ELECTROCHEMISTRY

electrolytic alkali works are now operated in all the leading manufacturing countries where the raw materials of the industry are found; and those who controlled the operation of the old le blanc process of alkali manufacture in the united kingdom found themselves in 1921 compelled, by the force of circumstances and by the changing conditions of the trade and industry, to adopt the newer method of decomposing salt. the cells now being operated industrially may be classified either as diaphragm or non-diaphragm cells. in the former class, a porous diaphragm, composed of cement, asbestos or other material unacted upon by the electrolyte or by the ions produced by the electrolysis, is employed to separate the cell into two or more compartments; and in this way the chlorine liberated at the anode is to a large extent prevented from tak- ing part in secondary reactions with the sodium hydrate or potassium hydrate formed at the cathode. : the ‘ elektron,” mhargreaves-bird, outhenin-chalandre, basel, billiter-siemens, nelson, allen-moore, gibbs, wheeler and townsend cells are all of this type, the chief ditference between them being in the construction or position of the dia- phragm, and in the arrangements made for withdrawing the sodium-hydrate solution from the cathode compartment of the cell, before it has had time to be decomposed by the electric cur- rent. the defects of all diaphragm cells are the higher voltage required per cell, and the increased costs of maintenance, due to the non-durability of the diaphragm. 3 for these reasons non-diaphragm cells have always attracted the electrochemist. many of these have been patented and tried, but only two types have survived industrial trial— electrochemistry namely (1) the castner-kellner, whiting and solvay cells, which employ a moving mercury electrode in the cathode com- partment of the cell, and thus produce an amalgam of sodium which can be removed from the cell before it 1s decomposed with water to yield the hydrate; and (2) the “ bell ” type of gravity cell, which makes use of the different specific gravities of the brine, and of the newly formed sodium or potassium hydrate solution, in order to effect a separation of the two. the aussig “ bell’ cell and the billiter-leykam cell are now the only two representatives of this class in actual operation. the attempts to use molten lead, in place of the more expensive mercury as the liquid or moving electrode, failed after trial upon an industrial scale in the united states of america. the answer to the question as to which type of cell is the best for the production of caustic soda or caustic potash, depends largely upon the relative costs of electric power and of fuel in the locality where the cell is to be operated. ; _the diaphragm cells with the highest efficiency, unfortunately, give the weakest solution of sodium hydrate at the cathode; and tn order to obtain a concentrated cathode liquor it is necessary to sac- rifice to some extent the energy efficiency of the cell. - ; the whiting, castner-kellner, and wilderman types of mercury cell all yield cathode liquors of a fairly high degree of concentration, namely, 200 to 240 grammes per litre of naoh. but for the high cost of mercury, the mercury type of cell would probably be generaily adopted for the production of caustic hydrates, for this type yields a specially pure product, both at the anode and the cathode. the billiter-siemens, billiter-leykam, townsend and nelson cells all yield a liquor containing 120 to 160 grammes per litre naoh, and therefore come next to the mercury cells, as regards the concen- tration of the caustic liquor. the gibbs and whecler cells produce a liquor containing 100 to 120 grammes per litre naoh, but as com- pensating advantages have a very low capital cost and a low main- tenance charge, due to their cylindrical shape and small size. at the present time (1925) these two types of cell are in extensive use both in great britain and in the united states of america, and it is note- worthy that the united alkali co., after exhaustive enquiries in 1920-1 adopted one of these cells (the gibbs) for the equipment of their new electrolytic alkali works at widnes. the aussig bell, griesheim, andi outhenin-chalandre cells on the other hand, yield a liquor containing only 60-80 grammes naoh (or under) per litre, and in view of the amount of fuel required to produce solid caustic from weak liquor, it is surprising that these cells have attained such wide use on the continent of europe. the war caused a considerable increase in the number and capacity of the works for the electrolytic decomposition of brine, liquid chlorine being required in very large amounts by the military authorities, for gas warfare and for sterilising water supplies. chlorates and perchlorates —the electrolytic method of man- ufacture of chlorates and perchlorates is now operated in all countries where cheap power is available, the most notable works being located at chedde in the haute savoie, and at mansboe and trollhiittan in sweden. the cells in use at chedde are constructed of cement, and are arranged in terraces so that the electrolyte can flow through them by gravity. very thin sheets of platinum foil fixed in ebonite frames are used in series as bipolar clectrodes; and the number of these in a cell, and the number of cells in a circuit, are arranged to suit the voltage of the generators. when potassium chloride is employed as the electrolyte, the chlorate can be casily separated from the unaltered chloride by crystallisation. when sodium chlorate is to be produced, a differ- ent treatment is required to obtain separation of the chloride and chlorate, since the sodium salt is much more soluble than potassium chlorate. he current efficiency, when producing either sodium or potassium chlorate can be raised, under the best conditions, to go %, and the conversion of the chloride into chlorate can be completed in one operation, perchlorates—the conditions required in order to obtain perchlorates in an electrolytic cell are: (1) insoluble electrodes; (2) a high current density at the anode; (3) the prevention of any reducing action by the hydrogen gas liberated at the cathode. this latter condition is obtained either by the use of a diaphragm, or by the employment of salts which suppress the cathodic reduction, chromates or cyanides being used for this purpose. | | , electrometallurgy under normal