270 CHEMICAL DISCOVERY AND INVENTION 



though the presence of a small quantity of carbon renders it 

 brittle. The Osram lamp contains a filament of practically 

 pure tungsten, which is said to be produced by mixing the powder 

 of the metal with some binding material and then squirting it 

 into threads by forcing it through a fine hole in a steel plate. 

 The threads are subsequently treated by a secret process to 

 remove the binding matter and produce a continuous thread. 



Tantalum was discovered by Ekeberg in 1803. It was found 

 in two Swedish minerals, tantalite and yttro-tantalite, but until 

 the electric furnace provided the high temperature necessary it 

 had not been melted and was known only in the form of a black 

 powder. Tantalum is a white metal with a specific gravity 16-8. 

 It melts at a very high temperature, said to be 2798 C., accord- 

 ing to tests made in 1912 at the University of Wisconsin. It is 

 malleable and ductile at a red heat, but like many other metals 

 the presence of impurities, especially carbon, renders it brittle. 

 It resists the action of most acids, and, considering the present 

 very high price of platinum, its employment for making crucibles, 

 dishes, and other chemical vessels seems likely to extend. 



PYKOPHORIC ALLOYS 



A return to the flint and steel with the tinder-box of our fore : 

 fathers is improbable for everyday purposes, but the discovery 

 of the property exhibited by cerium and some of the other metals 

 of the same group of so-called rare earths (see periodic scheme of 

 the elements, p. 125) has led to the invention of contrivances for 

 striking fire which are occasionally useful and are certainly 

 curious. 



The metal cerium, obtained by the electrolysis of its chloride 

 or fluoride, resembles iron in appearance but is far more fusible 

 as it melts at 623 C. It is also much more easily oxidisable, 

 decomposing water slowly, and in moist air it soon becomes coated 

 with a film of oxide. The metal burns when ignited even more 

 brightly than magnesium, and when scratched with a steel edge 

 or struck by a flint it emits brilliant sparks. This property has 

 been turned to account in the production of gas lighters and 

 cigarette lighters for the pocket. Pure cerium is, however, l^ss 

 suitable for this purpose than certain mixtures of the cerium 

 metals with iron, which are harder and yield sparks much more 

 readily. An alloy of cerium with magnesium and aluminium 

 when heated below the melting point in a stream of hydrogen 



