CHROMIUM. MOLYBDENUM, TUNGSTEN, URANIUM, ETC 289 



reduction 8 of oxide of chromium and its corresponding compounds 

 gives metallic chromium. Deville obtained it /-(probably containing 

 carbon) by reducing chromic oxide with carbon,- at a temperature near 

 the melting point of platinum, about} 1750, but the metal itself does 

 not fuse at this temperature. Chromium has a steel-grey colour and is 

 very hard (sp. gr. 5-9), takes a good polish, and dissolves in hydro- 

 chloric acid, but cold dilute sulphuric and nitric acids have no action, 

 upon it. Bunsen obtained metallic chromium by decomposing a solution 

 of chromic chloride, Cr. 2 Cl 6 , by a galvanic current, as scales of a grey 

 colour (sp, gr. 7'3). Wb'hler obtained crystalline chromium by igniting 

 a mixture of the anhydrous chromic chloride Cr 2 Cl c (see Note 7 bis) 

 with finely-divided zinc, and sodium and potassium chlorides, at the 

 boiling-point of zinc. When the resultant mass has cooled the zinc may 



CrX 2 and SnXj, whilst at high temperatures, on the contrary, CrX 2 reduces the metal 

 from its salts SnX 2 . The -reaction, therefore, belongs to the class of reversible reac- 

 tions (Beketoff). 



Poulenc 'obtained' anhydrous CrP 3 (sp. gr. 8'78) and CrF 2 (sp. gr. 4-11) by the 

 action of gaseous HF upon CrCl 2 . A solution of fluoride of chromium is employed as & 

 mordant in dyeing. Recoura (1890) obtained green and violet varieties of Cr 2 Br 6 ,6H 2 O. 

 The green variety can only be kept in the presence of en excess of HBr In the solution , 

 if alone its solution easily passes into the violet variety with evolution of heat. 



8 The reduction of metallic chromium proceeds with comparative ease in aqueous 

 solutions. Thus the action of sodium amalgams upon a strong solution of Cr 2 Cl 6 gives 

 (first CrCl 2 ) an amalgam of chromium from which the mercury may be easily driven off 

 by heating (in hydrogen to avoid oxidation), and there remains a spongy mass of easily 

 oxidizablo chromium. Plaset (1891), by passing an electric current through a solution of 

 chrome alum mixed with a small amount of H 2 SO 4 and K 2 SO 4 , obtained hard scales of 

 chromium of a bluish-white colour possessing great hardness and stability (under the 

 action of water, air, and acids). Glatzel (1890) reduced a mixture of 2KC1 + Cr 2 Cl B by 

 heating it to redness with shavings of magnesium. The metallic chromium thus 

 obtained has the appearance of a fine light-grey powder which is seen to be crystalline 

 tinder the microscope ; its sp. gr. at 16 J is 6*7284. It fuses (with anhydrous borax) only at 

 the highest temperatures, and after fusion presents a silver- white fracture. The strongest 

 magnet has no action upon it. 



Moissan (1893) obtained chromium by reducing the oxide Cr.jO 3 with carbon in the 

 electrical furnace (Chapter VIII., Note 17) in 9-10 minutes with a current of 850 amperes and 

 60 volts. The mixture of oxide and carbon gives a bright ingot weighing 100-110 grams. 

 A current of 100 amperes and^ 50 volts completes the experiment upon a smaller quantity 

 of material in 15 minutes ; a current of 30 amperes and 50 volts gave an ingot of 10 grama 

 in 80-40 minutes. The resultant carbon alloy is more or less rich in chromium 

 (from 87-37-91-7 p.c.). To obtain the metal free from carbon, the alloy is broken into 

 large lumps, mixed with oxide of chromium, put into a crucible and covered with a 

 layer of oxide. This mixture is then heated in the electric furnace and the pure metal 

 is obtained. This reduction can also be carried on with chrome iron ore FeOCr 2 O 5 

 which occurs in nature. In this case a homogeneous alloy of iron and chromium 

 is obtained If this alloy be thrown in lumps into molten nitre, it forms insoluble 

 sesquioxide of iron and a soluble alkaline chromate. This alloy oj iron and 

 chromium dissolved in molten steel (chrome steel) renders it hard and tough, so that 

 Such eteel has many valuable applications. The alloy, containing about 3 p.c. Cr and 

 about 1-3 p.c. carbon, iseven harder than the ordinary kinds of tempered steel and has a 

 fine granular fracture. The usual mode of preparing the ferrochromes for adding to 

 iteel is by fusing powdered chrome iron ore under fluxes in a graphite crucible. 