conditions, the conversion of the chlorate into perchlorate takes place without evolution of ozone, and shows an average current efficiency of 85%). the power required to produce one kgm. of sodium perchlorate from sodium chlorate, is about 33 kw. hours; and as the sodium salt is deliquescent, it is usually at once converted into the potassium salt by treatment with potassium chloride or sulphate. ammonium perchlorate, which is used largely in the manufacture of explosives, is prepared in a similar manner, by treating a sodium perchlorate solution, produced electrolytically, with ammonium sulphate. an alternative method of manufacturing the ammonium salt is to start with calcium chloride, and to convert this by successive stages of anodic oxidation into calcium perchlorate, which is finally decomposed by ammonium sulphate. sodium perboraie—this persalt is most easily produced by the electrolysis of solution of sodium borate. the process of manufacture employed is based on the use of a mixed electrolyte of sodium borate and of an alkaline carbonate. the latest theory of the conversion is that a percarbonate is formed first, and that this salt then reacts with the sodium borate. persulphates and ilydrogen peroxide—dersulphates are another class of highly oxidised salts which are finding wide application, especially in photography. here again the elec- trolytic method of production is the cleanest, simplest and most efficient. as a rule, the desired persalt can be produced by one simple operation in an electrolytic cell or bath, an impor- tant factor in the production of what are usually known as “ fine ’’ chemicals. when comparing the merits of chemical and electrolytic methods for producing persalts, it is necessary to note also that the cost of electric current is not the main item in the total cost of production. the method of producing persulphates in the electrolytic cell is based upon the discharge of so, ions at the anode of the cell. the conditions required io effect this discharge are the same as in the production of perchlorates, namely, (1) a low temperature, (2) a high current density with a smooth platinum anode, (3) a neuiral or acid solution. a concentrated solution of ammonium sulphate ma be employed in the anode compartment of a diaphragm type of colle with sulphuric acid of medium strength in the cathode compart- ment. platinum must be employed as anode material, but (eal can be employed for the cathodes, and these may be of much larger sur- face area than the anodes. iiydrogen peroxide-—two methods have been employed for the electrolytic production of hydrogen peroxide, the first based upon the use of persulphuric acid as an intermediate product, and the other upon the use of potassium or ammonium persul- phate. the density of the sulphuric acid in the first case should lie between 1°35 and 1°50, and the electrolysis should be carried out as rapidly as possible, with a current density of gso amp. per sq. foot. hypochlorites —charles watt, in his very remarkable master patent no. 13755 of 1851, clearly explained all the conditions which must be maintained in order to produce hypochlorites by the electrolytic decomposition of sodium or potassium chlo- ride solutions. the advance since then relates simply to the form and design of the cell used for carrying out the electrolytic method. the leading features of the cells now employed specially for hypochlorite produc- tion are, however, very similar. they possess graphite or platinum electrodes, placed so close together, that the chlorine liberated at the anode reacts at once with the alkaline hydrate formed at the cathode; and they possess also some means for promoting that rapid circulation and cooling of the electrolyte which is necessary in order to avoid the formation of chlorate. the three leading types of clectrolyser for the production of hypochlorite solutions are:—(1) the ilaas and oettel, (2) the kell- ner and (3) the mather and platt. in recent years, the electrolytic production of hypochlorites has suffered a set-back, owing to the large amount of low-priced chlorine in the liquid form which has been placed upon the market by the electrolytic alkali works. it has proved in many cases more eco- nomical for large bleaching firms to purchase this liquid chlorine in place of the usual bleaching powder, and to absorb the gas either in milk of lime, or in solutions. of sodium hydrate in their own works. in the latter case, the absorption of the gas may take place in the actual bleaching vat, and numcrous patents have been applied for, in connection with this application of liquid chlorine. oxygen and hydrogen.—cells for producing these two gases by the method of electrolytic decomposition of water, have been patented in very large numbers; and many have been operated 959 upon a commercial scale, for production of the hydrogen required for oil hardening, for ammonia synthesis (see ammonia) and for metallurgical work. the schoop, schuckert and schmidt (or ocrlikon) cells have been most widely employed in europe, while the knowles, the international oxygen company and the levin types of cell, have found most favour in great britain and in the united states of america. a remarkable expansion of the electrolytic process for hydro- gen production occurred after sabatier & senclerens’ discovery in 1897-9 that, with the aid of a suitable catalyst, the hydrogen content of liquid vegetable fats could be raised and the fat thereby converted from a liquid to a solid form. this oil harden- ing process 1s adversely affected, however, by the presence of other gases as impurities of the hydrogen, even in very small amounts, and for this reason the very pure form of hydrogen obtained by the decomposition of water has been employed on an immense scale for the operation of the oil hardening plants which have been erected since the war, in all parts of the world. it is stated on good authority that over 100,000,000 cu. ft. of hydrogen are being produced per annum for oil hardening, by an ienglish type of electrolytic cell, and the aggregate annual produc- tion of electrolytic gases in this and other countries, by all the types of cell employed, must amount therefore to an inconceivable volume. ozone.