In a previous article (1) a simple procedure for determining the sol rubber content of Hevea latex and crude rubber was described. This method

No abstract

From the work of Caspar! (1), Feuchter (2), and others it is now well known that a large proportion of the hydrocarbon in unmasticated crude Hevea rubber diffuses into and is therefore soluble in petroleum ether or ethyl ether when the rubber is covered with these solvents and allowed to stand at room temperature. This soluble form of rubber has been termed "sol," and the residue from a prolonged and repeated solvent extraction is known as the gel skeleton, which contains practically all of the protein and ash of the original rubber associated with the tough and gristly rubber hydrocarbon termed "gel." It is apparent that the terms "sol" and "gel" rubber are somewhat indefinite, as they do not refer to definite fractions or to rubber having definite physical or chemical characteristics.From a purely colloidal viewpoint and by definition all rubber soluble by diffusion into a solvent is sol. However, we must recognize the indistinct borderline between difficultly soluble sol and almost insoluble gel.The so-called sol rubber carefully prepared from acetone-extracted crepe by diffusion into petroleum ether forms a clear, colorless, and highly elastic substance upon evaporation of the solvent. It is almost pure hy-drocarbon2, since it contains less than 0.005 per cent nitrogen and 0.01 per cent ash. Its unsaturation, as determined from its iodine value (3), corresponds closely to the theoretical value for (CiíH^=)".Up to the present time studies of sol and gel rubber have been largely qualitative and confined to crude rubber and to highly purified rubber from latex. This paper will describe a definite procedure designed to determine the proportion of sol and gel in crude rubber and in dried latex films by the use of a petroleum ether diffusion process. The influence of oxidation on the transformation of gel to sol has been studied by the use of this method. A search of the literature indicates that this field has not been previously investigated.1 Presented before the Division of Rubber Chemistry at the Ninety-seventh Meeting of the American Chemical Society, held in Baltimore, Maryland, April 3-7, 1939. * Midgley (5) found from 0.02 to 0.04 per cent of combined oxygen in sol rubber.

The nature of the variations in continuous‐filament nylon and their influence on dyeing behaviour are explained. By the use of a special fabric containing yarn differing in physical and chemical properties by known and controlled amounts, the sensitivities to such variations of many dyes for nylon have been assessed. These results appear in the appendix in tabular form, and are intended to help the dyer to select suitable dyes, by indicating their abilities to cover yarn irregularities. New and current dyeing methods are discussed, and suggestions are made for improved uniformity. Laboratory investigations have shown which new methods offer most prospects of success, and also where more detailed investigation will be of value.