Jink 1. 1915.] 



THE INDIA RUBBER WORLD 



483 



Substitutes for Hard Rubber. 



CHARLES GOODYEAR, in discussing hard nil, her. the 

 invention ol Nelson Goodyear, is said to have char- 

 acterized it as a material so unique and valuable that 

 u would never i i ssfullj counterfeited. Nearly 70 years 



Boonton Rul 



\ii banical Testing Apparatus fur Bakelite. 



have passed and his prophecy lias been strikingly verified. 

 Whether crude rubber has been sold at 50 cents or $3 a 

 pound, bard rubber manufacture has not onlj continued but 

 the business has shown a steady growth. While vulcanite has 

 not had the wide range of usefulness that soft rubber has 

 enjoyed, its field is a wide one. It is the insulator most de- 

 sired for electrical instruments of all sorts in telegraph, tele- 

 phone and wireless lines. It finds also a special use in sur- 

 gical and stationers' goods, in scien- 

 tific apparatus, in sporting goods, in 

 high pressure valves and packings. 

 in acid pumps and utensils, and 

 scores of minor lines. In all of these 

 lines substitutes have been produced 

 — some with a considerable degree 

 of success, due. as a rule, to the 

 low price at which they could be 



marketed 



Hard rubber ha, so many valuable 

 properties that it cannot be said that 

 any substitute possesses all of them. 

 A number have some of them, and 

 in many cases these properties are 

 sufficient for requirements for er- 

 tain purpose. 



The superiority of hard rubber for 

 insulating purposes was early recog- 

 nized. In addition to the higher cost 

 of vulcanite, its deterioration when 

 exposed to light has been mentioned 

 as an argument against its use 



In the Bureau of Standards at 

 Washington a sample was kept in 

 diffused light for a year and a 

 marked deterioration in its insulating 



capacity was noted on testing, i In exposure to sunlight for 

 about six months it had deteriorated more than in the pre- 

 vious year. 



Various methods of cleaning the surface were tried. Rub- 

 bing with oil improved it. but not as much as desired. Caustic 

 soda Improved the appearance but not the insulating qualities. 



Finally, it was found that by soaking in water for two days 

 the resistance became greater than in the original sample, on 

 account of the rougher surface. I." u fortunately, this experi- 

 mental sample contained a large amount of filler besides the 

 rubber and sulphur. The nature of this filling material was 

 n.t determined or disclosed. It is quite likely, therefore, as 

 suggested in the record of tests, that soluble sulphates were 

 formed on the surface from oxidation of the sulphur in com- 

 bination with tile idling. 



INSULATING MATER] \l S. 



\\ bile insulating materials such as mica, porcelain and glass 

 do not possess the toughness and elasticity of hard rubber, 

 the) are used as substitutes because of their cheapness. 



Rubber is by far the best binder for any sort of molded in 

 sulatioti Shellac, however, is extensively used, with fillers 

 to give strength or to improve the fireproof qualities. Shellac 

 hi- risen so in price that of late it has been displaced by 

 cheaper gums, such as daniar, rosin and the asphalts. These 

 gums are melted, then put into a mixing machine with the 

 tillers, taken out and rolled into sheets, which latter operation 

 closelv resembles ordinary rubber mixing. The sheets are 

 cooled and broken up, softened and put into hot molds, 

 pressed, cooled and emptied out as finished product, ^nothei 

 method is to dissolve the binding material in a solvent, mix 

 with the tiller, cool and then remove and dry. When the 

 product becomes hard it is ground to powder. This is placed 

 in heated dies and pressed till melted, then cooled in the die 

 and removed in finished condition. There being no vulcaniza- 

 tion, it is evident that only those binders can be used which 

 are plastic when hot and solid when cold, and that if heated 

 while in use to the fusing point the binder- will -often and 





Chemical Laboratory in \ Bakelite Plant. 



be worthless. \ large percentage of fillers, however, will 

 stand high heat for a short time. Ordinary asphalts, pitches 

 or bitumens are not suitable for this work, as they soften at 

 too 1. iw a temperature. 



Rosin, while the cheapest gum, also melts at the lowest 

 temperature and therefore is the most unsuitable. Rosin 



