KNOW I.I I If, i: 



MARrii. 1912. 



The l-lowcr 



and several niamifactnrcrs also re-wash ami dry 

 plaiitatiiin rul)l)t"r. though this repetition of the 

 process is not really necessary. After washing and 

 drying, the rubber is compounded with various 

 mineral matters, and vulcanised by conibining with 

 it a small (juantitv of sulphur. 

 This vulcanisation renders it 

 tougher and chemically more 

 inert. X'ulcanite itself is manu- 

 factured by combining rubber 

 with a much larger (juantitx' of 

 sul|)hur. 



The wasliing process frees tin 

 rubber from all mechanical 

 impurities, such as pieces ol 

 wood, vegetable fibres, and so on. 

 and also any soluble impurities. 

 The product obtained is des- 

 cribed as technically })ure, hut it 

 is not chemically pure. Besides 

 pure rubber, or caoutchouc, it 

 contains various resinous, albu- 

 minous and mineral matters, as 

 well as small quantities of an 

 oxvgen compound discovered by 

 Dr. Weber,* possessing the 

 empirical formula Ci.r, H^j C)-. 

 In para rubber, the amount of 



resin varies from one to four per cent.: but in 

 certain low grade rubbers it may reach as much as 

 forty per cent. The resinous matter is renuned. for 

 purposes of analysis, by extraction witti acctonr. Tlu- 

 separation of theproteidsor 

 albuminous matters is best 

 performed by centrifuging. 

 The percentage of mineral 

 ash left after combustion 

 is generally very small. 



Pure rubber, or caout- 

 chouc, is a hydrocarbon 

 w ith the empirical formula 

 C-, H„. Its molecular 

 weight is not known, hut 

 that it is very high may 

 be safeh' concluded from 

 the properties of the sub- 

 stance. Its true formula. 

 therefore, is some lui- 

 known multiple of C., H„; 

 in consequence, it is 

 written (C., Hfjii.^ Its 

 colloidal nature renders it 

 a difficult body to study, 

 since like other colloids 

 it possesses no definite melting point or soluiiility 

 moreover, it is not a cheniicallv active boib 



In the sense that sugar is soluble in water, 

 caoutchouc is not soluble in any liquid. When, 

 however, certain fluids (t'-j!,'., petroleum spirit, 

 benzene, carbon disuli)hide, and .so on) are poured 

 on to rubber, it swells very much, fcjrming first a 

 jelly, and ultimately a very 

 viscous fluid. That the pn^duct 

 is not a true solution of rubber, 

 but rather a solution of the so- 

 called solvent in rubber, is 

 e\ident from the fact that on 

 the further addition of tlif 

 ■' solvent " to the fluid jelly, the 

 latter tends to separate out. 

 Certain other fluids, such as 

 water, alcohol, and so on, which 

 do not form fluid jellies of this 

 sort with rubber, are gradually 

 absorbed by it, wa*er to the 

 extent of twentv-five per cent., 

 alcohol to that of twenty per 

 cent., the rubber becoming much 

 distended in the process. 



On the dry distillation of 

 rul)ber, various hvdrocarbons. 

 all ijosscssing the empirical 

 formula CjHg, and belonging to 

 the gnnip of substances know n as 

 "terpenes." are obtained. These include Isoprene 

 (Meth\l divin\l), C-.H^: Dipentene (at one time 

 known as caoutchenc). CigHig: Heveene: and certain 

 '\ ttrpciies. Dr. Weber gives the following table, 

 showing the result of dis- 

 tilling three kilogrammes of 

 carefully washed and vacuum- 

 dried para rubber. 



per cent. 

 Isoprt-nc 

 Dipentene 

 Heveene 

 Polyterpenes ... 

 Carbon residue 

 Mineral residue 

 Loss (water and 

 (jases) 



43 



= 1-4 



6 



I'lorui-; Sft. 



Mutluuls c.f Tai)piii.L;. 



niii;-!)..!,,- l; Hall 1 iL-rrin^-boni' 



hirmul; 



Hasal V. 

 CH-,, 



(3f these products iso- 

 prene is the most interest- 

 ing, because it polymerises 

 spontaneouslv, partly into 

 di[)entene and partly into 

 caoutchouc. Isoprene 

 is a colourless liquid, boil- 

 ing at ■i?''' under normal 

 atmospheric pressure. 

 It has the constitutional 



r-Cll ril, 



JiiiiiiKil ()/ the Society 



>/ Chciiiicdl Industry. 1900. See also C:u\ Otlo Wi-ln 

 Kiiiiber ■' ( 1 902), pages 7-11. 



rii.n.. ■■ riic rheiMisUv of India 



' Gladstone and Hibbert ijoiinial of the Clu'iiiicirl Society, 18SS) concluded from an examination of the refractive index 

 of rubber solution that caoutchouc contains three ethylene bonds, and that, therefore, the simplest formula possible for it 

 is tin Hi„. Tluir evidence, however, is not conclusive, owins; to the method of calculating molecular refracti\ ities employed. 



