222 



Profs. W. E. Ayrton and John Perry. [Mar. 21, 



key the deflections to right and left of zero were found to be nearly 

 equal to one another. In a short time there seemed to be an increased 

 steadiness in the amount of deflection. When the platinum and mag- 

 nesium were short-circuited for some minutes, the deflection had 

 decidedly increased in amount on renewed insulation, and this oc- 

 curred after every short-circuiting. To determine the electromotive 

 force of the arrangement, strips of platinum and magnesium, scraped 

 very clean, were dipped into pure mercury which had previously been 

 washed with distilled water, and well dried. The maximum electro- 

 motive force obtained was 1"56 volts, that is about one and a half 

 times the electromotive force of a Daniell's cell, the platinum corres- 

 ponding with the copper plate in the Daniell's cell. It may be possible 

 by mechanical or other means, or by using another metal than mag- 

 nesium, to give constancy to this arrangement; and as its internal 

 resistance is extremely small the cell may be of great practical use for 

 the production of powerful currents. It may be remarked that as an 

 amalgam may be easily separated into its components by distillation, 

 such a cell by suitable arrangements can be kept in action for an 

 indefinite time. 



We have examined a circuit composed of the metals platinum, tin, 

 and lead, and the coil of a galvanometer. On raising the temperature of 

 the tin gradually we found that there was a current, and that it gradually 

 increased. Rapid changes in the current were observable at the melt- 

 ing point of the tin, and there seemed to be a small electromotive force 

 independent of thermo-electric effects. When the platinum and lead 

 strips were connected with the electrometer, the deflections were found 

 to be too small for decided conclusions to be drawn. We shall proceed, 

 when time allows us, with the investigation of metallic voltaic cells. 



On Electrolytes of Great Resistance. 



To measure the electromotive force of the voltaic cell formed by 

 plates of zinc and copper separated by paraffin wax and other elec- 

 trolytes of great resistance, and to determine the change of conduc- 

 tivity of such electrolytes with temperature, we used the apparatus 

 shown in the figure. 



J is an oil-bath which may be clamped firmly to an iron stand 

 resting on the table of such a height that D is on a level with the 

 electrode of the electrometer. The bath was heated by means of spirit- 

 lamps. No artificial means of cooling the bath were employed. B is 

 a shallow dish of copper, quite plane on the bottom inner surface, and 

 containing the electrolyte. A is a circular plate of zinc, or of copper, 

 12*8 centims. diameter, resting in the experiment in paraffin wax 

 on three small pieces of glass, 0*191 centim. thick; the metal was 

 very clean, and was quite surrounded by paraffin wax poured in in a 

 melted state. The strip C is in one piece with the plate A, both 



