November 1, 1916. 



THE INDIA RUBBER WORLD 



/6 



What the Rubber Chemists Are Doing. 



VISCOSITY INDEX OF RUBBER. 



THE researches of K. Gorter on the viscosity index as a 

 standard for the preliminary testing of the quality of 

 rubber are abridged as follows, by "Chemical Abstracts" 

 (October 10, 1916). The viscosity index is the logarithim of 

 the viscosity of a 1 per cent solution and is superior as a stand- 

 ard to the viscosity, being less dependent on the temperature 

 than the latter, 1 degree causing a variation in the viscosity 

 index of only O.OOS. Hence it is not necessary in viscosity deter- 

 minations to keep the temperature constant by means of a ther- 

 mostat. The viscosity inde.x multiplied by the factor 70 gives 

 the tensile strength of the rubber sample. Gorter's viscosimeter 

 consists of a pipette with a 10 cm. capillary stem with an 

 opening 1.42 mm. in diameter, the whole fitting into a 150 cc. 

 Erlenmeyer. The indicated capacity of the pipette is 15 cc, and 

 its constant 9.8 at 26 degrees C. One gram of rubber is dis- 

 solved in 120 cc. benzene (not purified from thiophene) with 

 shaking, using a brown flask. The solution is filtered after 24 

 hours and the concentration determined, after which the viscosity 

 is determined by the pipette. The relative viscosity of a rubber 

 solution equals the period of delivery, divided by the constant 

 of the viscosimeter for the solvent used. The viscosity of a 

 rubber solution is dependent on the dimensions of the viscosi- 

 meter used ; hence to obtain comparable results the same instru- 

 ment must invariably be used. 



THF. WEBER TEST FOR SUN CRACKING DEM.XNDS PREC.MJTION. 



D. S. Twiss in the "India Rubber Journal" sounds two im- 

 portant warnings in regard to the use of C. O. Weber's reagent. 



The Weber test depends upon the partial oxidation of strips 

 of rubber with a mixture of acetone and an aqueous solution 

 of hydrogen peroxide. Although this mixture is said to keep 

 unaltered for a long time, nevertheless there is a distinct pos- 

 sibility of its deterioration, \^'hile acetone-peroxide compound 

 is very soluble in acetone and also other organic solvents, such 

 as ether and benzene, it is only sparingly soluble in water, and 

 because of the presence of water in the Weber mixture, crystals 

 of the compound in a practically pure condition may gradually 

 be deposited after a month or so, some of them continuing to 

 float in the liquid. Of course, the separation of such a crystalline 

 compound causes a diminution in the o.xidizing power of the 

 liquid reagent so that tests made with it on various dates may 

 not be accurately comparable. 



Great care should be taken to prevent the accumulation of any 

 considerable quantity of these crystals in empty bottles or else- 

 where, particularly in a dry condition. Despite the seeming 

 harmlessness of the compound thus formed and the fact that 

 it can even be melted at 97 degrees C, it is capable of exploding 

 with frightful violence if subjected to a shock, or if heated above 

 its melting point. One thousandth of an ounce, when heated in 

 an open test tulie. will explode with such force as to shatter 

 the tube, and the explosion of a greater quantity in a large glass 

 bottle would be exceedingly dangerous because of the flying 

 fragments of glass. Obviously the practice of using a freshly 

 prepared reagent not only insures accuracy but personal safety 

 as well. 



THEORY OF COLD VULCANIZATION OF RUBBER. 



The following abstract of the researches of F. W. Hinrichsen 

 and E. Kindscher on cold vulcanization is from the "Journal of 

 the Society of Chemical Industry" (September 15, 1916). 



According to C. O. Weber fin 1894) caoutchouc combines 

 with sulphur chloride to form a series of compounds of which 

 the richest member in sulphur contains 23.62 per cent. Measured 



quantities of a solution of purified Para rubber in dry thiophen- 

 free benzene, were treated with quantities of a solution of sul- 

 phur chloride in benzene in excess of that corresponding to 

 Weber's formula, and the reaction product was purified as 

 described by Weber. In eight experiments the sulphur content 

 found ranged from 15.58 to 28.37 per cent. In another series of 

 experiments, quantities of the rubber solution containing 0.5 

 gram of rubber were treated with quantities of sulphur chloride 

 solution containing from 0.433 to 1.299 grams S: C\-., under con- 

 ditions to exclude the presence of moisture, and after three or 

 four weeks, portions of the solutions were withdrawn and 

 analyzed. The amount of sulphur chloride fixed by the rubber 

 ranged from 0.2526 to 0.2795 grams, corresponding approximately 

 to the formula (Ci„H„)jS2Cl;. The higher results obtained in 

 the first series are attributed to adsorption of sulphur chloride 

 or of sulphur liberated therefrom. The yellowish-white addi- 

 tion compound of caoutchouc and sulphur chloride when boiled 

 with alcoholic sodium hydro.xide solution is converted into a 

 dark brown substance corresponding to the formula, C^jHjoSj. 

 In the technical cold vulcanization process it is considered that 

 adsorption of sulphur chloride by the rubber first takes place, 

 followed by slow chemical comliination and by liberation of sul- 

 phur from the excess of sulphur chloride. Cold-vulcanized rub- 

 lier may thus be regarded as an adsorption product of sulphur 

 in a solid or semi-solid solution of the compound, (C„,H,e)/S-Cl5, 

 in excess of rubber. 



METHODS OF ANALYSIS. 



DETERMINATION OF PARAFFIN IX liLACK SUBSTITUTES. 

 A HUTIN in "Le Caoutchouc & La Gutta-Percha" contributes 

 ** • the following method for the determination of paraffin 

 and waxes in black rubber substitutes : 



Many black substitutes contain paraffin, added intentionally in 

 considerable proportions. Substitutes that contain from 10 to 

 30 per cent of paraffin break with a section showing small white 

 spots, and are friable. If 30 per cent paraffin is present the 

 mass is whitish. Below 10 per cent no such evidence is visible. 



The method of C. W. Weber is used for the analysis of 

 substitutes, modified as follows, for the determination of par- 

 affin. The acetone extract, obtained as usual, is treated with 

 100 cc. of 97 to 98 degree alcohol; the mixture heated by plung- 

 ing the container into boiling water and decanting the liquid 

 on a tared capsule. This operation is repeated 5 or 6 times. 

 Evaporate the liquid and dry residue to constant, and weigh. 



Paraffin, ceresin and other waxes present are thus obtained 

 together. In general, the material is white or pale yellow and 

 composed of impure paraffin. It is necessary to use 98 per cent 

 alcohol, otherwise the paraffin, etc., will not be wholly dissolved. 



RUBBER SUBSTITUTE. 

 "Chemical Abstracts" (October 10, 1916) gives the following 

 account of the method of H. Bayer (German patent No. 288,9()8, 

 June 3, 1914) for the manufacture of an improved substitute 

 for rubber. A rubber substitute is obtained from fatty oils, 

 liquid at the normal temperature, as they are employed in the 

 factice manufacture; by treating the balsam-like substance 

 obtained by dissolving and heating sulphur in oil, with an ener- 

 getic oxidizing substance (preferably dilute nitric acid). The 

 product is soft in the heat, but elastic and tough when cold, and 

 after washing it can be vulcanized with sulphur. The sulphur 

 is at the same time o.xidized, as evidenced by the presence of 

 large amounts of sulphuric acid in the nitric acid. Thi« mass 

 is not completely soluble in any of the known solvents, but it 

 swells up with carbon bisulphide, benzene and many other organic 



