196 



THE INDIA RUBBER WORLD 



IJANLARY 1, 1917. 



A method for obtaining rubber of iniiform color, originally 

 tried in Ceylon, consists in boiling the fresh coagulum, in pieces 

 the size of one's fist, for 10 or 15 minutes in water. The heat 

 destroys the enzyme and the rubber loses the property of black- 

 ening on exposure to the air. While the rubber is pale the boil- 

 ing makes it sticky and more difficult to dry. 



A third method consists in using small amounts of antiseptic 

 substances to arrest the action of the enzyme. Among these, 

 formaldehyde and bisulphite of sodium are commonly used. The 

 percentages required are extremely small. After accomplishing 

 their work they are removed from the rubber by washing in 

 the crepcing machines. 



Bisulphite of soda has no bleaching action on the rubber itself 

 and is not able to destroy coloring material already formed. 

 It simply prevents the action of the ferment. It is an antiseptic 

 and not a bleaching agent. Vulcanization tests show that rubber 

 prepared with an excess of acid is inferior to that prepared 

 with the minimum of acid. The same is true of boiled rubber. 

 Rubber treated with bisulphide loses nothing of its quality and 

 is scarcely distinguishable from untreated rubber. 

 r.I.K.VCHED RUIiKKK. 

 The influence, of hydrosulphites on strongly colored crepes 

 has been studied by .\ndre Dubosc ( Lc Caoutchouc & la Gutta- 

 percha). The rubber was subjected to the action of sulphoxylate 

 aldehyde of sodium, both hot and cold. Decoloration was more 

 rapid under the former condition, especially in the presence of 

 a small quantity of bisulphite of soda. Air dried, the samples 

 do not remain absolutely white, but turn yellowish, although 

 much paler than the initial color. 



Sulphoxylates, and in general all the hydrosulphites, act on 

 the coloring matter of rubber and by hydrogenation transform 

 it into a leucobase. even if the coloration is old. 



The accidental coloration, observed by Stevens and Clayton 

 Beadle in the coagulation of latex, Dubosc concludes, can be 

 more advantageously controlled by a hydrosulphite of sodium 

 aldehyde or a sulphox\'late aldehyde. 



ST.vr.ILITY AND THE OPTIMUM CURE. 

 The views expressed by Dr. H. P. Stevens on the stability 

 of vulcanized rubber and the "optimum" cure (The Indl^ Rubber 

 WoRLP. October. 1916), are discussed adversely by Philip Schid- 

 rovvitz and H. A. Goldsborough in "The India Rubber Journal" 

 (October 28. 1916). They maintain the value and accuracy of 

 their "correct" cure method of crude rulilicr valuation, as ap- 

 plied for technical purposes. With regard to "correct" or 

 "optimum" cure in relation to aging, the authors state that the 

 results of their experiments may be summarized as follows : 

 Standard mixture, 1(X) parts smoked rubber, 8 parts sul[)hur. 

 /. Scries stored over 1$ months. The samples most closely 

 approximating to the "correct" cure showed less variation than 

 the samples which were obviously under or over-cured, taking the 

 "correct" cure tested 24 hours after vulcanizing as standard. ' 



.'. Series stored over <S' iiioiilhs. In tliree cases out of four 

 a distinct improvement in "tensile product" was observed. None 

 of the results indicate over-cure. 



.;. Short period series. Variation in the rest period between 

 mixing and curing showed some, but relatively slight effect. 

 The shorter the rest period, the slower the rate of cure. 



\'ariation in the rest period between curing and testing exer- 

 cises an appreciable effect on results during, approximately, the 

 first 12 hours, but after that the alteration in properties is slow. 

 The results are in keeping with practical experience on these 

 points. 



Investigation of the relation of combined sulphur to "correct" 

 cure indicates that the former stands in no relation to mechanical 

 properties. 



•■CORRECT" VS. "OPTIMUM" CURE. 

