April 1, 1916.] 



THE INDIA RUBBER WORLD 



345 



that the correct factor for calculating the protein content of 

 plantation and wild Para rubber is 10 rather than 6.25, which 

 has previously been taken. 



The process of isolating the nitrogenous composites of rubber 

 also permits their further study and analysis. 



The details of the method are thus stated : 100 grams of 

 washed and dried rubber are treated with 1,000 cc. of benzene 

 containing from 0.3 to 0.5 per cent of trichloracetic acid. The 

 mixture is exposed to sunlight or heated in a vessel immersed 

 in boiling water and thoroughly shaken at intervals. After 

 48 hours the solution is allowed to settle and the clear liquid 

 decanted. The insoluble is subjected to two extractions, 500 

 cc. each, of the mixture of benzene and trichloracetic acid. The 

 residue is washed with pure benzene, dried, powdered and again 

 extracted with benzene. Following this it is washed with alcohol, 

 dried and weighed. 



THE STRUCTURE OF RUBBER. 



In "Le Caoutchouc & la Gutta Percha" (February IS, 1916) 

 .-Xndre Dubosc discusses at length the various theories of the 

 structure of the rubber molecule and its attachments in the 

 complex rubber agglomerate. The author recognizes the ex- 

 treme difficulty of the problem, and reviews impartially the 

 work of the eminent chemists who have investigated the sub- 

 ject. He presents a concise discussion of the leading theories, as 

 analyzed by the Russian chemist Koudhakow, and sustains the 

 theorj' of Barrow as the best thus far advanced. 



Barrow holds that no formula of the constitution of rubber 

 can be admitted unless it is compatible with the following ex- 

 perimentally demonstrated facts : 



1. Rubber gives, by action of ozone, an ozonide which results 



from the addition of 0^ to a product of depolymerization. 



2. Rubber, treated with bromine, gives a tetra bromide, which is 



an addition product. 



3. Rubber, heated in high boiling point solvent, depolymerizes, not 



to a cyclooctadiene, but to dipentene containing a cycle 

 in C. 



4. Rubber subjected to pyrogenation gives a series of products 



of decomposition. 



5. Rubber, by hydrogenation, changes into a saturated carbide. 



6. Rubber can be obtained by polymerization from isoprene, 



whereas the dipentene does not give rubber. 



7. Rubber, left to itself, passes by a superior degree of polymeri- 



zation, this process being reversible. 



8. A small quantity of sulphur is sufficient for complete vulcan- 



ization. 



Barrow proposes a very ingenious formula, which practically 

 harmonizes the ideas of Harries and Pickles. This he has done 

 by the conception of a spiral formula for the rubber complex, 

 with double connections mutually saturated. The diagrams 

 (here omitted) show that such a spiral molecule would be in 

 close relation with that of the cyclooctadiene, since the double 

 connections are in the same situation. 



Harries' formula explains the rubber molecule, but is vague 

 regarding complex or polymerized rubber. 



Barrow's spiral formula scheme supplements Harries' theory 

 by uniting and explaining the reactions that have been experi- 

 mentally noted concerning rubber, and gives the best idea of 

 what the structure of rubber may be, notwithstanding certain 

 obscure points and the difficulty of comprehension that the 

 scheme involves. 



ACETONE SUBSTITUTE. 



Solvent mixtures containing ethyl alcohol, ethyl acetate and 

 formic ethers have been proposed in place of acetone for the 

 treatment of resinous rubbers by extraction. The presence of a 

 large amount, 40 per cent, of ethyl acetate in such a solvent 

 serves to hold considerable of the rubber in solution. This 

 action is aided by the heat, which increases the reaction of the 

 acetic and formic ethers upon the rubber. The solution thus 



formed can only be precipitated by the addition of a large 

 quantity of ethyl alcohol. 



The use of such acetone substitutes is not economical, and can 

 not be recommended. (G. Noyer in "Le Caoutchouc & la Gutta 

 Percha.") 



A NEW METHOD OF COAGULATION. 



Eaton and Grantham, chemists of the department of agricul- 

 ture of the Federated Malay States, have published in the 

 "Bulletin" (November, 1915) an account of their experiments 

 on the coagulation of Hevea latex and a new method of 

 coagulation : 



"If Hevea latex be allowed to stand in open vessels, the 

 amount of coagulation depends on the shape of the vessel and 

 the depth of the latex. A thin layer of latex does not coagu- 

 late, but changes to a peculiar slime with a yellow surface 

 scum. If latex be placed in tall cylinders, coagulation is much 

 more complete and the slime formation is much less, constitut- 

 ing only a small depth of the latex near the surface. The surface 

 scum is also found to be alkaline in character and the scum 

 below acid, showing two distinct processes of decomposition. 

 This is the basis of the so-called "anaerobic" process of coagu- 

 lation for which a patent has been taken out in the Federated 

 Malay States. This process may thus be explained by a 

 bacterial theory. The conditions are such as to inhibit a large 

 number of bacterial species, including most of the putrefactive 

 ones, while other species, including the coagulating ones, free 

 from the competition of purely aerobic species, are encouraged. 

 To find an explanation on the enzymic hypothesis is more dif- 

 ficult. We have since found that coagulation under these con- 

 ditions is variable, on some days the coagulation being com- 

 plete and on other days not quite complete, indicating a variable 

 factor in the latex itself." 



A series of experiments was conducted in which the effect 

 of putrefactive and non-putrefactive changes in the latex was 

 studied. Treating latex with various antiseptics and heat de- 

 layed or prevented coagulation. 



The authors summarize their experimental results as follows : 



"These experiments indicate a possible explanation of the 

 natural coagulation of the latex of Hevea BrasiUcnsis, viz. : That 

 it is due to certain bacteria which infect the latex after col- 

 lection. 



"There are two distinct types of organisms, one favored by 

 aerobic conditions, which tends to inhibit coagulation and pro- 

 duces an alkaline slime in the presence of air, and the other 

 favored by anaerobic conditions which affect the coagulation of 

 the latex. 



"The coagulation of latex under anaerobic conditions is not 

 constant; on some days complete coagulation occurring, and on 

 other days being much less complete, possibly due to a variation 

 in the constituents of the latex. 



"By the addition of various sugars, coagulation under both 

 aerobic and anaerobic conditions always occurs, and is caused, in 

 our opmion, by the fact that a medium is formed more favorable 

 for the organisms which produce coagulation, and less favorable 

 to those producing putrefactive changes." 

 ANALYTIC METHOD. 



Determination of Total Chlorine in Rubber Sitbstitute. — 

 The method of A. Hutin is as follows : From 0.2 to 0.5 grams of 

 the substitute is covered in a porcelain crucible with the usual 

 mixture of sodium carbonate and potassium nitrate. The mixture 

 is heated slowly to quiet fusion. When cold the melt is dis- 

 solved in water to which nitric acid has been added, and the 

 chlorine determined by titration. 



Should be on every rubber man's desk— Crude Rubber and 

 Compounding Ingredients ; Rubber Country of the Amazon ; 

 Rubber Trade Directory of the World. 