—when a high-tension electric discharge is passed through dry air, ozone is produced, and as most of the early patents covering the apparatus used have lapsed, the essential details of construction of the general type of ozoniser have now become standardised. the apparatus consists usually of an inner cylinder of sheet copper or aluminium, connected to the high-tension side of the transformer; and of an outer metal cylinder connected to the casing of the ozoniser, and main- tained at zcro potential. the two cylinders are separated by a glass tube, through which the air is passed, and the silent elec- tric discharge which produces condensation of the oxygen to ozone takes place in the annular air space between the two sheets of metal. alternating current with frequencies up to 60 cycles is employed, anil the practical limit for the e.m.f. used is found experimentally to he between 10,000 and 12,000 volts. ozonised air is employed for bleaching purposes; for the stertlisa- tion of air and food; for the acceleration of the drying and harden- ing processes in paints and varnishes, and the rapid oxidation of oils. organic products.—the use of electrolytic methods for reduc- ing and oxidising purposes is extending in the field of organic chemistry. all the best equipped works both in germany and america, where synthetic dyes and drugs and other organic chemicals are produced, are now provided with special cells for this type of work. anodic oxygen is a most energetic oxidising agent, and elec- trolytic oxidation methods are used to produce saccharine, ethane, nitrobenzoic acid and other organic products. the electrolytic preparation of salicyl aldehyde 1s also practiced. miscellaneous products—anhydrous aluminium chloride, lead arsenate, chromic acid, potassium ferricyanide and potassium permanganate, are now being produced by electrolysis. (j. b. c. bk.) electrometallurgy (sce 9.232).—this article deals with the application of the science of electrometallurgy to the various metals. aluminium.—the mineral bauxite remains the chief raw ma- terial of the aluminium industry. the increased demand, how- ever, has led to several new deposits of bauxite being discovered and worked, and the mineral has been found to be much more widely distributed than was supposed. not one of the numerous attempts to dispense with the preliminary purification and to operate the baths with raw bauxite in place of the pure alumina, in order to reduce the cost of the metal, has proved successiul. weaver (canadian patent, no. 190054 of 1919) has proposed to extract aluminium chloride from clay, with the aid of liquid chlorine. the pure aluminium chloride obtained from this source would then be fed into a bath containing molten sodium and aluminium chloride, and the process would be worked for the continuous production of aluminium and chlorine gas. an appa- 960 ratus for carrying out this electrolysis was described in u.s. patent no. 1,297,946, for 1919, and a process of this kind may eventually solve the problem of providing a cheaper raw material for the industry. the electrolytic process, by which the metal is produced at present, differs but little from that by which heroult in swit- zerland, and hallin america, first carried on the manufacture in 1889. the metal now ranks fourth in the list of non-ferrous metals, both as regards production and consumption; for only copper, lead and zinc are produced and used in larger amounts in the arts and industries. during the war, aluminium was used largely in powdered form as an ingredient of an explosive known as ““ammonal,” and for pyrotechnical work, and, either as pure metal or in the alloyed state, for the construction of air-ships, aeroplanes, motor-cars, bombs, radiators and many forms of - measuring instruments. the increased demand for aluminium and its alloys in the do- mestic arts and industries since 1920, however, has now quite compensated for the loss of the special demand for war purposes. in the electrical trade, it is employed for transmission lines, busbars, field coils and armature windings. in the motor-car industry it is employed in sheet form for the body work of. cars, for gear and crank casings, for engine cylinders, and for pistons and connecting rods. the metal is also being used to a rapidly increasing extent in the construction of vessels for the chemical, brewing, sugar refining, margarine, dyeing and soap industries, and the manufacture of domestic cooking utensils affords another large and rapidly growing outlet for the metal. aluminium can be efficiently protected against corrosion by air by a thin layer of hydrogenated cotton-seed oil. the local corrosion which often occurs, is due to minute traces of oxides and other impurities which are trapped in the metal when in the molten state before casting or rolling. aluminium carbide, which forms at a comparatively low temperature, is one of these and its presence can be avoided by preventing the access of gases containing carbon to the metal when in the molten state. artificial abrasives ——carborundum, or silicon carbide, is formed by heating a pure form of sand and carbon to a very high temperature in an electric furnace of the resistance type. this manufacture has not undergone any technical changes since 1910, but the industry has developed considerably, and now that the limitations of the material are recognised, and the attempts to apply carborundum wheels to the grincling and finishing of fine steel goods have ceased, the industry is on a very sound footing. silicon carbide is intensely hard and very brittle, and is most suitable for grinding and finishing similar materials, while arti- ficial corundum (fused alumina) has taken the place of carbo- rundum, for a variety of other grinding purposes. peters states that carborundum brick as a refractory lining for electric and other furnaces is highly resistant to the action of silicious slags, but is readily attacked by slags high in lime, lead or iron. the manufacture of corundum as an artificial abrasive is expanding, and has become one of great importance in canada. it is carried out by heating bauxite, iron and coke, in an electric arc furnace, the proportions used being as follows: calcined bauxite, 1,750 parts; coke, roo parts; iron borings, 350 parts. brass and bronze.