October 1, 1910.] 



THE INDIA RUBBER WORLD 



increase, and it was in the hope of determining which of these 

 ninerals were effective that the experiments enumerated below 

 ivLTC carried out. In order to observe more clearly the effect 

 whicli the various minerals exert on the resins during vulcaniza- 

 tiiin. the more common minerals were added in varying amounts 

 to a standard rubber compound and the increase in the resin 

 content determined analytically. The basic compound consisted 

 of 100 parts of rubber and 8 parts of sulphur. A series of com- 

 pounds were mixed up containing rubber and sulphur in the 

 identical proportions but with varying percentages of zinc oxide, 

 litharge, lime, calcined magnesia, white lead, barytes and whit- 

 ing. These minerals were added in percentages based on the 

 rubber. For instance, a typical compound would read as follows : 



Rubber, 100 parts : sulphur, 8 parts, and litharge, 5 parts. 



Or again : 



Rubber, 100 parts: sulphur, 8 parts, and zinc, 20 parts. 



In this manner tlie effect produced by the various minerals 

 could be noted reaaily with a minimum of calculation. Of course. 



more marked as the amount added increases up to SO per cent. 

 Zinc also seems to follow the same rule in that the resin content 

 decreases with the amount added, whereas in the case wiierc zinc 

 oxide and litharge were both present, decrease in the resin con- 

 tent is about the same as would have been produced by the 

 litharge alone. The cases of lime and magnesia are very interest- 

 ing, even the relatively small amounts of 5 per cent producing 

 very marked decreases. 



An explanation of the above observations is hazardous, in view 

 of the limited amount of experimental data. It is at once ap- 

 parent, however, that the substances which bring about decreases 

 in the resin content are all of a basic nature, and the two materials 

 which are particularly active, namely, lime and magnesia, have a 

 relatively strong basic nature. In view of the known fact that the 

 resins from Hcvea rubber are in part saponifiable, it seems reason- 

 able to suppose that salts have been formed in the vulcanizing 

 process between the saponifiable resins and the mineral oxides, 

 with the formation of acetone insoluble metallic resinates. It is 



Dr. Loth ar E. Weber. 



He.vrv C. Pe.\rso.v. 



Dr. T. B. Ti'TTi.E. 



in each case the resin content is based on the actual amount of 

 rubber present. For the sake of convenience all samples were 

 cured in the press at 45 pounds pressure for various periods, de- 

 pending on the nature and amount of mineral added. 



The following table shows the changes in the resin content of 

 the crude rubber, the crude rubber vulcanized with sulphur alone, 

 and the compounds containing rubber, sulphur and minerals in 

 various proportions. 



Crude rubber gave resin content of 3.54 per cent. 



100 parts rubber and 8 parts sulphur gave resin content of 3. S3 

 per cent, based on rubber present. Additions of minerals as fol- 

 lows gave percentages based on rubber present : 



5 per cent litharge gave resin content Z.6 per cent 



10 pi-T cent litharge gave resin content 2.8 per cent 



20 per cent litharge gave resin content 2.7 per cent 



50 per cent litharge gave resin content 2.1 per cent 



20 per cent zinc oxide gave resin content 3.4 per cent 



50 per cent zinc o.xide gave resin content 3.1 per cent 



20 per cent -.vhite lead gave resin content 4.0 per cent 



.. ll^V^r^'lS^^.^'] resin content 5.6 per cent 



5 per cent lime gave resin content 2.5 per cent 



5 per cent calcined magnesia, resin cent. 2.6 per cent 



50 per cent whiting gave resin content 3.5 per cent 



50 per cent barytes gave resin content 3.7 per cent 



These figures are iiideed surprising and directly in contradic- 

 tion to what one would have expected. There is a much more 

 marked decrease in the resin content than increase. To be sure, 

 barytes and whiting are without effect one way or the other. This 

 is more or less what one would have expected in view of their 

 inert action in the vulcanization process. The addition of 20 per 

 cent of white lead is the only case where there has been any ap- 

 preciable increase. Even in this case the increase is so very small 

 as tfp just lie outside the limit of analytical error. It is mteresting 

 to note the action of litharge. When added to the extent of only 

 5 jierccnt no change in the resin content is observed. There is a 

 marked decrease on the addition of 10 per cent, which becomes 



not improbable that a connection exists between the action of these 

 minerals on the resins and the accelerating action which the 

 former produce. This seems the inore probable, in view of the 

 fact that the elimination of the resins from the crude rubber 

 practically inhibits vulcanization. 



As already stated, the above samples were all vulcanized in the 

 press, a fact which should be clearly borne in mind. The samples 

 are at present being vulcanized in live steam and will doubtless 

 show increased resin content on analysis. To be sure the intro- 

 duction of live steam brings forth another factor into the vulcaniz- 

 ing process. From the above figures, however, it would seem, 

 in tlie presence of metallic oxides, as if the primal tendency of 

 vulcanization were rather to decrease the resin content than to 

 increase it, probably owing to the formation of metallic resinates. 



THE RUBBER CHEMIST AND THE RUBBER TRADE, 



Mr. Pearson's address, in brief, was as follows: 

 As a text to my address I want to use a brief letter re- 

 ceived this month from an old-time rubber superintendent — 

 a man who has had an unusual measure of success, who is 

 absolutely honest but thoroughly of the old school: 

 To THE Editor of The Indi.\ Rubber World. 



Dear Sir — A considerable space of every edition 

 of your valuable magazine is given to "What the 

 Rubber Chemists Are Doing." 



It has been my privilege to talk with several man- 

 agers and invariably each has a problem. When 

 asked why not let the chemist work it out, tliey 

 answer they have tried and failed to find the solu- 

 tion. Now is it true that chemists are of any ad- 

 vantage or only a fad, same as the game of efficiency 

 that has been taken up by many, but is being gradu- 

 ally dropped? Chemistry and efficiency have their 

 place in the world's work, but a good practical man 



