PART II. 



CHAPTER III. 



TUNGSTEN. 



Properties. 



Tungsten is a metallic element which gives rise to acid-forming 

 oxides ; it forms salts with several metals such as iron, manganese, 

 calcium and lead. It is never found native but must be reduced 

 from its ores to the metallic condition by chemical means. The 

 mineral wolfram must have been noticed in the older tin mines of 

 the world centuries ago, but it was not until the year 1781 that the 

 Swedish chemist Scheele discovered a new acid in the mineral 

 " Scheelite." To this the name tungstic acid was given later. 

 It is derived from two Swedish words, " tung "=heavy and " sten " 

 =stone. In 1783 the brothers D'Elhuyart proved that wolfram 

 also contained tungsten, established the relationship between scheelite 

 and wolfram and were the first to prepare the metal. 



Its atomic weight is 181 and it is harder than glass. The specific 

 gravity of the pure wrought metal is 18*81. Its melting point is 

 said to be 3,267° C. (Longmuir and Mackay). Its tensile strength 

 greatly increases on working and it can be drawn into very fine wire. 

 Metallic tungsten is comparatively inert, it is almost unaffected by 

 air or water at ordinary temperatures but it oxidises when heated in 

 air. It is only acted upon slowly by the common acids but is 

 rapidly attacked by fused oxidising salts, such as alkaline nitrates 

 and peroxides. It alloys with many of the common metals and 

 with cobalt and chromium forms one of the group of alloys known 

 as stellite. 



When treated with hydrochloric acid the tungsten minerals 

 dissolve leaving the yellow trioxide, W0 3 . On adding metallic 

 zinc or tin to the acid solution, this trioxide is reduced and the solu- 

 tion turns blue owing to the formation of a lower oxide. On further 

 reduction purple and brown compounds are produced which contain 

 less oxygen. 



