September 26, 1918 



NATURE 



77 



it all) bj thi electrii fui nai e than b) th aid 



ol fuel, 



I in nai es ol tbii t) tons i apacit) have bei n i on- 

 structed, and this is considered b) some authorities to 

 bi the uppei limit ol economii size. One oi thi 

 di .iu bai ks at p ation of the 



refractor) lining; but this trouble will no doubt bi 

 overcome b) the production of durable refractories b) 

 electric-furnace methods. In the event of one or mon 

 of the super-powei stations proposed by the Coal Con- 

 servation Committee being erected near London, it i- 

 quite possible that the metropolis may become an im- 

 portant centre ol the steel-refining industry. 



Direct oxidation of the nitrogen in the atmosphere 

 may l>e effected by the electric arc, and several types 

 of furnace have been designed for the production of 

 nil! ic .tcid l>v this means. 



Two other chief methods of nitrogen fixation, in- 

 volving high-temperature processes, have been intro- 

 duced : the Serpek process, in which aluminium nitride 

 is first formed, and from which ammonia is obtained 

 by treatment with water; and the cyanamide process, 

 in which nitrogen is passed over heated calcium car- 

 bide, yielding the compound CaCN,, from which am- 

 monia ma\ b< obtained 1 >\ treatment with steam. In 

 each case the ammonia produced may be converted by 

 catalytic means into nitric acid. 



The pre-war consumption of carbide in this country 



was aboul 3 id tons, of which all but about 2000 tons 



was imported. The small quantity made at home 

 came from the works of the British Carbide Products, 

 Ltd., at Thornhill, where power was obtained from 

 the Yorkshire Power Co. The di mand for carbide for 

 various purposes has greatly increased during the war, 

 and the works of the company named have now been 

 removed to Clayton, near Manchester, where furnaces 

 have been installed capable of turning out 15,000 tons 

 per annum, power being taken from the Manchestei 

 Corporation. 



Whether the manufacture of carbide in Britain will 

 become a large and profitable industry depends upon 

 the success or otherwise of schemes for producing 



• heap electrical power. 



The history of carborundum furnishes one of the 

 romances of science, and. shows how a small laboratory 



• xperimenl may result in the establishment of a large 



and prosperous industry. 



The' main reaction in the production of carborundum 

 ihown by the equation SiO + 3C = SiC+ 2< 'O. 

 Carborundum is therefore chemically silicon carbide. 

 In the manufacture on the large scale a mixture of 

 sand, coke, and a quantity of common salt is placed 

 in the electric furnace round a core of granular carbon, 

 through which the current passes. The portion of the 

 mixture adjacent to the core is convi rted into carborun- 

 dum to a certain depth, beyond which a partial con- 

 version onh takes place, forming what is known as 

 nid." 



The chief sources of carborundum are the electric 

 furnaces of the Carborundum Co. at Niagara, and of 

 tin Norton Co., Chippewa, Ontario, the product of 

 the latter company being designated by the trade nun 

 " I Yvsi 



articles of carborundum an- now manufac- 

 tured in 'bis country by thi- Carborundum Co., Ltd.. 

 at Manchester, the raw material being obtained from 

 undum grindstones are now used in 

 most engineering works, and in tin small form an 

 employed largely In dentists. 



Carborundum sand, the outer zone product, is used 

 for lining brass furnaces, silicate of soda being used 

 as bond. It is also used, mixed with fireclay, as a 

 furnace lining, as a moulding sand for aluminium, 

 and for manv refractory purp< >- 



By using a smaller quantity "i carbon, the element 

 NO. 2552, VOL. I02] 



'ii. i' In in . quantities in the eli 1 



trie furnace, the 1 ug -si0 2 + 2C='Si + 2CO. 



1 ne formation ol siuo 1 urst noted in the car- 



borundum turnaci quantities may be 



'" tuction ot silicon as the 



primary substance, when di - , 1. reducing the pro- 

 portion ot carbon as shown. 1 hi Ii naent silicon thus 

 di (ami: available in bulk, wh iously it was 



more or less a laboratory curiosi . - icon does not 

 oxidise below 1200 t., and is useful as a resistance 

 material tor electricity, particular!) when strong cur- 

 H-nts are used which make the resis n. Its 



1 1 ilic resistance is about three times .,• irbon. 



I In- fusion of the mineral bauxite, an im] - form 



■ I oxide of aluminium, results in the produc .: of a 

 crystalline material inferior in hardness to carborun-, 

 dum, but superior in strength. In grinding 

 materials of high tensile strength, an abrasive ma 



is needed which will not break under the pre- 

 which must be applied, and in such cases it is found 

 that grindstones made from fused bauxite are quite 

 satisfactory, whilst carborundum wears away too 

 quickly owing to the breaking of the crystals. Fused 

 bauxite is manufactured into grindstones by the Norton 

 Co. in America under the name of "Alundum," and a 

 similar product is marketed by the Carborundum Co. 



■ it Manchester, which is termed " Aloxite." 



As an abrasive for steel, fused bauxite is unrivalled, 

 and, together with carborundum, has made possible 

 the introduction of grinding machinery which for many 

 purposes is preferable to steel cutting-tools, producing 

 a better finish in a shorter time. 



Whilst used primarily as an abrasive, fused bauxite 

 may be made into an excellent refractory, and the 

 alundum ware produced by the Norton Co. is exten- 

 sively used for the tubes of small resistance furnaces, 

 crucibles, pyrometer sheaths, etc. In making articles 

 of this kind the powdered alundum is mixed with a 

 suitable bond, and the object moulded from the mix- 

 ture and afterwards fired. The product so obtained 

 has a low coefficient of expansion, and withstands 

 sudden changes of temperature far better than porce- 

 lain, but not so well as silica. It is relatively a good 

 conductor of heat, which property fits it for -the pur- 

 poses named ; and its high melting-point — 2050 C. — 

 renders it suitable for work at temperatures which 

 would cause fused silica to devitrify. It has the 

 further advantage of being inert towards platinum 

 at high temperatures, and is, therefore, suitable for 

 platinum-wound resistances furnaces. Culinary alun- 

 dum is porous, and this property has been put to use 

 for filtration purposes in laboratories, the liquid to be 

 filtered being poured into a crucible, in the pores of 

 which the finest particles of precipitate are retained. 

 \s the alundum is unattacked b) mosl acids, solutions 

 may be filtered which would destroy filter-papers. In 

 the form of various articles alundum has now become 

 firmly established as a useful laboratory man-rial. 



Mnissan was one of thi first to notice that ordinary 

 amorphous carbon could bi converted into graphite by 

 the aid of intense heat; but the commercial produc- 

 tion of artificial graphite was due to Dr. E. G. 



\l 111 -si Ml 



I he process of manufacture consists in passing a 

 powerful 1 lectric current through coke, anthracite coal, 

 or carbon obtained from petroleum residue's, producinj 

 .1 temperature of 3700° C, which suffices to convi 

 ordinary carbon into graphite. The materials 

 placed in a loose-walled furnace, which can eas 

 dismantled to remove the products; and at tl 

 pi ratine employed most of the impurities volatilise and 

 .apours through vents in the walls. 



Artificial graphite possesses the ad ir the 



natural variety that it may bi large, 



homogeneous masses, and does quire any bind- 



