360 



carbide is employed for the production of acetylene gas for illumination which it yields 

 by treatment with water reproducing calcium hydrate CaC2+2H2O = CaH2O2+C2H2. 



Another large use of calcium carbide is in the manufacture of calcium cyanamide or 

 nitrolime, which is produced when nitrogen gas is passed over calcium carbide at a high 

 temperature. This substance is used as a fertiliser for soils. The manufacture of 

 calcium carbide is carried out on a large scale at Odde in Norway, where 23,000 horse 

 power are taken from the river Tysse and used for creating electric current. Air is 

 liquefied and the nitrogen gas separated from the oxygen and used for the production of 

 nitrolime. In 1910 the total production of calcium carbide amounted to nearly 250,000 

 tons, and some 15,000 tons were used for making nitrolime. An industry of immense 

 importance which is wholly dependent on the cheap supply of electric energy is the 

 manufacture of aluminium from cryolite and bauxite. The modern process of aluminium 

 production is the result of the work of Hall in America and Heroult in France. The 

 mineral cryolite is a double fluoride of aluminium and sodium. If it is crushed and 

 mixed with powdered fluorspar (calcium fluoride) the mixture can be used and 

 in the liquid state dissolves alumina. In the manufacturing process the alumina is 

 prepared from bauxite, a crude aluminium hydrate. A mixture of cryolite, fluorspar 

 and pure alumina is placed in an iron crucible lined with graphite and melted. When 

 fluid a graphite electrode is placed in the mixture and made the anode by which an 

 electric current is passed through the liquid. The alumina is decomposed and metallic 

 aluminium is deposited at the bottom of the crucible. The success of the process de- 

 pends on the fact that molten metallic aluminium has a greater density than the fused 

 electrolyte, and hence falls to the bottom and is protected from oxidation. If the voltage 

 used per cell is not more than 5 or 6 volts the alumina alone is electrolysed and the 

 cryolite and fluorspar remain unaltered. This process is now carried out on a large 

 scale at Niagara Falls, and also at the extensive works' of the British Aluminium Com- 

 pany at Loch Leven in Scotland and at the Falls of the Foyers on Loch Ness, where 

 30,000 horse power are utilised for this purpose. By proper adjustment of the current 

 the heat created keeps the charge of salts fluid, and the pots only need aluminic hydrate 

 to be added at intervals and the pure metallic aluminium to be drawn off at the bottom. 

 At Niagara each pot has a current of 7,000 to 10,000 amperes passed through it at about 

 5 volts, or takes nearly 60 H.P., and produces 112 Ibs. of aluminium per day. This 

 process has now killed all other chemical processes and reduced the price of the metal to 

 something near is. rod. alb., with an annual output of nearly 15,000 tons. 



Another very large industry dependent on the electric furnace is the production of 

 ferro-alloys. Metallurgists have discovered the remarkable change in properties pro- 

 duced in carbon steel by the addition of a small fracture of i per cent of certain other 

 metals such as chromium, vanadium, tungsten, or nickel. Thus 0.6 per cent of vanadi- 

 um added to ordinary steel nearly doubles its tensile strength and resistance to vibra- 

 tion. If chromium is added, the chrome-vanadium steel has most valuable properties 

 in resisting shock and is largely used for motor car axles. In the manufacture of such 

 steel the small percentage of special metal is best added in the form of an iron alloy. 

 The manufacture of these ferro-alloys of iron, tungsten, nickel, vanadium, etc., is now 

 conducted in electric furnaces on an immense scale at the Girod works at Ugines in 

 France and elsewhere, also the preparation of an alloy called ferro-silicon used for im- 

 parting special qualities to cast iron and steel. 



Another electro industry of vast importance is the manufacture of nitric acid from 

 the nitrogen of the air. A few years ago Sir W. Crookes drew attention to the approach- 

 ing exhaustion of natural fertilizers such as guano and the natural nitrates, and the 

 necessity for making them from atmospheric nitrogen to maintain the world's supply of 

 wheat. This is now carried out on an immense scale in Norway and Switzerland by 

 hydroelectric power. One process, as worked out by Birkeland and Eyde and Schon- 

 herr, depends on the fact that when air is blown through an electric arc nitric oxide (NO) 

 is produced, and this can take up oxygen from the air and form nitrogen peroxide (NOz), 

 which by action on water produces nitric acid. In the Birkeland-Eyde process a power- 