—in 1914 there were no electric furnaces in operation for melting brass, but by the end of r919, 40 american firms were reported to be using or installing such furnaces in their brass foundries, and over 100 of these furnaces were in actual operation. by adopting electricity as the agent for heat production when melting brass, the losses occasioned by the volatilisation and oxidation of the zinc are avoided, and larger furnace units can be employed with greater uniformity in the melt, and lower labour costs. the electric furnace has therefore now almost entirely supplanted fuel-heated furnaces for brass- melting in all countries, and has been found the most economical way of melting brass, and also conducive to improvement in the health and safety of the workpeople engaged in the foundry. the following types of furnace have been used successfully for brass-melting: (1) the direct arc furnace, of which the snyder and giolitti are the chief representatives. (2) the indirect arc electrometallurgy furnace, of which the rennerfelt and the g.e.c. or detroit are the most successful examples. (3) the vertical ring induction furnace, of which the ajax-wyatt is the best known. (4) the granular resistance furnace, of which the baily is the only example. new furnaces of the induction type have been brought out re- cently by the general electric co. of u.s.a. and by the compagnie francaise de metaux, the furnace of the latter being designed for use with three-phase current. the ryan is another new resistance fur- nace, but in this case the heat is developed by means of a central graphite electrode, through which a strictly regulated current of electricity is passed. the direct and indirect arc furnaces are quite unsuitable for the rolling mills which use yellow brass as the higher temperatures they produce lead to zinc volatilisation and loss. the induction type of furnace is also unsuited for foundries where alloys high in lead are produced, or where frequent changes in the composition of the brass are necessary. the type of furnace to be chosen therefore must be determined solely by the character of the alloy or metal which is to be melted. brass founders should obtain expert and skilled advice in the selection of the furnace best suited to their needs and require- ments before embarking upon any changes in their present methods or equipment. bullion.— bullion is the technical name for alloys of the pre- cious metals silver and gold, but the name is also applied to the commercial bars or ingots of these metals which are sold for mint- ing purposes to the governments of the various countries. chemical and metallurgical methods are still employed here and there for separating or ‘‘ parting " silver and gold from one another (see cyanides), and from the baser metals with which they are often associated, but electrolytic methods of separation have been making steady progress since 1910 anda very large proportion of the silver and gold output of the world is now refined by electrolytic methods. the mocbius process, or some modification of it, is em- ee for silver refining, while the wohiwill process is used for gold yullion. the chief disadvantage of the electrolytic method is due to the large amount of gold and silver which is locked up as anodes and electrolyte in the vats used for the process. improvements therefore have been directed chiefly towards reducing the volume of the solu- tion, and the time required for the refining operation. one of the newer cells which has been devised for refining silver, is an improved form of the moebius cell, and is in operation at the ottawa mint in canada. the crude silver in this case contains from 10%, to 16% of base metal, and by means of specially designed cathodes and multiple grouping of the anodes, the current which passes through the cell is made a pulsating one. this causes the silver to be deposited on the cathodes so loosely, that it can be easily removed, and the process is made thereby a continuous one. the cells are annular, 36 in. in diameter, and are provided with a hollow centre; the electrolyte is contained in the space between the inner and outer walls of the cells. a rotating cathode is employed, and the silver is stripped continuously from the cathode as it rotates and falls into the trays, which are removed and emptied at intervals of four hours. cadmium.—this metal was produced during the war, by elec- trolysis of acid solutions of the sulphate which had been previously freed by chemical treatment from all impurities. the electrolysis was carried out in semicircular lead-lined tanks, provided with rotating disc-shaped cathodes of aluminium sheet, } in. in thickness. the output of the metal in the united states increased from 91,000 ib. in 1914 to double this amount in 1917. in germany, also, large amounts of cadmium metal were produced during the war, and were used as a substitute for tin in the manufacture of solder. the production of cadmium is still carried on in the u.s.a. at works jocated at kennett and at midvale, the raw materials in each case being obtained from the refuse and waste products or fumes of the lead and zinc smelting works. at midvale these residues con- tain 15% of cadmium, 20% of lead and 50°% of arsenic; and the solutions obtained after roasting and leaching, are treated with lime, and the filtered liquor is then passed on to the electrolytic vats for electro-deposition of the metal. calcium carbide and cyanamide.—the applications of calcium carbide for generating acetylene gas for domestic or public lighting have not expanded during the period under review, but its use in the cyanamide process, for fixation of atmospheric nitro- gen, has increased rapidly (see cyanamides; nitrogen, fixa- tion of). according to a recent estimate goo,ooo tons of calcium cyanamide are now being manufactured yearly, more than half of this total (500,000 tons) being produced in germany. the greater proportion of this output is applied directly to the soil as a fertiliser, and a small amount only is converted into the ammonium salt. the tendency in recent years has been to reduce the costs of ntanu- facture by the installation of very large furnaces, using from 5,000 to 10,000 kw. for the production of the carbide; the use of polyphase electrometallurgy current also has greatly improved the efficiency of the process of manufacture. the latest american carbide furnaces are equipped with nine electrodes, using triple three-phase current, and an output of 160 tons of carbide per 24 hours is obtained. these large furnaces are covered in and the carbon monoxide gas evolved by the opera- tion is collected and employed for preheating the raw materials or for other purposes. a continuous process for the manufacture of cyanamide from carbide is also now being operated at marignac in france, by the societe d’azote francaise, where a yield of 85 to 90% is reported, copper.