July L, L91S 



THE INDIA RUBBER WORLD 



537 



Prai l CAL I ONSIDERATIONS. There is considerable evidence to 

 warrant the assumption that the "insoluble" matter in crude rub- 

 be! has in important bearing on vulcanizing capacity, but no 

 quantitative relation has been discovered. While it has been 

 shown that the removal of the "insoluble" markedly decreases 

 curing capacity, the experience of the author is that rubbers with 

 low proportions of "insoluble" do not necessarily cure badly, not 

 do samples with high "insoluble" necessarily cure rapidly. Prob- 

 aUv "insoluble" varies su in composition that further methods of 

 separation must be devised before "insoluble" can be taken as a 

 criterion of quality The author prefers the indirect method 

 for determining "insoluble," which consists in evaporating a con- 

 venient volume of clear solution, obtained by treating 0.5 to 1 

 gram of rubber with 100 to 200 c.c. benzene in a tall cylinder, 

 allowing to settle and weighing the residue in a pipetted portion 

 drawn off from above the residue. 



Estimation of Rubber. Assuming a satisfactory method of 

 separating the "insoluble" matter, the mosl satisfactory indirect 

 method of estimating rubber is by deducting the sum of moisture 

 plus resin plus "insoluble" from 100. This method involves the 

 assumption that the whole of the ash and nitrogen are present in 

 insoluble form I be author recommends the return of the 

 analysis in the following form: 



Moisture Per cent. 



Resin (acetone extract ) 



Insoluble matter 



Rubber i difference) 



The above contains : 



Ash (mineral matter) 



Nitrogen 



Nitrogen = protein 



These notes apply only to routine technical analysis of which 

 the chief object is to ascertain whether a distinct abnormality is 

 disclosed and to control methods of production or of gauging 

 suitability for specific manufacturing purposes. 



Direct Method by Tetrabromide for Determining Rubber. 

 The reader is referred for details of this method to the work by 

 Caspari on "Laboratory Methods for Rubber Analysis." 



The reaction of bromine on caoutchouc is G<, H,« -f- 6 Br = 

 C,„ ll„ Br, + 2HBr. 



Estimation of Moisture. The best method is (1) to dry in 

 water oven at 98 degs. C. till an increase in weight becomes ap- 

 parent or for a standard time of 2 hours, or (2) to take the 

 difference between original weight of sample and weight after 

 acetone extract plus the extract. 



\\ \shing Loss. It is generally agreed that if the sample is 

 large and requires washing the analytical determination should 

 b i .irried out on the washed, air-dried material. 



Physical and Mechanical Tests. 



\ COSITY. \ low viscosity almost invariably indicates poor 

 quality. A determination of swelling capacity (per Caspari) 

 may give more satisfactory results. 



Vdhestve Test. Beadle and Stevens determine the load re- 

 quired to separate pieces of paper evenly coated with a solution 

 of rubber. The paper is coated by drawing it over the surface 

 of a 5 per cent, (or less) solution. 



Mechanical Tests. By this is meant tensile tests. These are 

 of no value as applied to raw rubber. 



Vulcanization Tests, (a) Material. — State of aggregation 

 (degree of polymerization) or physical condition of the rubber 

 substance, quality and nature of resin, and of "insoluble" matter 

 and acidity, 



(b) Process. — Temperature, duration of cure, method of heat- 

 ing, quantity of sulphur; and if fillers are used, their nature and 

 quantity. So long as our knowledge of the physical and chemical 

 nature of the impurities and of the rubber substance is incom- 

 plete it is impossible to devise any method of analysis or physical 

 test which will en tble us to determine quantitatively the effect of 



the various factors on vulcanization. Direct vulcanization tests 

 are therefore, for the present, essential for the purpose of prac- 

 tical e 



Broadly stated such may comprise: (a) Observations on mate- 

 rial during or rather towards the process. 



(b) Observations n the nature of the vulcanized product with 

 regard to "rate of cure." relying on the mechanical properties of 

 the cured stock. 



There appears to be no direct connection between the 

 efficient of vulcanization" and the technical properties of the 

 material. Various types f tensile tests have been devised and 

 are applied to vulcani/ed rubber. There is an essential differ- 

 ence between tests for the comparative evaluation of crude rub- 

 ber and tests appbed with tlte view of examining the specific 

 properties of any given rubber article. With ■ the former 



it is desirable to use methods calculated to measure certain in- 

 trinsic and typical properties of the raw material, such as curing 

 capacity, strength, distensibility and capacity for recovering. 



Any system of evaluation based on factors influencing the vul- 

 canization process must lie carried out under standardized con- 

 ditions of mixture, cure and test. Pure rubber and sulphur are 

 considered the best because most uniform and also because a 

 Idler renders the reaction less delicate. 



II. Vulcanized Rubber. 



Preparation i or Analysis. This is accomplished by grinding 

 the sample to a fine powder by a pair of steel or iron rolls. 



General Scheme of Analysis. A preliminary qualitative test 

 is made with cold benzene or nitro-benzene. If the solvent does 

 not become appreciably colored (yellow or brown) or fluorescent 

 no considerable amount of bitumen has been used. Such mate- 

 rials vulcanize to a certain extent and may become more or less 

 insoluble in consequence. If qualitative tests give positive re- 

 sults the method of analysis must be selected. For the separa- 

 tion of minerals, starch, fibers, etc.. high boiling point petroleum 

 should be employed as a solvent. 



PATENTED TREATMENT OF RUBBER. 



Elastic and Plastic Substitute i ir Rubber. J. Stockhausen, 

 German patent No. 280,144, elastic and plastic masses are ob- 

 tained from glycerol-gelatin solutions by the addition of arti- 

 ficial resins from phenol and HCHOH glycerol-gelatine, es- 

 pecially the camphor-glycerol-gelatine masses obtained according 

 to German patent, No. 277.653. The products are applicable 

 in the manufacture of water hose. For example, gelatin, 2.5 

 kilos, is dissolved in glycerol, 2.5 kilos, and then intimately mixed 

 with 0.5 to 1 kilo of camphor in acetone. 2 to 4 kilos shredded 

 asbestos, 0.3 to 1 kilo sulphur, 0.5 kilo Frankfurter black, and 1 

 to 1.5 kilos phenol-resin; whereupon the mass is hardened and 

 worked further according to the known methods. [Presumably 

 this would be mastication on ordinary rubber warming mill, in 

 preparation for feeding to a tubing machine for formation of hose 

 tubes, etc.] 



Sponge Rubber. Philip Schidrowitz and I Idborough, 



British patent. No. 1.111 (1914). This is an interesting new de- 

 parture in the manufacture of sponge rubber. The usual processes 

 for producing foamy or cellular rubber are has. I ub ' intially 

 on the principle of adding to the ordinary plastic rubber mixing, 

 volatile or gas-forming substances, which, on the application of 

 heat, give rise to a porous or cellular formation in the mass by 

 their effort to escape. 



The improved process of making rubber sponge is simple and 

 economical, being carried out directly on the rubber latex. The 

 method consists in first coagulating the latex under conditions 

 producing a porous or spongy coagulum and then fixing the cel- 

 lular structure so produced by vulcanization in a wet state. The 

 amount and nature of the coagulant used depends on the nature 

 and condition of the latex and character of product desired. 



In the case of Hevea latex, acetic acid, other suitable acid or 



