THE ALUMNI JOURNAL 107 



In 1832, Reidstorf made the discovery that combining sulphur 

 and rubber, gave a non-sticky product. 



Goodyear likewise obtained a hard rubber — vulcanized — when 

 these substances were heated together. 



Rubber does not, as is commonly thought, dissolve in solvents as 

 carbon-disulphide, but rather the reverse — the carbon disulphide dis- 

 solves in the rubber. 



VULCANIZED RUBBER. 



It is vulcanized by combining with it sulphur in varying propor- 

 tions and at a temperature of about 315 °F. This sulphur combines 

 as a solution. If the rubber article be bent a very fine deposit will 

 be noticed to come to the point of bending. This deposit when ex- 

 amined under the microscope will be seen to consist of small crystals 

 of sulphur. 



Too great an excess of sulphur is liable to produce brittleness. 



RUBBER COLOURING. 



For red rubber, sequi sulphide of antimony ( Sb. S,) is used to a 

 great extent ; for producing a chocolate color sulphide of iron is 

 used. 



FILLERS. 



The products contain a varying quality of "filler", for instance, 

 "Floor-tile" consists of only 8% of rubber and 92% of filler and is very 

 resistable to wear. 



White lead has been used as a filler but yields a spongy mass, 

 "Sublimed Lead" is now more used for this purpose, and consists of 

 lead oxid, 20 parts, lead sulphate. 75 parts and zinc oxid, 5 parts. 



The inner tube of an "Auto" tire contains zinc oxid and an iron 

 oxide ( Fco O,). It is highly elastic and retains the air, while the 

 outer tube of the tire consists of about eight layers of duck, 50% 

 vulcanized rubber and 50% of filler, giving an extremely resistable 

 protective covering for the inner tube 



Large quantities of silica or heavy spar ( Ba S O4), are used in the 

 manufacture of rubber goods. Some white rubber-tubing has been 

 found to contain as much as 7% of zinc oxid as filler. 



The various fiillers are zinc oxid (Zn O), gypsum (Ca SO4), 

 whiting (Ca CO;,), talc, magnesium carbonate, heavy spar (Ba SO4). 

 silica and litharge. 