—the remarkable expansion of the electrolytic method of refining copper is due to the presence ofssmall amounts of silver, gold and other precious metals, in the original copper ore. these impurities accumulate in the raw copper from the smelters, and finally appear in the slimes from the electrolytic vats. in many cases the value of these slimes covers the whole cost of the refining operation. the aggregate output of copper by all the mines in the world is approximately 1,000,000 tons p. a., of which 75 to 85° is now being refined by the electrolytic process. the greater number of refineries are located in the u.s.a., for over half the world’s out- put of copper is still produced in that country. when judged by mere tonnage capacity, or by the capital sunk in the refincries, the electrolytic copper refining industry ranks first, therefore, among the electro-metallurgical industries. the latest improvement in the conduct of the technical side of the refining operations is based upon the use of colloidal (see collords) and seno: agents for improving the character of the deposit. at the works of the boston and montana refining co., ltd., great falls, montana, gelatine is being employed in the vats for this purpose. with regard to the use of electrolytic methods for the direct ex- traction of copper from its ores, dilute sulphuric acid is employed as leaching agent for the roasted ore, and the solution of copper sulphate is purified by chemical methods before passing it into the electrolytic vats. at the extraction works operated by the cornelia copper co. the solution obtained from the lcaching opera- tion is treated with sulphur dioxide gas, in order to reduce the ferric sulphate to ferrous sulphate. the liquor is then electrolysed in the ordinary way, and the efficiency of the process depends on keeping down the percentage of ferric sulphate which is allowed to enter the rats. in the meclay extraction process now being operated in australia, a sulphide silicious ore, containing 4 °% of copper, is roasted in a special type of furnace which enables the temperature of the air and its rate of supply to be so regulated that the copper is obtained as soluble sulphate, while the iron and other impurities of the ore are converted into insoluble basic sulphates. the small amounts of tron and aluminium which accumulate in the electrolyte, after being used, are removed by means of a stream of air. graphite.—the production of artificial graphite by the electro- thermal process has become one of the most flourishing of the minor electro-metallurgical industries. the original patent has now lapsed, and there has been consequently a great expansion of the industry, which is carried on in practically every country where cheap power is available. ‘the method described by acheson in his original patent is employed and has undergone very few modifications since it was first operated on an industrial scale at niagara falls in the year 1897. artificial graphite can be employed for any of the purposes for which natural graphite has been used, but its chief application is for the construction of electrodes for electrolytic and for electric fur- nace work. its electrical conductivity is high and it can be produced in large blocks, which may be sawed, tapped, screwed or turned in the lathe, to produce electrodes of any desired shape. some graphite electrodes manufactured for electric steel furnaces have been 24 in. in diameter and 72 in. in length, and could not have been produced from natural graphite. it is also used for the manufacture of lubri- cants, paints, dry batteries, packings for engine glands, and of pre- ventives for scale in steam boilers, electric steel furnaces—during the year ro1o~25 there has been a remarkable increase in the number and capacity of the electric furnaces employed in steel works, and in steel foundries for melting and refining the higher grades of steel. in 1913 germany produced more than one-half of the world’s supplies, but before the end of the war the united states took the lead and has since retained it. the electric furnace may be employed either alone or with the bessemer or open-hearth furnace, and may be operated either with acid or basic slags. it can be employed also as an adjunct qo! of the blast furnace or of the cupola furnace, for producing grey or malleable iron and for semi-steel castings, and the smaller sized furnaces are particularly advantageous when only small quantities of castings of a particular steel or iron are required. recent improvements have been confined chiefly to the mechan- ical and electrical equipment of the furnaces, such as better-fitting doors; water-cooled arches; improvement in the electrodes and hold- ers, and automatic electrode control. as regards the holders, the tendency has been to substitute cast steel for the bronze holders which were formerly employed; and the mechanism for tilting the furnace has also been much improved, controllers of the reversing type now being used, with a motor brake which prevents over- travel of the furnace, and holds it stationary in any desired position. with regard to electrical features, the transformers are now more strongly constructed, and only two main types are in use; namely, the ieroult, operated at 110 volts, and the pittsburgh or ‘‘ lectro- molt ’’ with a voltage of nearly twice this amount. the transformers are placed as close to the furnace as possible, in order to improve the power-factor by shortening the leads. the majority of furnaces are now operated with three-phase connections, and the use of a bottom electrode is being discarded. as regards linings, the larger number of furnaces have silica brick walls; and silica brick is also generally employed for the roof, although carborundum brick has been em- ployed. another special refractory material, which has been tried with success, is fused magnesite which does not shrink and seems to have great possibilities. the majority of the are furnaces are built on the heroult prin- ciple, and have capacities of from 1 to 40 tons, and in those, both arc and resistance heating is employed. the power expenditure for melt- ing stecl for casting ranges from 500 to 600 kw. hours per ton, and for refining the metal from 700 to 1,200 kw. hours per ton. since the war, fine steel for castings is being produced. the two types of furnaces which are