296 PRINCIPLES OF CHEMISTRY 



compounds with carbon and iron (the addition of tungsten to steel 

 renders the latter ductile and hard). 9 Molybdenum forms a grey powder,, 

 which scarcely aggregates under a most powerful heat, and has a specific 

 gravity of 8 '5 It is not acted on by the air at the ordinary tempera- 

 ture, but when ignited it is first converted into a brown, and then into a 

 blue oxide, and lastly into molybdic anhydride. Acids do not act on it 

 that is, it does not liberate hydrogen from them, not even from 

 hydrochloric acid but strong sulphuric acid disengages sulphurous 

 anhydride, forming a brown mass, containing a lower oxide of molyb- 

 denum. Alkalis in solution do not act on molybdenum, but when fused 



has a bitter, astringent taste, and does not yield gelatinous tungstio acid (hydrogel) 

 either when heated or on the addition of acida or salts. It may also be evaporated to 

 dryness; it then forms a vitreous mass of the hydrosol of tungstic acid, which adheres 

 strongly to the walls of the vessel in which it has been evaporated, and is perfectly 

 Soluble in water. It does not even lose its solubility after having been heated to 200, 

 and only becomes insoluble when heated to a red heat, when it loses about 2^ p.c. of 

 water. The dry acid, dissolved in a small quantity of water, forms a gluey mass, just 

 like gum arabic, which is one of the representatives of the hydrosols of colloidal 

 substances. The solution, containing 5 p.c of the anhydride, has a sp. gr. of T047 ; with 

 20 p.c., of 1'217; with 50 p.c., of T80; and with 80 p.c., of 8'24. The presence of a 

 polymerised trioxide in the form of hydrate, H 2 OW 5 O or H S O4WO 5 , must then be 

 recognised in the solution : this is confirmed by Sabaneeffs cryoscopic determinations 

 (1889). A similar stable solution of molybdic acid is obtained by the dialysis of a 

 mixture of a strong solution of sodium molybdate with hydrochloric acid (the precipitate 

 which is formed is re-dissolved). If MoCl 4 be precipitated by ammonia and washed with 

 water, a point is reached at which perfect solution takes place, and the molybdic acid" 

 forms a colloid solution which is precipitated by the addition of ammonia (Muthmann). 

 The addition of alkali to the solutions of the hydrosols of tungstic and molybdic acids 

 immediately results in the re-formation of the ordinary tungstates and molybdates. 

 There appears to be no doubt but that the same transformation is accomplished in the 

 passage of the ordinary tungstates into the metatungstates as takes place in the passage 

 of tungstic acid itself from an insoluble into a soluble state ; but this may be even 

 actually proved to be the case, because Scheibler obtained a solution of tungstic acid, 

 before Graham, by decomposing barium metatungstate (BaO4WO 3 ,9H 2 O) with sulphunc 

 acid. By treating this salt with sulphuric acid in the amount required for the precipi- 

 tation of the baryta, Scheibler obtained a solution of metatungstic acid which, when 

 containing 43 - 75 p.c. of acid, had a sp. gr. of T634, and with 27*61 p.c. a sp. gr. of 1*327 

 that is, specific gravities corresponding with those found by Graham. 



Pechard found that as much heat is evolved by neutralising raetatungstic acid as with 

 sulphuric acid. 



Questions connected with the metamorphoses or modifications of tungstic and 

 molybdic acids, and the polymerisation and colloidal state of substances, as well as the 

 formation of complex acids, belong to that class of problems the solution of which 

 will do much towards attaining a true comprehension of the mechanism of a number of 

 chemical reactions. I think, moreover, that questions of this kind stand in intimate con- 

 nection with the theory of the formation of solutions and alloys and other so-called inde- 

 finite compounds. 



9 Moissan (1893) studied the compounds of Mo and W formed with carbon in the 

 electrical furnace (they are extremely hard) from a mixture of the anhydrides and carbon. 

 Poleck and Griitzner obtained definite compounds FeW 2 and FeW 2 C 5 for tungsten. 

 Metallic W and MO displace Ag from its solutions but not Pb. There is reason for believing 

 "that the sp. gr. of pure molybdenum is higher than that (8'5) generally ascribed to it. 



