May I, 1909.] 



THE INDIA RUBBER WORLD 



277 



The Deresination of India-Rubber — I, 



By H. O. ChHic. 



IT is well known that all classes of cruilc rubbers contain im- 

 purities which affect their value, for nearly all the purposes 

 of manufacture. The amount of these impurities varies from 

 a small percentage in the best grades of plantation Ceylon to an 

 amount sometimes equalling 90 per cent, of the total in low-grade 

 Pontianak, and in general the value of a crude rubber decreases 

 proportionally to an increase in the amount of impurities. The^e 

 impurities are of two general classes. 



The first class consists of accidental, or mechanical, impurities, 

 such as water, sticks, stones, leaves, fibers, and such foreign sub- 

 stances as are removed in the processes of drying and washing 

 to which all rubbers are subjected, and their removal constituies 

 the ''shrinkage" which is always considered in valuing crude 

 rubber and which is negligible in the highest grades only. These 

 impurities, being easily removed by all. manufacturers, do not de- 

 preciate the rubbers to a greater e.\tent tlian their proportional 

 weight in the whole mass and the cost of their removal. 



The second class consists of chemical impurities, and comprises 

 the matters in the original latex, aside from the true gum, or 

 matters which are the product of decomposition or oxidation of 

 the gum. These are resinous bodies which are found in all crude 

 rubbers, and increase usually in amount as the rubber decreases 

 in value. Not being removable in the ordinary purifying treat- 

 ment, they are not only dilutants, but are of positive detriment in 

 many processes to which the gums may be applied. 



The amount of resins in crude rubbers varies greatly, as shown 

 by some analyses which have been published, giving the results 

 of testing various samples of the different varieties. The first 

 publication of value on this subject was made in the Journal of 

 the Society of Chemical Industry, by H. L. Terry, in 1889 (page 

 173). The following table shows the percentage of resins and 

 the melting point of various resins, and tlie remarks give further 

 description of resins: 



Name of Melting Remarks, 



rubber. Resin. Point. 



Para 1.2% 5*C. Dark brown color; soft and sticky. 



Ceara 1.3% 2*C. Yellow; soft and sticky. 



Columbian 2.5% .... Brown: dry. 



Mozambique 3.9% l8*C. "^'ellow; glutinous. 



Rio Janeiro 5-8% 64*C. Hard, powdery; yellow to white. 



Madagascar 6.1% .... _ Ditto. ^ 



Sierra Leone .... 7.4% .... Brown: contained glutinous body. 



Borneo 7.9% 28*C. Light brown; soft. 



Aicam n -iciL j S-3% I2*C. Vcllow ; sticky. 



-^"='"" 9-3^<'l4.o% 82'C. Hard, like shellac. 



Mangabeira 10.5% 48*C. Brown; brittle. 



.^frica^ ball (i)... 18.5% sS^C. Dark brown; of various melting points. 



.African ball (2)... 22.8% 2o''C. Ditto. 



African flake 41.2% 2o"C. Ditto. 



These figures were obtained after the rubber had been washed, 

 and therefore are based on dry rubber. They resulted from 

 cutting the rubber into fragments and extracting with go per 

 cent, alcohol in a Soxhiet extractor. 



It is said that these melting point determinations are not of 

 much value, as it is clear that the resins arc mixtures. It is to 

 be observed that these resins do not correspond with Spillei's 

 resin, which is an oxidation product of rubber, but these resins 

 are probably produced in the tree before the latex is collected, 

 and no amount of care will produce a rubber free from these 

 resins. 



Caoutchouc, which has undergone complete oxidation, consists 

 principally of a hard, brown, transparent substance, shellac-like, 

 called Spiller's resin. This resin is an acid, combines readily 

 with soda and potash, forming soaps whicli are soluble in cold 

 and hot water. Spillcr described this resin many years ago. lie 

 found it to contain 27.3 per cent, of oxygen. The chemical 

 formula CioH,oOa has been assigned to this resin, but this would 



correspond lo only 23.$ per cent., so that this cannot be the 

 correct formula. 



