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trodes is made the positive, and the large one the negative. If this 

 electrolytic cell is connected in series with the primary circuit of the 

 induction coil (the condenser being cut out) and supplied with an elec- 

 tromotive force from forty to eighty volts, an electrolytic action takes 

 place which interrupts the current periodically,* An enormous num- 

 ber of interruptions can, by suitable adjustment, be produced per 

 second, and the appearance of a discharge from the secondary terminals 

 of the coil, while using the Wehnelt break, more resembles an alternate 

 current arc than the usual disruptive spark. 



At the time when the Wehnelt break was first introduced, great 

 interest was excited in it, and the technical journals in 1899 were full 

 of discussions as to the theory of its operation.! The general facts 

 concerning the Wehnelt break are that the electrolyte must be dilute 

 sulphuric acid in the proportion of one of acid to five or ten of water. 

 The large lead plate must be the cathode or negative pole, and the 

 anode or positive pole must be a platinum wire, about a millimeter 

 in diameter, and projecting one or two millimeters from the pointed 

 end of a porcelain, glass or other acid-proof insulating tube. The 

 aperture through which the platinum wire works must be so tight that 

 acid can not enter, yet it is desirable that the platinum wire should 

 be capable of being projected more or less from the aperture by means 

 of an adjusting screw. The glass vessel which contains these two 

 electrodes should be of considerable size, holding say a quart of fluid, 

 and it is better to include this vessel in a larger one in which water can 

 be placed to cool the electrolyte, as the latter gets very warm when the 

 break is used continuously. If such an electrolytic cell has a con- 

 tinuous electromotive force applied to it tending to force a current 

 through the electrolyte from the platinum wire to the lead plate, we 

 can distinguish three stages in its operation, which are determined by 

 the electromotive force and the inductance in the circuit. First, if the 

 electromotive force is below sixteen or twenty volts, then ordinary and 

 silent electrolysis of the liquid proceeds, bubbles of oxygen being 

 liberated from the platinum wire and hydrogen set free against the 

 lead plate. If the electromotive force is raised above twenty-five volts, 

 then if there is no inductance in the circuit, the continuous flow of cur- 

 rent proceeds, but if the circuit of the electrolyte possesses a certain 



* See Dr. Wehnelt's article in the Elektrotechnische Zeitschrift, January, 

 1899. 



fSee Electrician, Vol. XLII., 1899, pp. 721, 728, 731, 732 and 841. Com- 

 munications from Mr. Campbell Swinton, Professor S. P. Thompson, Dr. 

 Marehant, the author and others. Also page 864, same volume, for a leader 

 on the subject. Also page 870, letters by M. Blondel and Professor E. Thom- 

 son. See also Electrician, Vol. XLIII., p. 5, 1899, extracts from a paper by 

 P. Barry; Comptes Rendus, April, 1899. See also The Electrical Eevieic, Vol. 

 XLIV., p. 235, 1899, February 17. 



