106 THE ALUMNI JOURNAL 



sticks are again clipped into the collected juice and then heated in the 

 same manner ; the process being kept up until a large roll or loaf of 

 rubber is obtained. This constituted the crude rubber of commerce. 

 It has a characteristic odor somewhat resembling pyroligneous acid, — 

 This odor is developed by the heating process, to which it is subjected. 



The Para rubber is the best of all varieties. 



The chemical composition is chiefly that of a terpene (CioHje), 

 but its molecular composition is unknown. The formula given by 

 Prof. Toch is (C]oHio)i^. 



The research work on this useful substance is limited, there being 

 only about four books on the subject. 



Clouths. (German), "Rubber, Giitfa Perca and Balata" ; Pearson 

 on Rmv Material; Hinriques "Analysis of Rubber" and C. O. Weber, 

 "Chemistry of Rubbef. 



The Journal of the vSociety of Chemical Industry, (of Great Brit- 

 ian), also offers quite some contributions of value on this subject. 



Rubber substitutes may be made by vulcanizing some of the more 

 common fixed oils such as rape seed, cotton seed, or linseed, with sul- 

 phur chloride in the presence of a catalytric agent as manganese, lead 



or zinc compounds. 



RUBBER SUBSTITUTES. 



The "bloom" generallv found on rubber articles of commerce is 

 due to minute particles of sulphur coming to the surface. A solution 

 of sodium hydroxide and glycerine will be found beneficial in its re- 

 moval. 



It comes to the market of the world in the form of balls or loaves. 



The Para varieties consist of about 98% of terpenes and only 2% 

 of resin, while some African varieties yield as high as 41% of resin. 



Rubber is sheeted by passing it between roller cylinders, which 

 also rids it of soluble salts, such as nitrates, nitrites, sulphates etc., an 

 essential feature. 



The pure article has a specific Gravity of 1920 — ^925 and therefore 

 floats when thrown into water. A "filled" rubber has a higher gravity 

 and wall on this account sink in water, thus affording a simple means of 

 distinguishing between them. 



It is an absorber of water and is therefore not water-proof, but 

 it is damp-proof. It will absorb about 25% of water. If the water 

 is hot, it will soften the rubber and also combine with it chemically, 

 while cold water will neither soften it or combine with it. 



