until on thorough shaking no iodin passed into the aqueous layer.

To 2.1248 gm. of iodin was added 199.3 gm. of liquid petrolatum. The mixture was shaken frequently each day and after forty days there seemed to be still a few particles of iodin undissolved. The supernatant solution was assayed, however, and found to contain 1.038 per cent. of iodin. The iodin added was 1.055 per cent. Six months later 1.025 per cent. of iodin was found.

To 5.1832 gm. of iodin was added 199.5 gm. of liquid petrolatum. The mixture was heated to 100 C. for four hours with frequent shaking. The iodin was in perfect solution. The per cent. of iodin would then be 4.95. Upon cooling, iodin in abundance crystallized out. After standing a few hours, with frequent shaking, the iodin in solution was determined. This was found to be 1.425 per cent.

These two experiments indicate: First, that the previous findings of the A. M. A. Chemical Laboratory are correct in that only about 1.4 per cent. of free iodin is retained in solution in liquid petrolatum at room temperature. Second, that the quantity of iodin absorbed by liquid petrolatum at room temperature, in seven months at least, is practically none. Third, that iodin dissolves rather slowly in liquid petrolatum at room temperature.

In the experiments, the results of which are tabulated below, the iodin and liquid petrolatum were heated at 100 C. for about four hours, shaking frequently to hasten solution. After cooling, the specimens were assayed and were again assayed at intervals as indicated in the table.

Kind of Liquid Petrolatum Used	Date of Manufacture and First Assay	Weight		Per Cent. Iodin Used	Per Cent. Iodin Found	Per Cent. Iodin Nov. 17, 1918	Per Cent. Iodin† Nov. 19, 1919
		Iodin	Petrolatum
Stanolind	10/17/18	2.089	188.4	1.096	1.085	1.068	1.067
Squibb	10/14/18	1.9569	186.78	1.0306	1.0232	1.013	1.009
Unknown, bulk*	10/28/18	1.9497	158.2	1.225	1.133	1.075	1.095
Parke, Davis & Co	10/24/18	2.0869	167.43	1.241	1.2488	1.191	1.180