44 A. Killen Macbeth on 



to add on further hydrogen atoms. Finely divided metals prove 

 to be effective catalysts, and finely divided nickel is a most 

 effective agent. The general method now practised is to pass 

 steam over hot coke. Water gas — which is a mixture of hydro- 

 gen and carbon monoxide — is formed. The water gas is then 

 passed over nickel heated to about 100°C., and the carbon 

 monoxide reacts with the nickel, giving a volatile compound 

 known as nickel carbonyl, which, together with the hydrogen, is 

 passed into the hot oil. The nickel carbonyl is decomposed, 

 giving off carbon monoxide again and depositing rn'ckel in a very 

 fine state of division. This finely divided nickel acts as the 

 catalyst causing the hydrogen to combine with the oil. By this 

 method an oil may be hardened to any desired degree. Oils so 

 hardened are emx)loyed in the manufacture of soap and candles ; 

 they are also largely used in the manufacture of margarine. In 

 this latter connection it is interesting to point out that traces of 

 nickel remain in the hardened oils, and might have a harmful 

 effect if the oils are used for human consumption. No limit to 

 the permissible amount present has yet been fixed, but actual 

 experiments have been conducted with a view to examining the 

 effects of nickel compounds on health. As much as half a gram 

 of nickel oxide has been given daily in a diet without ill-effects, 

 99-8 per cent, of the metal being rapidly excreted : and hardened 

 oils contain very much less nickel than this, in fact, about one 

 hundreth of this quantity per pound. 



Synthetic Rubber. Since the introduction of the pneumatic 

 tyre the demand for rubber has gone forward by leaps and 

 bounds. The supply is derived from the sap exuded from the 

 barks of certain trees in the rubber plantations of Ceylon, Java 

 and elsewhere. It is not surprising that efforts were made to 

 })roduce rubber synthetically — that is, to prepare it by purely 

 manufacturing processes from simpler substances. Rubber, on 

 being decomposed by heat gives, amongst other products, a liquid 

 called isoprene. This liquid is also obtained from other sources, 

 notably turpentine. Sir William Tilden made a comprehensive 



