CHROMIUM, MOLYBDENUM TUNGSTEN, URANIUM, ETC. 291 



in Saxony, Sweden, and Finland. Tungsten ores are sometimes met 

 with in considerable masses in the primary rocks of Bohemia and 

 Saxony, and also in England, America, and the Urals. The pre- 

 liminary treatment of the ore is very simple ; for example, the sulphide, 

 MoS 2 , is roasted, and thus converted into sulphurous anhydride and 

 molybdic anhydride, MoO 3 , which is then dissolved in alkalis, generally 

 in ammonia. The ammonium molybdate is then treated with acids, 

 when the sparingly soluble molybdic acid is precipitated. Wolfram is 

 treated in a different manner. Most frequently the finely -ground ore is 

 repeatedly boiled with hydrochloric and nitric acids, and the resultant 

 solutions (of salts of manganese and iron) poured off, until the dark 

 brown mass of ore disappears, whilst the Dungstic acid remains, mixed 

 with silica, as an insoluble residue ; it is treated also with ammonia, 

 and is thus converted into soluble ammonium tungstate, which passes 

 into solution and yields tungstic acid when treated with acids. This 

 hydrate is then ignited, and leaves tungstic anhydride. The general 

 character of molybdic and tungstic anhydrides is analogous to that of 

 chromic anhydride ; they are anhydrides of a feebly acid character, 

 which easily give polyacid salts and colloid solutions. 8 bis 



8 . bli The atomic composition of the tungsten and molybdenum compounds is taken as 

 being identical with that of the compounds of sulphur and chromium, because (1) both 

 these metals give two oxides in which the amounts of oxygen per given amount of metal 

 stand in the ratio 2:3; (2) the higher oxide is of the latter kind, and, like chromio 

 and sulphuric anhydrides, it has an acid character , (3) certain of the molybdates are iso- 

 moiphous with the sulphates ; (4) the specific heat of tungsten is 0'0334, cpnsequently 

 the product of the atomic weight and specific heat is 6'15, like that of the other elements 

 it is the same with molybdenum, 96'0 x 0722 = 6'9 ; (5) tungsten forms with chlorine 

 not only compounds WC1 6 , WC1 5 , and WOC1 4) but also WO 2 C1 2 , a volatile substance the 

 analogue of chromyl chloride, Cr0 2 Cl 2 , and sulphuryl chloride, SO 2 C1 2 . Molybdenum 

 gives the chlorine compounds, MoCl 2 , MoCl 3 (?), MoCl 4 (fuses at 194, boils at 268 ; 

 according to Debray it contains MoCl 5 ), MoOCl 4 , Mo0 2 Cl 2 , and MoO 2 (OH)Cl. The 

 existence of tungsten hexachloride, WC1 6 , is an excellent proof of the fact that the type 

 SX appears in the analogues of sulphur- as in S0 3 ; (6) the vapour density accurately 

 determined for the chlorine compounds MoCl 4 , WC1 6 , WC1 5 , WOC1 4 (Roscoe) leaves no 

 doubt as to the molecular composition of the compounds of tungsten and molybdenum, 

 for the observed and calculated results entirely agree. 



Tungsten is sometimes called scheele in honour of Scheele, who discovered it in 1781 

 and molybdenum in 1778. Tungsten is also known as wolfram ; the former name was the 

 name given to it by Scheele, because he extracted it from the mineral then known as 

 tungsten and now called scheelite, CaWO 4 . The researches of Roscoe, Blomstrand and 

 others have subsequently thrown considerable light on the whole history of the compounds 

 of molybdenum and tungsten. 



The ammonium salts of tungsten and molybdic acids when ignited leave the anhy- 

 drides, which resemble each other in many respects. Tungsten anhydride, WO 3 , is a 

 yellowish substance, which only fuses at a strong heat, and has a sp. gr. of 6'8. It is 

 insoluble both in water and acid, but solutions of the alkalis, and even of the alkali car- 

 bonates, dissolve it, especially when heated, forming alkaline salts. Molybdic anhydride t 

 MoOj, is obtained by igniting the acid (hydrate) or the ammonium salt, and forms a 

 white mass which fuses at a red heat, and solidifies to a yellow crystalline mass of sp. gr. 