popular for foundry work are, the small furnace delivering from a half to one ton, and a larger one with a capacity of three to four tons. a wide field for the application of the electric furnace lies in the production of high-grade grey and white iron, since it is possible for the electric furnace to superheat the metal, both under acid and basic conditions. in great britain the chief progress to be recorded is in the manu- facture of high-grade steel. in the sheffield district the old estab- lished crucible process of steel manufacture is being gradually dis- placed by the electric process. at the works of messrs. e. allen & co., sheffield, scrap steel is being melted and refined in two stages. the preliminary melting and oxidation is carried out in a 10-ton furnace, and from this the molten metal is transferred at short in- tervals to a smaller 33-ton furnace, in which the refining operation is finished. in france the latest improvement in the heroult type of furnace has been the use of copper tubing as conductor and as carrier for the cooling water required by the electrode holders. this plan saves two-thirds of the copper, and the current leads can be brought much closer together. in the latest design of heroult furnace the super- structure, which carried the conductors and electrodes ahove the furnace, also has been dispensed with; and the electrode arms and hoklers are supported from below. the transformers and high- tension switch gear are now placed beneath the floor. improvements have also been made in the density of carbon electrodes; but on ac- count of the impossibility of producing these electrodes satisfactorily beyond a certain limit of size, heroult furnaces of 40 tons capacity cannot be exceeded. in canada a new form of heroult furnace has been applied to the melting of “‘ monel-metal ”’ at the works of the international nickel co. at huntingdon. a basic lining is used for this furnace, and the desulphurisation and deoxidation are carried out under a basic slag. the latest form of greaves-etchells furnace adopted in the u.s.a. introduces two phases of the three-phase power supply, through two or more top clectrodes, and the third phase through the fur- nace hearth. ry the use of four or more electrodes with this furnace. considerable flexibility of opcration is possible, as the top electrode and higher voltage can be employed when starting up a cold furnace, and the top and bottom electrodes when the bath is molten and the refining and superheating of the metal is in progress. furnaces of this type, with capacities of from 60 to 80 tons, are reported to be under trial by the ford motor co. at detroit, u.s.a. a multiple system of electric heating has been introduced into some american steel foundries, in order to diminish the interval be- tween one heating and the next. the method is based upon the use of two furnaces, mounted on a movable turn-table, so that either furnace can be brought under the fixed furnace cover and electrodes. where this method is adopted, the average time between successive heats is reduced to 33 min., and a load-factor of from 95 to 98% is obtained. the units employed are of 13}-ton capacity, and these provide small batches of hot metal for light castings, ready for pour- ing at regular intervals of three-quarters of an hour. by the use of this system only one charging and pouring position is required, and continuity of operation is bene obtained. the largest aecuie furnaces employed in america for steel melting and refining are the 25-ton heroult three-phase arc-type furnaces 962 erected at the south chicago works of the i[linois steel co. during the war. in 1918, these furnaces were producing steel at the rate of 16,500 tons per month, when operated under the triplex system of charging, referred to above. other types of electric furnaces used in the american steel industry are the booth-ihall, the girod, the greaves-etchells, the grenwall-dixon, the ludlum, the snyder and the von baur. ferro-alloys.—the applications of ferro-alloys in the iron and steel industry have increased enormously since 1911, and the shelield steel trade is now dependent upon these alloys for some of its most valuable products. the discovery made many years ago, that very small percentages of chromium, nickel, manganese, vanadium and other rare metals, cither separately or in combination, could produce great changes in the physical propertics of stecl, has, in fact, revolutionised modern steel manufacture, and the production of rustless or ‘‘ stainless ”’ steel (see rustless steel) was one of the most notable advances made during the war period. these special stecls are known as binary, ternary or quaternary steels, according to the number of elements (other than impurities) which are present in the finished steel, and it is the quaternary steels, containing car- bon and two other elements, which are now finding very wide applica- tior in the arts and industries. the ferro-alloys used in the manufacture of these special steels came chielly from the large electro-metallurgical works located in the french and swiss alps and dependent upon hydraulic power for their source of electricity and heat. during the war, ferro-alloys were produced in the united kingdom, at newcastle, widnes and other places, the manufacture having been scheduled as a “ key ”’ industry. since the return to peace conditions, the bulk of our sup- plies are once again being drawn from the more economically operated works abroad. the furnaces used for the production of ferro-alloys are of the resistance, not of the arc, type, and their design is based on that of the furnaces employed for the manufacture of calcium carbide. they are generally constituted with a cylindrical receptacle of ma- sonry or metal lined with a refractory metal, and equipped with one hearth-electrode and with two or more electrodes suspended above it. the chief difference between the various types is in the method of constructing the base electrode, which may be cither a plate of steel embedded in the lining used to forma hearth, or a series of steel bars arranged in fan fashion above a similar lining. in the ineller furnace, a large water-cooled graphite electrode isemployed, terminating above in a graphite hearth. the older furnaces had open tops, and the gases produced during the reduction of the ore and production of the alloy, were allowed to escape with their heat unused. modern furnaces are closed, and after recovering the dust, which may prove in certain cases to be valuable, from the gases, these latter are used for heating purposes. this improvement in the heat economy of process, together with the use of higher current densities and temperatures, has led to con- siderable economies in the opcration of the furnaces, and it is now possible to produce ferro-alloys from low-grade ores, and thus to reduce their price to the consumer. the demand for ferro-alloys containing low percentages of carbon and silicon, has led also to considerable improvements in the refining operation, and it is now possible to obtain ferro-alloys containing under -5°% of carbon. as regards the size of furnace, the tendency is towards the use of larger units, and a recent paper contributed to the jour. amer. inst. elec. engineers, described a furnace of 12,000 kv.a. capacity for the pro- duction of ferro-alloys. electric [ron smelting.