 The authors' original paper on the determination of "correct" 

 cure will be found in "The Rubber Industry," 1914. page 214. In 



brief their method is: (1) Vulcanization is physically and 

 mechanically of a definitely progressive character. Its progress 

 can be accurately expressed graphically by a series of stress- 

 strain curves. (2) From the formula corresponding to the 

 curves it is possible to select that curve, in a series, which repre- 

 sents an ideal balance of tensile properties. (3) The cure cor- 

 responding to such a curve is in fact the "perfect" or "correct" 

 cure under given standard conditions of mixing, curing and test- 

 ing. The method is scientific, admits of exact mea.'^urement, and 

 is independent of any serious experimental error. 



Eaton and Grantham's "optimum" cure is that cure which 

 gives the highest figures for the "tensile product" (breaking strain 

 and elongation at break). The method may yield erroneous 

 results, mainly on account of the fact that on both sides of the 

 "correct" cure, but particularly on the over-cured side, there is 

 a region in which the "tensile product" may he equal to or 

 greater than that of the "correct" cure. Since similar results may 

 be obtained for a number of cures by this method, it may be 

 impossible, in practice, to decide as to which cure, over a range 

 perhaps of an hour or more, may actually represent the "opti- 

 mum." The method gives no definite indication of the state of 

 cure and is dependent on the uncertain character of the "break" 

 and "elongation" figures. 



Kri'.llKU IKSTIXi; l.\" J.\\.\. 



The Central Rubber Station for the Netherlands Indies, at 

 Buitenzorg, Java, in charge of Dr. O. de Vries, is equipped for 

 research and testing purposes, especially for the study of rubber 

 preparation methods and testing samples for control and im- 

 provement of work on the estates. The Bulletin of the Station 

 is distributed by application to the director. 



Dr. de Vries in a lecture before the Malang Planters' Asso- 

 ciation, at Malang, discussed the preparation of plantation rubber 

 and the need for research, considering the relative position of 

 the two principal forms, smoked sheet and crepe. Generally, 

 smoked sheet has a quicker rate of cure than crepe. The tensile 

 strength of smoked sheet need not be below that of crepe, and 

 it is often found to be higher, due to not overworking the coagu- 

 lum as in the case of making crepe. Smoked sheet is inferior 

 to crepe in the matter of uniformity, due to the method of prep- 

 aration. Crepe in Java is generally prepared on older estates, 

 with a long experience and well-regulated routine, whereas sheet 

 making is often undertaken on estates just starting manufacture 

 and, in consequence, the product is not so carefully controlled. 

 The preparation of crepe is practically a mechanical process 

 while the preparation of sheet is still often complicated by the 

 large number of small pans and much hand making. There are 

 also irregularities in drying and smoking, so that the method 

 of preparation affords much more chance for variation. There 

 can be no doubt, however, that it is possible to produce sheets 

 of very uniform quality. 



The excessive rise in |)rice of acetic acid has stimulated re- 

 search with other coagulating material. Sulphuric acid has been 

 tried and it has been found that slight variations in the amount 

 used have an appreciable influence on the quality of the rubber, 

 notably on its rate of cure. Sugar as a coagulant, according 

 to some experts, is likely to cause much variation in the rate 

 of cure, owing to bacterial action in the latex, dependent on 

 the weather during tapping. 



EXTR.VCTINC, DEAD HB]'E.4 LEAVES. 



Negative results were obtained by J. C. G. Vriens in the 

 extraction with benzene of the dead leaves which were still on 

 the Hcvca trees before the normal leaf fall. | Chemical Ab- 

 stracts.] 



WHALE OIL AS .\N ACCELERATOR. 



In referring to the siiggested use, by Marill, of whale oil as 

 a vulcanization accelerator, .^ndre Dubosc remarks in "Le Caout- 

 chouc & la Gutta-Percha," tliat tlie crude oil containing sperma- 



