SPILLER ON THE OXIDATION IX.-On the Oxidation of India Rubber. By JOHNSPTLLER, F.C.S. ABOUTfour years ago Dr. A. W. Tlofmann commnnicated to the Chemical Society an. interesting research which treated of the changes that gutta-percha is found to undergo bp free exposure to air under ihe influence of a hot climate and the author brought forward conclusive evidence to show that the deterioration in quality observed in the coating of the Indian telegraph wires was to be accounted for by the gradual oxidation of the natural gum.* From a similar point of view I have lately had an excellent oppor- tnnity of studying the nature of the changes produced in caoutchouc by the operation of like influences. The example to which I beg leave to call attention is one of a very instructive character and indicates a condition which must be observed in the India-rubber mnnufdcture whenever it is desired to ensure the permanence of an unvulcanized material.An article is known in commerce under the name of “Patent Waterproof Felt,” which is manufactured largely for the purposes of a cheap packing and is used in the exportation of silk and other valuable fabrics stationery goods etc. which are liable to be damaqed by water. This material is sold in sheets of great length and usually about a yard wide; it appears to be made by cement-ing or matting together the Fres of cotton wool through the intervention of India-ruhber paste or solution so that after the evaporation of the coal-naphtha or other solvent and passing through rollers a continuous and water-repellent fabric is pro-duced.About six years ago I prirchased some of this so-called waterproof felt and made some useful applications of it in the way of photography; some of the material had however been laid aside until a few weeks since when upon examination it proved to possess no longer the close structure and waterproof qualities of the original article. It then occurred to me to examine once more the material in the same manner that I had tested it six years ago viz. by extrachng the India-rubber with benzol and noting the character of the film left upon the evapo- * Chem. SOC.Qu. J. xiii 87. OF INDIA RUBBER. ration of the solvent. The original fabric thus treated furnished a beautifully white cotton flock and a solution which being evaporated left a highly elastic film of pure India-rubber; but these characters are no longer possessed by the fabric examined at this later period By digesting with benzol the cotton fibres are left; in a discoloured coiidition and a solution is obtained which upon evaporation yields a resiu or brownish yellow brittle substance closely resembling shellac.A considerable quantity of this altered India-rubber has been extracted by solvents and its properties may be thus characterized :-It is freely soluble in alcohol especially if warmed in chloro- form wood-spirit and in benzol as already stated. It is not appreciably soluble in oil of turpentine or bisulphide of carbon and but sparingly so in ether.In alkaline solutions both caustic and carbouated it is freely soluble and niay be again precipitated 011 neutralising with acids. Like India-rubber itself it becomes bleached upon iminersion in aqueous ammonia. The resin fuses below the temperature of boiling water and when more strongly heated in a retort gives off an amber-coloured oil of agreeable aromatic odour besides furnishing water a proof of its containing oxygen. At ordinary temperatures it is extremely brittle and highIy electric so much so that it cannot be powdered in an open mortar without considerable loss. A glass rod coated with the substance exhibits the phenomena of ‘‘resinous electricity’’ when rubbed with silk. The chief examination has been made upon the substance extracted from the fabric by warm alcohol which leaves insoluble besides the cottoil a very small proportion of unchanged India-rubber easily separated by filtration and the amount of the brittle resin extracted in this mariner from a square foot of the fabric weighed after complete evaporation of the solvent over a water-bath 74 grains.A quantitative analysis of this substarlce has been made and the numbers furnished by com- bustion with oxide of copper indicate the following percentages which I have placed in juxtaposition with the figures reported by Dr. Hofmann for one of his compounds :-India rubber. Gutta percha. J. S. A. W. H. Carbon .. . . 64.00 62.79 Hydrogen .. .. 8.4.6 9.29 Oxygen .. .. 27-54 27.92 HOW ON A DENSE BRINE For the reasons adduced by Dr. Hofmann in the case of the altered gutta-percha examined by him I abstain from constructing a formula and merely regard this substance as an oxidation pro- duct formed directly from caoutchouc by the absorption of atmo-spheric oxygen in much the same manner as resins are formed from essential oils and other hydrocarbons.