Sept. 12, 1878] 



NATURE 



525 



ELECTRIC DISCHARGE IN GASES 

 I. 



IN a paper read some time since at the Royal 

 Society,^ Drs. Warren De La Rue and Hugo 

 W. Miiller gave the first part of an account of their 

 researches on the electric discharge in gases. This 

 part, of which we shall at present give some account, 

 consists mainly of a discription of the apparatus em- 

 ployed in this research, and of the results of their 

 experiments with gases at atmospheric pressure and 

 pressures down to 141 millimetres. They have since 

 communicated to the Royal Society a second part, which 

 treats of the discharge in highly rarefied gases (vacuum 

 tubes). 



The source of electrification used by Messrs. De La Rue 

 and Miiller was a battery of chloride of silver elements ; 

 commencing with i,cxx), the authors have from time to 

 time increased the number of cells to 11,000 joined in 

 series (11,330 volts). In spite of its containing a some- 

 what costly material, this element, when compared with 

 the many other forms of voltaic cell at present in use, 

 possesses points of advantage such as render its general 

 adoption extremely probable ; we therefore transcribe in 

 considerable detail the authors' description of it in its 

 present improved form. 



Fig. I shows a nest of twenty cells of the most 

 recent construction ; the sevei-al components of the cells 

 are given separately at the base of the stand. The glass 

 tube T is 5^ inches high, and \\ inch in diameter: it 

 has a flat bottom. The stopper c is of paraffin, and is 

 perforated with two holes, one for the zinc rod {z) to 

 pass through, the other for letting in the liquid ; the 

 latter is ultimately closed with a paraffin plug {pp). Cork 

 and india-nibber stoppers were tried and. abandoned. 

 The zinc is obtained of the Belgian Vieille Montagne 

 Company. When it is intended to keep a battery more 

 than a year in action the zincs should not be amal- 

 gamated, as the silver wires in contact with them would 

 gradually be rotted through. Platinum, which would not 

 become amalgamated, might have been substituted for 

 the silver wires ; but it would have cost 55/. extra per 

 1,000 cells. The zinc rods are 15 cm. long, 0*56 cm. in 

 diameter, and perforated at the top with a hole o'25 cm. 

 in diameter. The chloride of silver (AgCl) is cast in the 

 form of a rod on a flattened silver wire s w ; the rods 

 are 5*4 cm. long, 0762 cm. in diameter, and weigh 

 I2'97 grms. The silver wires are 20 cm. long, o" 127 cm. 

 wide, and 0*0229 cm. thick, weighing o"88 gms. each ; 

 they protrude slightly beyond the bottom of the rod of 

 chloride, as will be seen from the figure. The wires and 



Phil. Trans., clxix. pp. 55-122. 



rods were obtained from Messrs. Johnson and Matthey, 

 of Hatton Garden ; the cost, including labour of casting, 

 amounted to 2^-. per cell. 7// is a cylinder of three folds 

 of vegetable parchment ; at its lower end the folds are 

 stitched together with thread, and at the upper part they 

 are interlaced with the silver wire, and thus prevented 

 from unfurling. The object of the parchment cylinder is 

 to prevent the reduction of the chloride of silver rod, 

 which would result from its accidental contact with the 

 zinc. By giving proper bends to the silver wire before 

 making up the cell it is easy to cause the chloride rod to 

 lie vertically and press gently against the glass wall. 



The liquid used for the cells is a solution of chloride 

 of ammonium, 23 gms. to i litre of distilled water ; by 

 making use of a glass- siphon with a long arm of india- 

 rubber tubing, provided with a pinch cock, and termi- 

 nating in a glass tube drawn down to enter freely into 

 the hole in the paraffin stopper, it was found that 2,400 

 cells could be charged by one person in ten hours. 



In making up a battery the glass cells are first arranged 

 in their nests ; next the paraffin stoppers are fitted with 

 zincs ; then the chloride rods are inserted and the cell 

 closed with the stopper, the thin silver wire passing 

 between the glass and the paraffin. When these opera- 

 tions have been performed for all, the cells are joined up 

 by passing the silver wire of each cell through the hole in 

 the zinc rod of its neighbour, and securing 

 it there by pressing in a taper brass plug 

 P with a pair of pliers. Ultimately, the 

 cells having been charged with fluid, as 

 already described, and closed by the in- 

 sertion of p p, a hot iron is run round the 

 outside of the stopper and round the zinc 

 rod to secure the latter in its place, and 

 make tight the joints by the melting and 

 re-setting of a little paraffin. 



Thus set up, the battery has an elec- 

 tromotive force of about i"o3 volt and- 

 internal resistance of not more than 5 

 ohms per cell : the former remains re- 

 markably constant, but the latter increases, 

 especially in cells that are left long idle. 

 This rise in internal resistance is caused 

 by a skin of oxychloride of zinc, which 

 gradually forms on the zincs in all bat- 

 teries where the zincs are immersed in a 

 neutral chlorine compound. The battery 

 may be restored to its original resistance 

 by removing and scraping the zinc rods, but a more 

 expeditious mode is to withdraw the small paraffin 

 plug used to close the hole in the stopper through 

 which the cells are charged, and to introduce into 

 each cell, containing 50 c.c, i c.c. of pure hydrochloric 

 acid, sp. gr. i'i6, containing 31 "8 per cent. HCl gas, 

 equivalent to o"3689 gm. acid. Before introducing it into 

 the cells, as is conveniently done by means of a gra- 

 duated pipette furnished with a stop-cock, it is better to 

 dilute the acid with an equal volume of distilled Avater. 

 An effervescence takes place, and it is therefore necessary 

 to allow the tubes to remain open twenty-four hours 

 before the small paraffin plug is replaced, in order to 

 permit the hydrogen, which is generated, to escape. _ It 

 required two days for one person to perform this operation 

 on a battery of 1,200 cells. The acid dissolves 0*3295 gm. 

 of zinc or its equivalent of oxide. 



After having been in almost daily use on circuits com- 

 parable with those occurring in overland telegraphy, it 

 was found that in two batteries the amount of AgCI 

 reduced in sixteen months averaged 4*57 gms. per cell, 

 while in two other batteries which had been worked for 

 ten months the reduction amounted to 3*57 gms. per cell. 



An accident enabled the authors to give precise 

 information as to the loss in working up the reduced 

 silver ; 600 cells having been accidentally allowed to run 



