A few of the so called electrolytic valves are here briefly described:
The Audion Valve.—This valve was invented by De Forest in 1900 and is practically identical with the Fleming oscillation valve, the latter being illustrated in fig. 2,086.
Grisson Valve.—In this valve the cathode is a sheet of aluminum, and the anode, a sheet of lead, supported, in the original form, horizontally in a vessel containing the electrolyte, consisting of a solution of sodium carbonate. Cooling is effected by circulating water through metal tubes in the electrolyte itself.
Figs. 2,089 and 2,090.—The De Faria valve. This is an aluminum lead rectifier. The cathode is a hollow cylinder of aluminum placed concentrically in a larger cylinder of lead, and the whole immersed in electrolyte of sodium phosphate in an ebonite containing vessel. Cooling is effected by promoting automatic circulation of the electrolyte by providing the lead cylinder with holes near its extremities; the heated electrolyte then rises in the lead cylinder, passes out at the upper holes, is cooled by contact with the walls of the containing vessel, and descends outside the lead cylinder. It is claimed that this cooling action is sufficient to allow of a current density of 8 amp. per sq. dm. of aluminum.
Pawlowski Valve.—This is an electrolytic valve employing a solid electrolyte. It consists of a copper plate which has been coated with a crystalline layer of carefully prepared copper hemisulphide, prepared by melting sulphur and copper together out of contact with air. The prepared plate is placed in contact with an aluminum sheet and the combination is then formed by submitting it to an alternating pressure until sparking, which at first occurs, ceases.
Giles Electric Valve.—This consists of a combination of spark gaps and capacity used to protect electrical apparatus against damage due to atmospheric discharges and resonance surges. The spark gaps are formed between the edges of sharp rimmed discs of non-arcing metal. These discs are insulated from each other, and from the central tube, which provides a support for the apparatus and also an earth. The condenser effect is obtained by means of the annular discs and the tube; an adjustable spark gap, a high resistance, and a fuse all connected in series, complete the valve.
Fig. 2,091.—75 light Westinghouse-Cooper Hewitt mercury vapor rectifier constant current regulating transformer. View showing assembly in case.