268 CHEMICAL DISCOVERY AND INVENTION 



pound are left behind in the residue. The nickel is recovered by 

 causing the mixed gases to pass through a heated pipe before 

 being returned to the furnace to play the same part over again. 



Very large quantities of nickel are also made from the mineral 

 called garnierite, which consists of a hydrated silicate of nickel 

 and magnesium and is found in New Caledonia. This mineral is 

 practically free from other metals, and the nickel is obtained 

 from it by a furnace process which consists in first converting 

 the metal into sulphide, and then reducing it by a series of opera- 

 tions similar in principle to those by which copper is obtained 

 from its sulphide ores. 



Nickel is a white metal a little heavier than iron but having 

 the advantage of practical permanency in the air whether dry 

 or moist. It is somewhat magnetic. The addition of nickel to 

 steel increases the toughness, and on this account nickel is em- 

 ployed in armour plate, as already mentioned in connection with 

 steel. 



LAMP FILAMENTS 



There must be a considerable number of persons still living 

 who remember the dim light with which the public of sixty 

 years ago had to be contented. Up to the time of the great 

 Exhibition in 1851, and for many years later, the interiors of 

 houses had been lighted by candles, and the snuffer tray was a 

 necessary article of daily domestic use. The streets of London 

 and of most towns were at the same time provided with lamps 

 for coal gas which was burnt at flat flame burners, giving a 

 degree of illumination which would be regarded as intolerable 

 at the present time. 



The discovery of large quantities of petroleum in Pennsylvania 

 about 1860 provided a new and cheap source of light, and there 

 was soon great activity among the lamp makers. The use of gas 

 as an internal illuminant for houses was still, previously to 1860, 

 though common, far from universal. 



With the development of various forms of magneto-machine 

 and ultimately of the dynamo which occupied many years, the 

 electric arc gradually became available for use in lighthouses, 

 and here and there for large spaces such as the Thames embank- 

 ment and in a few large workshops. But the arc was never suit- 

 able for domestic use, and it was only when the incandescent 

 lamp, with a carbon filament enclosed in a vacuous glass globe, 

 was invented that electric light became a practical source of 