—pig iron can be produced in an electric furnace, either by reduction of the iron ore with coke or charcoal by aid of electric heat, or by melting stecl scrap. the latter method is termed the “ synthetic’ production of pig iron, and has been practised chiefly in france and canada; while electric smelting is carried on only in scandinavia and italy, where very cheap electric power is available. the smelting furnaces now em- ployed are an improved type of the shaft-furnace which was first tried in rgr1 in sweden. two types of furnace are now in use for clectric smelting, namely, (a) those with a deep charge and shaft, as exemplified in furnaces of gronwall, linblad and stalhane type, and ()) furnaces with a low charge and shaft, of which the hilfenstein is the best known example. furnaces with a deep shaft are adapted for use with charcoal as re- ducing agent, while coke is the fuel used with the [ilfenstein furnace. the latest improvements in electric smelting have been the recovery of the heat from the waste gases, automatic charging, the use of continuous electrodes, and progress in transformer construction. magnesium and magnesium alloys—magnesium anc its alloys have come to the front as metals of considerable industrial value and importance in recent years, owing to the demands of the aeroplane and motor industries for a metal combining lightness, strength, toughness, and ability to resist the etfects of vibration electrometallurgy and shock. the alloys of magnesium and aluminium which con- tain from 5 to 30% of aluminium have approximately the same mechanical properties as brass, and can be employed for the manufacture of screws, nuts, wire, tubes and sheets. the hard- ness of these aluminium magnesium alloys increases with the proportion of the latter metal present in the alloy, and with 70% magnesium the hardness is equal to that of mild steel. an alloy containing 92°5 magnesium and 8°%% aluminium has been pat- ented also by a german firm, andl is stated to have a strength equal to that of gun metal, witn a specific gravity of only 1-75. in the manufacttre of the magnesium-aluminium alloys, it is of great importance that the metals should be pure. the aluminium is first melted in a graphite crucible, and a small amount of cryolite is added asa flux. the magnesium in the required amount is then in- troduced and in order to prevent loss by oxidation it is held beneath the surface of the molten aluminium by tongs, until it is melted. as regards the best contents of magnesium for alloys designed for various uses, klaudy states that a 2 to 5%) magnesium alloy is best for wire drawing; 5 to 8°, for rolling; 12 to 15 °4 for casting, and that the average strength of a cast of 10% magnesium alloy is 20,000 tb. per square inch. an alloy he recommends for acroplane construction work has the following composition: aluminium, 80 parts; mag- nesium, 12 parts; cadmium, 8 parts. as regards the methods of manufacture, magnesium is being pro- duced by the electrolysis of fused carnallite in germany, carnallite being the naturally occurring chlorides of magnesium and potassium. in america the metal is produced from pure magnesia (mgo) by a process very similar to that used for the production of aluminium. in this case, however, the magnesium oxide is added continuously to a bath composed of chlorides of potash and magnesium, and the metal is removed from the fused electrolyte as it collects at the negative electrode. details of the method used to prevent oxidation are lacking. at wolverhampton the metal is reported to be manu- factured by a two-stage process. an alloy with lead is first obtained by the electrolysis of magnesium chloride, and this lead-magnesium alloy is electrolysed in the molten state. ouarts glass.—quartz is an impure form of silicic acid (sio) and quartz glass is, therefore, a glass consisting chiefly of silicic acid; whereas ordinary glass contains silicic acid in combination with lime, soda, potash or lead. quartz glass for chemical use as compared with ordinary glass has a much higher melting point, and is not fractured by sudden changes of temperature. it is neither hygroscopic nor soluble in acids, and alkalies affect it less then ordinary glass except at the higher temperatures. it is, therefore, of great value for chemical and research work of various kinds. in the early days of its manufacture only tubes were made. the electro-thermal method of production was to embed a graphite rod in sand, and to heat this with a current of high amperage. a white opaque tube of quartz was obtained in this way, of much greater diameter than the graphite core. the opacity was due to the air entangled in the raw material, this air being imprisoned as minute air bubbles in the pasty mass, when it softened under the applica- tion of heat. a new method for producing clear quartz in various forms is now in use in the u.s.a. clean crystals of quartz are packed in a graphite crucible, and are melted under low pressure in a vacuum furnace, heated either by the oxyhydrogen blow-pipe flame or by electricity. a clear, transparent pellet of quartz, containing a few air bubbles is thus obtained. this is next placed in another graphite crucible suspended in a vertical carbon-tube electric furnace. a graphite pis- ton which just fits the crucible and loaded with a weight on top, is placed above the quartz pellet which is again brought to its fusion paint, the air bubbles in this way are caused to collapse, and the clear quartz is forced out below through openings, and is moulded as required, in the form of rods, tubes, ribbon, etc. sodinum.