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Rh system, but during 1910-20 there was a marked tendency toward municipal ownership of the system. The energy is purchased at the substation in bulk.

The latest statistics available for Canada are as of Jan. 1 1919 and show 795 central electric power stations in which the capital invested was $401,942,402. The total revenue from the sale of power was $53,549,133, for lighting purposes $16,952,512, and for all other purposes $36,596,621. The generating capacity at that time was 1,433,722 kva.

In Canada private operation seemed to be gradually giving way to provincial operation. The largest single system was that of the Ontario Hydro Electric Power Commission which with its latest acquisitions supplied about 1,000,000 horse-power. In 1921 this, the largest single electrical system in the world, developed under the direction of Sir Adam Beck, was being copied in other parts of Canada and was finding admirers in different parts of the United States, particularly California, where a similar system was proposed. The provincial systems were equivalent in effect to municipal control. The domestic rates were very low and as a result electricity was used quite extensively in the homes. A rate as low as one cent a K.W.-hr. was charged for electric cooking.
 * (S. B. W.)

 ELECTROCHEMISTRY (see ) and ELECTROMETALLURGY (see ). Although these subjects are essentially connected, it will be convenient here to group separately the principal headings in each case under which notable advances had been made during 1910-21.

Alkalies and Chlorine.—The electrolytic methods of producing alkalies and chlorine by the decomposition of brine made remarkable progress during the period 1911-20. Electrolytic alkali works are now being operated in all the leading manufacturing countries where the raw materials of the industry are found; and even those who control the operation of the old Le Blanc process of alkali manufacture in the United Kingdom have found themselves at last 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 as diaphragm and 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 taking part in secondary reactions with the sodium or potassium hydrate formed at the cathode.

The “Elektron,” Hargreaves-Bird, Outhenin-Chalandre, Basel, Billiter-Siemens, Nelson, Allen-Moore, Gibbs and Townsend cells are all of this type, the chief difference between them being in the construction or design of the diaphragm 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 current. The defects of all diaphragm cells are the higher voltage required per cell, and the increased costs of maintenance, due to the lack of durability on the part of the diaphragm.

For these reasons the other class—namely, non-diaphragm cells—always attracted the electro-chemist, and many of these have been patented and tried. Only two types have survived industrial trial namely, (1) the Castner-Kellner, Whiting and Solvay cells, which employ a moving mercury electrode in the cathode compartment of the cell, and thus produce an amalgam of sodium which can be removed from the cell before it is decomposed; 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 the only two representatives of this class in actual operation; the Richardson and Holland cell, which was tried on a large scale at St. Helens in the years 1896-1900, having proved a failure.

The attempts to use molten lead in place of the more expensive mercury in the liquid or moving electrode cells have also failed, after trial upon an industrial scale; the wear and tear of the cell structure, and the fire dangers with this type of cell, having caused the suspension of operation of the Hulin cell at Les Clavaux in France, and of the Acker cell at Niagara Falls in America. The works where the latter cell and process were operated was, in fact, burnt down some few years ago, and has not been rebuilt.

The World 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, not only for gas-warfare but also for sterilizing water supplies. The U.S. Government in 1918 planned and erected a large works of this type at the Edgewood Arsenal, equipping it with 3,552 cells of the Nelson (diaphragm) type in order to provide the army authorities with all the liquid chlorine they required. At the

date of the Armistice, this plant could have produced 100 tons of chlorine gas per day of 24 hours, if worked to the full.

The figures in Table I are drawn from the most reliable sources, and give a useful summary of the comparative efficiencies of the various cells as operated in 1921, and the strength of the caustic- soda solution they produce. It will be noticed that the cells with the highest current and energy efficiencies give the weakest solution of sodium hydrate at the cathode, and that in order to obtain a fairly concentrated cathode liquor, one must sacrifice to some extent the electrical efficiency of the process.

Type of Cell Cathode Efficiency % Energy Efficiency % Voltage Concentration Grammes per litre NaOH K.W. hrs. per Kgm. NaOH

Finlay 98 75 3.0 80 2.0

Billiter-Siemens 92 68 3.1 120 2.3

Vorce 97 62 3.6 — 2.5

Billiter-Leykam 95 59 3.7 140 2.6

Allen-Moore 91 59 3.5 100 2.6

Whiting 92 53 4.0 200 2.9

Hargreaves-Bird 3.7 120
 * 85

Nelson 86 53 3.8 120 2.9

Castner (rocking-cell) 92 50 4.2 200 3.1

Kellner (C. Anodes) 95 49 4.5 220 3.1

Bell-jar (Aussig) 85 49 4.0 80 3.1

Griesheim (Carbon) 70-80 45-51 3.6 60 3.0-3.4

Wilderman 97 45 5.0 220 3.4

Kellner (Pt. Anodes) 97 45 5.0 220 3.4

Townsend 94 45 4.8 160 3.4

Griesheim (Magnetite) 70-80 40-46 4.0 60 3.3-3.8

Outhenin-Chalandre 66 41 3.7 80 3.7

Theoretical figures 100 100 2.3 — 1.54


 * This cell produces Na2CO3—not NaOH.

To produce one ton of solid caustic soda from a solution containing only 80 grammes per litre of NaOH (the strength produced by the Finlay cell) means the evaporation of over 12 tons of water; whereas with a cathode liquor containing 240 grammes NaOH per litre (the strength produced by the mercury cell processes), only one-half this weight of water will have to be evaporated to obtain the solid product, and the fuel consumption will thus be reduced 50%.

The answer to the question which cell is the best for the production of solid caustic soda or potash depends, therefore, largely upon the relative costs of electric power and of solid fuel in the locality where the cell is to be operated. The Whiting, Castner-Kellner, and Wilderman mercury cells, as shown by the table, all yield cathode liquors of fairly high concentration—200 to 240 grammes NaOH per litre. If the cost of mercury were not so high, they would be generally adopted for the production of caustic hydrates and chlorine, in spite of their rather low energy efficiencies, since they also yield a specially pure product at both the anode and cathode.

Of the diaphragm types of cell, the Billiter-Siemens, Billiter-Leykam, Townsend and Nelson cells all yield a liquor containing 120-160 grammes NaOH per litre, and, therefore, come next to the mercury cells. No figures for the concentration of caustic liquor or the efficiency of the Gibbs cell are available.

The Aussig bell, Griesheim, and 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 such weak liquor, it is surprising that these cells have attained so wide a use on the continent of Europe.

Chlorates, Perchlorates and Persalts generally.—The electrolytic method of manufacture of chlorates and perchlorates of potash and soda was in 1921 being worked in all countries where cheap electric power was available, the most notable works being that of Messrs. Corbin & Cie, at Chedde, in the Haute Savoie department of France, and at Trollhattan in Sweden. The cells used at Chedde are constructed of cement, and are arranged in terraces so that the electrolyte flows through them by gravity. Very thin sheets of platinum-foil fixed in ebonite frames act as bipolar electrodes in series, the number of electrodes per cell and of cells in a circuit being arranged to suit the voltage of the generators. The electrolyte used is a 25 to 30% solution of KCl or NaCl; a current density of 100 to 200 amperes per sq. ft. of anode surface is employed. This leads to a high E.M.F.