244 



THE INDIA RUBBER WORLD 



January 1, 1921 



taken from the machine and wrapped witli strips of wet cloth to 

 protect the top tlap from the steam while curing. 



The advantages of curini; Haps in drums are numerous. First 

 the flap is given both curves in one operation, thus insuring that 

 ^he llap will exactly tit the rim and tire. Second, on the average 

 curing drums approximately 50 llaps can be cured at one time. 

 The average drum is about three inches in width, which permits 

 many drums to be placed in a vulcauizer in the same heat. 



The flap-making machine is driven by a direct-connected one- 

 horse-power motor or from an overhead shaft and is speeded to 

 produce 6,000 feet of flap per hour, cither four or five ply. 



CURING DRUMS 



The curing drums upon which tlie flap as produced by the build- 

 ing machine is received are built of steel. They are so con- 

 structed, as shown in the illustration, that they give the proper 

 curves to the flap, thus insuring its fittin.s; the tube as well as the 



tire. 



The drums are about 30 inches in dianioti-r. divided into sec- 

 tions through the center and held togcthor with thumb screws. 



Dexter Flap Lurinx. Drums 



This feature provides for greater ease in handling the strips of 

 flap stock after curing, without unreeling. 



THE OLDEST PIECE OF RUBBER IN THE WORLD 



The extensive use of rubber is so decidedly a development of 

 later years that we are prone to consider it a substance of com- 

 paratively recent discovery. History refutes this, however, as 

 Columbus, during his second visit to the new world in 1493-96, 

 saw the natives of Haiti playing a game wTth balls of "gum," and 

 it is also recorded that natives of Mexico played with rubber balls 

 at the time of the advent of emigration from Europe. 



The oldest piece of manufactured rubber in the world, in the 

 belief of Francis E. Lloyd, professor of botany at McGill Uni- 

 versity, Montreal, Quebec, Canada, was discovered in December, 

 1909, in some excavations for a dam near Sasco, Arizona. While 

 digging in an off-wash from an adjacent mountain, an earthenware 

 jar was uncovered three feet lielow the surface, in which lay a ball 

 of rubber together with some stone implements recognized by 

 archeologists as belonging to the older prehistoric ruins of the 

 country. The ball is shrunken, with cracked, hard surfaces in- 

 crusted with a sort of light buflf-colored plaster. The cut surfaces 

 are black and show a definite banding. The interior looks and 

 feels like a quite good sample of ordinary crude rubber. Sur- 



rounding this is a dark shiny band, tacky and apparently resinous. 

 Bubbles of air can be seen scattered in the mass of still preserved 

 rubber. 



The origin of this ancient plaything; is a matter of conjecture. 

 .■\s it was fuuiul in a rt'cion similar In that in which guayule 



/>p Ml (It (en 



.•\ Prehij^toric Rubber Ball 



rubber is produced, it may be that substance. It may even have 

 come by devious ways from far away South .\merica. But what- 

 ever its origin the rubber has stood the tests of lime almost as 

 immutably as stone. 



SOME MICROSECTIONS CUT FROM VULCANIZED 



RUBBER ARTICLES' 



By Harlan A. Depew and I. R. Ruby" 



IT has long been recognized that pigments for use in rubber 

 work should consist of very fine particles. 



Microscopic work done in this laboratory on pigments in lin- 

 .seed oil. and other paint vehicles has shown that fine particles 

 tend to exist as flocculates. In certain vehicles this flocculation 

 is largely or entirely overcome. In the case of water suspensions, 

 as well as of paints, the physical properties of a deflocculated 

 and a flocculated suspension dififer greatly. 



Carr\ing the suspension analogj- still further to the very much 

 more viscous (properly, plastic) medium, rubljer, it seems reason- 

 able to assume that dispersion and flocculation of pigments play 

 important parts in determining the physical properties of com- 

 liounded rubber. 



Attempts to detcnninc the dispersion of pigments in com- 

 pounded rubber by reflected light have failed, because with the 

 high magnifying powers necessary to see the individual par- 

 ticles of, for example, zinc oxide or carbon black, the illumina- 

 tion of the surface is entirely too weak, particularly where the 

 reflecting properties of the medium and the suspended pigment 

 are close. Our success with transmitted light in water and oil 

 suspensions pointed to tiiis method of illumination for the ex- 

 amination of compounded rubber. 



There is considerable difficulty in cutting sufficiently thin sec- 

 tions of vulcanized rubber, owing to its elasticity and toughness, 

 especially in the case of rubber highly compounded with zinc 

 oxide or carbon black, where the thickness must not exceed one 

 A.' In less highly compounded matter the section can be 20 i^ 

 thick, or even thicker. The elasticity' can be destroyed by im- 

 mersing in liquid air, but this makes the sample too hard to cut. 

 .\ccordingly, the rubber must be frozen to an extent just suf- 

 ficient to destroy its elasticity and yet not make it too hard. 



'Rcart before the RnWicr Division of tlie American C'liemical Society, 

 Cliicago, Illinois, Scptcmher 6-10. 1920. 



^Research Laboratory of the New Jersey Zinc Co.. Palmerton, Penn- 

 sylvania. 



"One n equals 1/1000-millimetrr. 



