

TBANSACTIONS OF SECTION A. 639 



8. Specific Conductivity of Thin Films. 

 By Professor A. W. Reinold, F.B.S., a?ii Professor A. W. RiJCKEB, F.E.S. 



The authors have found that the specific conductivity of liquids formed of soap 

 and water, and containing a considerable proportion of glycerine and a small per- 

 centage of a metallic salt, is the same whether the liquid is in large mass or is 

 drawn out into a film not thicker than one two hundred thousandth of an inch. 

 This is not the case if the liquid be formed of soap and water only. In that case 

 the specific electrical conductivity increases as the film becomes thinner, until for 

 the thinnest films which have been observed it is about seven times greater than 

 in a large mass of the same liquid. Newton observed in very thin films (which 

 appear black) two shades corresponding to two difl'erent thicknesses. The authors 

 find that this phenomenon is only observed when the liquid consists of soap and 

 water only, and they have some reason to believe that the ratio of the thicknesses 

 corresponding to the two tints is about two to one. 



9. 8o7ne Experiments with a Buhmkorff Coil. 

 By Magnus Maclean, M.4., F.R.8.E., and Alex. Galt, B.Sc, F.B.S.E. 



The quantity of electricity induced in a secondary circuit by a ')nake in a 

 primary circuit is equal to the quantity of electricity induced in the same secondary 

 by a break in the primary. This fact was first experimentally proved by Faraday, 

 and subsequent experiments and theory corroborate the statement. If, however, 

 there is a non-metallic gap in the circuit, whether of air at ordinary pressure or 

 at much reduced pressure, as in vacuum tubes, the break impulse causes 

 a flow in one direction, and the make causes either no flow, or a much 

 less flow in the opposite direction ; because the short intense impulse 

 of the former breaks down the resistance, while the comparatively long and 

 less intense impulse of the make either does not break down the resistance at all, 

 or only does so to a much less degree, so that the effective resistance is much 

 greater in one direction than in the other. To obtain the average diflerence of 

 quantity of electricity set in motion in one direction above that in the other a 

 copper electrolytic cell was put in circuit with a vacuum tube and the secondary 

 coil of a small Ruhmkorff" coil. The solution in the cell was sulphate of copper of 

 density 1-17 with one-half per cent, of commercial sulphuric acid added. The 

 electrodes were No. 36 B.W.G. copper wire [0-0102 centimetre diameter] ; and 

 they were immersed in the solution as little as possible so as to get the best current 

 density for the deposit. The mean of seven experiments lasting from two to four 

 hours gives the average electrolytic current, calculated from the gain of the cathode 

 electrode, as one-sixth of a milliampere. The gain of the cathode electrode was, 

 in six of the seven experiments, greater than the loss of the anode electrode. 

 An electrolytic cell was also put into the primary, and the mean ratio, in three 

 experiments, between the gain of the cathode in the primary and the gain of the 

 cathode in the secondary was 6,000. The mean current in the secondary was still 

 about one-sixth of a milliampere. 



Two experiments were also tried without a vacuum tube in the secondary 

 circuit — simply the electrolytic cell. Both electrodes showed loss. Again, a long 

 thermometer tube full of sulphate of copper solution was substituted for the 

 vacuum tube. The resistance of this tube would be comparable to that of the 

 vacuum tube. [A Thomson multicellular electrometer which was put at the 

 terminals of the vacuum tube showed 165 volts. This would give the effective 

 resistance of the vacuum tube to disruptive discharges as 165^^^^=! megohm.] 

 The few experiments made with this thermometer tube in the circuit are inconclu- 

 sive, as sometimes both electrodes showed loss, and in an experiment lasting five or 

 six hours neither electrode showed either gain or loss. These last experiments are 

 to be continued, with slight modifications. It is also intended to attach a tube to 

 an exhaust pump, and try these electrolytic experiments at different pressures from 

 atmospheric pressure down to very low pressures. 