No one seems to have examined these resins to determine their 

 exact composition or chemical nature. It is particularly im- 

 portant to know what action takes place with the resins when 

 subrtiittcd to the processes to which rubber is treated. Of im- 

 portance in this connection is a report on the analysis of the 

 different brands of india-rubber by David Spence, ph. d., in 

 the Quarterly Journal of the Institute of Cominercial Research 

 in the Tropics, of Liverpool, in 1906 (pages 75-77). Some de- 

 tails from this are given here on account of tlie description of 

 the resins. 



"The rubber was cut up very fine and dried in an air oven 

 over calcium chloride at 55° C. until constant in weight. The 

 dried product was then extracted with acetone, the acetone ex- 

 tract being afterwards dried and weighed. 



"The residue left after exhaustive treatment with acetone was 

 again dried, and the caoutchouc was estimated in an average 

 sample of the resulting product by digesting the same with 

 chloroform until complete 'solution' of the caoutchouc took place. 

 The colloidal solution was allowed to stand until any coagulated 

 proteid had settled out, and was then filtered and the chloroform 

 evaporated. The thin film of pure caoutchouc obtained from the 

 chloroform extract was dried thoroughly over calcium chloride 

 and weighed. The residue insoluble in chloroform, which repre- 

 sents mineral matter, vegetable fiber, coagulated proteid, and in 

 some cases tlie so-called insoluble rubber, etc., was also weighed. 



"The following results were obtained for samples of the com- 

 mercial india-rubber before it had undergone any treatment: 



^foisture. Resin. Rubber. Residue. 



Grades. '/c '/< 'J, % 



I. Para, hard cure. .South .'\merica. . 14.30 2.73 71.00 11. 71 



J. Ceylon Para, Ceylon 0.53 3.93 90.38 5.03 



3. Gold Coast hard lump 8.74 19.72 69.22 a. 37 



4. Gold Coast soft lump 10.90 17.71 67.40 4.24 



5. Para rubber. Gold Coast 0.27 2.31 93.92 3.30 



6. Gold Coast niggers. Gold Coast.... 8.86 4.12 82.54 4.73 



7. Ficus Vogctii rubber. Gold Coast... 0.302 35.37 63.79 0.903 



8. Rangoon, Burma 0.58 6.81 84.63 8.16 



9. Lagos lump, Lagos 3.4 10.56 80.88 5.39 



10. Lagos root, Congo 3.0 3.34 73.35 23.51 



11. Congo root, Congo 2.30 7.02 83.00 7.74 



12. Sierra I-eone niggers (a) 5.3 5.54 80.46 9.05 



13. Sierra Leone niggers (b) 2.9 4.97 65.5 26.40 



14. Pcrnainbuco scrap 4.8 4.35 58.75 32.31 



RESIDUE. 



Insoluble rubber. 

 Insoluble rubber. 

 Insoluble rubber; bark. 

 Insoluble rubber: fibrous material. 

 \'ery little insoluble rubber. 

 Largely proteids and some mineral 

 matter. 



Bark, small quantity insoluble rubber. 

 Largely fiber. 

 Root, fiber, sand. 

 Root and fiber. 



Bark and other impurities. 

 Insoluble rubber and bark. 



RESINS. 



1. Soft, oily. 



2. Hard, glue-like. 



3. Hard but non-crystalline. 



4. Hard. 



5. Soft and oily. 



6. Hard and dry. 



7. Hard, clean, dry. amorphous. 



8 



9. Soft and glue-like. 



10. Hard, dry. amorphous. 



II 



12. Fairly hard but glue-like. 



13. Fairly hard. 



14. Hard but not amorphous. 



The variability of the amount of resins which may be founJ 

 in the various classes of rubber is illustrated by the results of 

 analyses made by Lyman M. Bourne [see The India Rubber 

 World, December l, 1906 — page 75.] His table covered 181 

 analyses of all classes of rubber, and the results of a few of the 

 more important are given here. 



Three samples of Ceylon Pari fine averaged 2.5 per cent, resin 

 and 97.5 per cent, rubber with no shrinkage, this being the only 

 variety without shrinkage. The average of 23 samples of 

 Brazilian Para fine showed 96.6 per cent, rubber and 3.4 per 

 cent, resin, with 17 per cent, shrinkage. Six sample? of prime 

 Assam, from India, showed 15.8 per cent, resin. Two samples of 

 Borneo second an<l one of Borneo third showed 19.3 and 20.7 



