at Electrodes to various Electrical Phenomena. 147 



tube, open at its upper end, 

 19*0 cm. high, and 3'0 cm. 

 internal diameter (see sketch). 

 One of the platinum plates was 

 suspended vertically in the 

 upper end of the tube by 

 means of a platinum wire ; 

 and the other, welded to a 

 stout platinum wire, was sup- 

 ported vertically in the lower 

 end by passing the wire 

 through a cork fixed in a hole 

 in a vulcanized indiarubber 

 bung which closed the end of 

 the tube. The two plates were 

 9*0 cm. apart. The glass tube 

 was nearly filled with the acid 

 liquid ; its upper end was sur- 

 rounded by a water-bath, the 

 water in which was heated by 

 applying a flame to a projecting arm of the bath. The bulb 

 of a thermometer was immersed in the acid liquid near the 

 upper plate ; and the wires from the plates were attached to 

 a dead-beat D'Arsonval galvanometer. The liquids were not 

 stirred during the experiments. 



With the lower plate at 14° C, and the upper one at 95° C, 

 in the dilute nitric acid, a thermoelectric current of about 

 '00004 ampere was produced. At the same temperature, in 

 the dilute sulphuric acid, the strength of current produced 

 was about '00001 ampere. The current flowed from the cold 

 plate through the liquid to the hot one in each case. As 

 platinum is a thermoelectro-positive substance, though in a 

 feeble degree, in metallic couples, these results indicate that 

 both these liquids were thermoelectro-positive, and much 

 more strongly so than platinum. 



The electromotive forces of these couples during a state 

 of balanced current were measured by means of a modified 

 form of PoggendorfFs method ; and the values found were as 

 follows :— With the plates at 14° and 95° C. in the dilute 

 nitric acid, -418 volt; in the dilute sulphuric acid, *282 volt; 

 and in a mixture of one volume of hydrochloric acid and ten 

 of water, *208 volt. 



The amounts of " surface-resistance " were also measured 

 by using a rheostat as a slide-wire bridge ; the same elec- 

 trodes, with the same amounts of immersed surface, being 

 employed as were used in the thermoelectric experiments. 



L2 



