June 1, 1917.] 



THE INDIA RUBBER WORLD 



517 



What the Rubber Chemists Are Doing. 



NATURAL COAGULATION OF THE LATEX OF HEVEA BRASILIENSIS. 



THE phenomena of natural coagulation of the latex of Hevea 

 BrasilicHsis is under investigation by L. E. Campbell, who 

 presents a preliminary account of his research in the "Journal 

 of the Society of Chemical Industry" (March IS, 1917), condensed 

 as follows : 



Reference is made to the hypothesis of Whitby that four 

 agencies are responsible for the changes that take place in 

 the latex of cultivated Hevea Brasiliensis, namely a coagulating 

 enzyme, an oxidase, anasrobic putrefaction, and aerobic putrefac- 

 tion. The present paper concerns only the coagulating enzyme, 

 the nature of which has been determined to some extent. The 

 natural coagulation of latex bears a superficial resemblance to 

 the clotting of blood. It is known that blood contains a coagu- 

 lating enzyme and that lime salts (calcium chloride) exert a 

 particularly favorable influence on the rapidity with which the 

 clotting of blood takes place. On the other hand, if blood be 

 collected in a solution of alkali oxalate it does not clot, owing 

 to the precipitation of the calcium oxalate. Again, the presence 

 of calcium salts plays some part in the coagulation of milk by 

 rennin. 



Coagulating enzymes are known to occur in certain plants, 

 and some of these are known to require the presence of calcium 

 salts for their action. 



Two sets of e.xperiments were carried out, one on the influ- 

 ence of the addition of calcium chloride and the other on the 

 influence of the addition of precipitants of calcium. 



Latex, when rendered alkaline with the hydroxides of sodium, 

 potassium or barium, did not coagulate at all. It is, therefore, 

 probable that the coagulating enzyme of Hevea late.x requires an 

 acid medium for its action. 



The author states in conclusion as follows : 



The natural clotting of Hevea latex is aided by the addition of 

 calcium chloride. 



So far, salts of other metals have not been found to produce 

 an equal effect. This natural clotting is retarded or inhibited by 

 (1) heating; (2) addition of neutral or faintly acid solutions of 

 precipitants of calcium, namely, potassium oxalate and sodium 

 fluoride; (3) rendering the latex alkaline in reaction; (4) for- 

 malin. 



In the case of formalin, the phenomena are somewhat com- 

 plicated by the fact that by the prolonged action of formalin on 

 latex, a peculiar condition of the latex is produced. It retains 

 its superficial appearance but is in reality a suspension of flakes 

 of coagulated rubber in a clear serum, the Brownian movement 

 of the particles having ceased. The factors concerned in the 

 "natural" coagulation of latex are, like those concerned in the 

 coagulation of blood, somewhat complex. In the latter case it is 

 not yet clear how the coagulation is effected. 



In view of the uncertainty as to the mechanism of the coagula- 

 tion of blood it is not proposed to offer explanations as to the 

 mechanism of the coagulation of latex. From the evidence 

 obtained, however, it is fair to assume that : 



(1) The natural coagulation of latex depends upon the action 

 of an enzyme. 



(2) The action of this enzyme is encouraged by the presence 

 of calcium ions. 



(3 ) The enzyme does not act in an alkaline medium. 



(4) According to Whitby the coagulation can take place in 

 the absence of air. 



It has frequently been stated by various investigators that 

 latex as it emerges from the latex vessels is alkaline in reaction, 

 afterwards becoming acid on exposure to air. It is possible 

 that the coagulating enzyme is enabled to act only on the devel- 

 opment of this acidity. 



In the experiments the addition of a given amount of calcium 

 chloride to a given amount of latex on one day did not produce 

 the same effect as an equal amount of calcium chloride on the 

 same amount of latex on another day. The same applies also' 

 to the action of potassium oxalate and of sodium fluoride. 



This difference is probably due not to the fact that the latices 

 on the two days contained different amounts of enzymes, but 

 ratlier to the fact that the latices had been examined at different 

 times after collection. The action of the enzyme had already' 

 proceeded to a greater extent in one case than in the other. 



It is to be noted that the latex contains a carbohydrate, 

 /-methylinosite. 



Many enzymes appear to be combinations of protein and car- 

 bohydrate, and it is possible that /-methylinosite may prove to be 

 part of the enzyme of Hevea late.x. 



Serum from pure latex contains up to four per cent of solid 

 matter. 



The author is continuing his investigations on coagulation. 



THE NATURAL ACCELERATION OF PARA RUBBER. 



Dr. Henry P. Stevens has investigated the natural accelerator 

 of Para rubber for the Rubber Growers' Association and pre- 

 sents an extended account of his work in the "Journal of the 

 Society of Chemical Industry" (April 16, 1917), of which the 

 following is a condensation : 



In various papers Dr. Stevens has shown that certain con- 

 stituents normally present in raw rubber are necessary for its 

 satisfactory vulcanization. These constituents are (1) the nitro- 

 genous complex or "insoluble" constituent which is almost 

 wholly insoluble in benzene, chloroform, and similar solvents ; 

 ( 2) matters which can be extracted with acetone — mainly resins. 

 Also the insoluble constituent can be replaced by other nitro- 

 genous matter, such as peptone, to a lesser extent by casein, 

 and to a sli.ght extent by non-nitrogenous substances, such as 

 starch. The acetone-soluble constituents (mostly natural resin- 

 ous matter) have not been satisfactorily replaced by other resins, 

 such as colophony. From this it may be inferred that the active 

 constituent contained in the acetone extract consists of matter 

 other than resin, although the latter bulks largely. The removal 

 of the nitrogenous matter has the effect of retarding vulcaniza- 

 tion, but does not affect the stability of the caoutchouc or the 

 vulcanized rubber. The removal of the acetone-soluble matters 

 not only tends to retard vulcanization, particularly when the 

 rubber is compounded with litharge, but also reduces the stabil- 

 ity of the caoutchouc and renders it more readily oxidizable. 

 Numerous analyses failed to reveal any direct relationship be- 

 tween the percentage of nitrogen and the vulcanizing properties 

 of raw rubber. 



Dr. Stevens confirms Eaton and Grantham's observations that 

 a more rapidly vulcanizing crepe rubber is produced by allowing 

 wet coagulated latex to stand for a few days before washing 

 and drying; but he does not find any marked change in the 

 percentage of nitrogen, either in air-dried or smoke-dried rub- 

 ber from the same latex when subjected to the same detail of 

 preparation and lapse of time before vulcanization. 



Peptone, in its power to promote vulcanization, is roughly 

 equivalent to the natural protein matter, and consequently the 

 addition of peptone to a rubber already containing sufficient 

 nitrogenous matter for complete vulcanization will have a very 

 slight effect. Eaton and Grantham have show-n that heat-co- 

 agulable proteins, which separate on concentration of latex serum 

 have, when added to ordinary crepe rubber, no influence on the 

 rate of vulcanization. The natural insoluble nitrogenous mat- 

 ter, peptone and other complex proteins, must be sharply dif- 