—this metal is now produced almost entirely for commercial and industrial purposes by the electrolysis of fused sodium hydrate, using the type of cell and process originally patented by castner. danneel has recently stated that it can be more economically produced by electrolysis of the fused chloride, and that industrial trials of this method were made before the war at chevres, near geneva, and at bozel, in the haute- savoie. the electrolyte used for this process is composed of a bath of mixed chlorides and fluorides of sodium and potassium, and the sodium chloride is fed into this bath at the same rate as that of its decomposition. tin.—electrolytic methods for stripping tin from the waste cuttings of can factories and from the old tin cans collected from towns’ refuse, were at one time operated in germany, and also electron—electrotherapy in other countries, but have now been displaced by chemical methods, depending upon the use of liquid chlorine. the electro- deposition of tin is still employed, however, in some places for refining the metal, as at perth amboy, new jersey. electrolysis is used here, to separate the tin from impurities such as antimony, arsenic, lead and bismuth, which cannot be success- fully removed by any other process. the clectrolyte used ts a fluosilicate of tin, which is prepared in the vats, and the cathodes are protected from its action by a porous vase. the electrolyte should contain 20°4 of hydrotluosilicic acid, and about 1% of sul- phuric acid; the latter is added to precipitate the lead. the current density employed is about 18 amp. per sq. ft., and the temperature of the electrolyte must be kept below 20° centigrade. zinc.—the electrolytic process for the recovery of zinc from the solutions obtained by leaching the roasted ore with dilute sulphuric acid has made remarkable progress since rgro, and the total output of electrolytic zinc is now estimated to lie between 125,000 and 150,000 tons perannum. the extraction of zinc, therefore, is now the most important electrolytic industry after those of copper and aluminium, and its growth is explained by the fact that the electrolytic method is useful for treating complex ores, which cannot be dealt with satisfactorily by the older dry methods. recent study of the conditions which yield the best result have shown the necessity for producing a high percentage of soluble zinc during the preliminary roasting of the ore, and the best temperature for attaining a high sulphatising action is found to be a dull red heat, 550° to 600° centigrade. the latest progress in the electrolytic recovery of zinc centres around the systems of purification, circulation and regeneration of the electrolyte, and one of the most recent of these improvements 1s to separate zinc ferrite from the roasted ore by passing it over a magnetic separator. two products are thus obtained, a magnetic one containing all the ferrite and some zinc oxide, and the other containing pure zinc oxide, the magnetic product is then leached with 28 % sulphuric acid and on neutralising this with the zinc oxide from the non-magnetic portion of the roasted ore, the iron is pre- cipitated as dense ferric hydroxide, which carries down with it all the arsenic, antimony and silica present in the ore. the purified solution ~ is then electrolysed with a current of 100 amp. per sq. [t., and during the electrolysis glue is added to the electrolyte, to the extent of 3 ib. per ton of zine produced. the zinc deposit obtained from this high acid process is dense and smooth, and may be detached readily from the aluminium sheet by a slight tap. electrolytic zinc works have been established in italy and in the pyrenees, one of the most recent being the works of the societe de la vieille montaigne at viviez, where 4,000 ii.p. is be- ing used, from a water power located 4o m. away. the largest plant in which electrolytic zinc is being produced is that erected in 1918 by the anaconda copper co. at great falls, mont., for recovery of the zinc from the complex zinc-lead ores of the butte district, by a sulphate leaching process. the tankhouse of this plant contains 864 vats, each 1o ft. long by 3 ft. wide by 5 ft. deep; each vat holds 28 anodes and 27 cathodes. ‘the latter are of rolled sheet aluminium, from which the deposited zinc can be stripped easily. the anodes are of chemical lead. the current for each unit of 144 cells is supplied by a rotary converter of 5,800 kw. output, 10,000 amp. at 580 v. being required to run this number of cells. at full load the current density employed is 30 amp. per sq. ft. of cathode area; but 22 to 25 amp. yields the most satisfactory deposit. electro-thermal processes of zinc extraction are practised in scan- dinavia, resistance furnaces being used in norway and arc furnaces in sweden. the resistance furnaces employed in the former country ‘are those designed by thorledsen. in this type of furnace, the roasted ore and carbon form the resistance material for the passage of the current. the zinc condensed in the first part of the receiver contains 10% of lead, further on in the receiver a deposit of 98 > of zinc is obtained, finally pure zine and zine mixed with a small amount of cadmium, the condensed metal, however, is not pure, but contains 35% of zinc powder. | the swedish process is used at trollhittan, and the works there now employ 18,000 horsepower. the mineral is first roasted, and after mixture with coke and fluorspar is submitted to the action of the electric arc. oxide of zinc and grey metal are recovered, and on submitting this to the process a second time, a metal containing 99°8 of zinc is obtained. : electrogalvanising.—the electrolytic deposition of a coating of zinc, from sulphate solutions upon iron articles is now a well- established industry in all the leading manufacturing countries. 963 bibliography.—jean escard, les fours electriques ct leurs a p- plications industrielles (1905); a.j. hale, applications of electrolysis 21 chemical industry (1918); jean escard, l’electrometallurgie du fer et de ses silliages (1920); w. rodenhauser and i. schoenawa, electric furnaces in the iron and steel industry (1920); applied chem- istry reports, society of chemical industry, vol. 7, 8,9 (1922, etc.); w.g. memillan “and w. r. cooper, electro-metallurgy, 4th ed. (1923); a. j. allmand, principles of applied electrochemistry, (1924). (-beg. kk)