140 Prof. W. E. Ayrton on the Electrical 



plate from the box. The connexions with the box and plate 

 wore made as before, by first electrotyping the carbon with 

 copper ami then soldering on copper wires, the junctions of 

 the carbon and copper not being in contact with the lead 

 chloride. A condenser was also made with a copper box and 

 a copper plate, the two being well coated with graphite to 

 protect them from the action of the lead chloride, and separated 

 from one another by three small pieces of glass 0*135 centi- 

 metre in thickness. 



Tests of conductivity were now made at different tempera- 

 tures with both condensers, 0*075 volt being employed with 

 the carbon and 7*5 volts with the copper condenser, or some- 

 times 2"2 volts with the latter. With the carbon condenser 

 and with the smaller electromotive force the resistance was 

 found to increase with electrification, whereas with the copper 

 condenser and with the electromotive force 2*2 volts the re- 

 sistance diminished with electrification, and with 7*5 volts this 

 diminution became much more rapid, these results being 

 observed at both high and low temperatures. In the earlier 

 experiments with this copper condenser the diminution was 

 regular, whereas later on it proceeded irregularly; but on the 

 whole it may be said that when an electromotive force not 

 exceeding If volt was employed there was an increase in 

 resistance by electrification, such as is usually experienced with 

 gutta-percha and with ordinary dielectrics, while when the 

 electromotive force exceeded this limit there was either a 

 regular or an irregular diminution of resistance by electrifi- 

 cation — the results apparently not depending much on whether 

 carbon or copper coated with graphite was used for the plates 

 of the condenser. 



As this limiting electromotive force appears to be about the 

 same as that necessary to decompose water, I think we may 

 fairly conclude that the diminution in resistance is due to a 

 decomposition of the damp (which appears to be contained in 

 the lead chloride even when careful means are taken to dry 

 it), and to the products of the decomposition acting on the 

 chloride. Fig. 5 shows four electrification-curves, AAA, 

 B B B, C C C, D D D, obtained from four successive experiments 

 with the carbon box, and corresponding with the temperatures 

 15° C, 57° C, 14° C, 61° C. respectively. Time is measured 

 parallel to X, the points and X corresponding to the 

 moment of applying the battery, and to 50 minutes after- 

 wards ; conductivity is measured parallel to O Y from the line 

 O X of zero conductivity. The curves B B B and C C C, for 

 57° C. and 61° C, are drawn on a vertical scale five times 

 smaller than that employed for A A A and C C C — the scale for 



