under the Influence of the Electric Discharge. 379 



tity of electricity that involved in the Siemens-Daniell unit of 

 electromotive force. 



The quantities of heat evolved are very large; consequently 

 the electricity must suffer great loss of potential. This is also 

 seen from the following consideration. 



If in a Daniell's cell one equivalent of zinc (32*6 grammes) 

 is dissolved,- a quantity of heat amounting to 23,900 calories 

 becomes free. A current of unit strength (Siemens-Daniell) 

 would set free in one second 0*0116 milligramme of hydrogen 

 or 0*0116 x 60 x 32*6 = 22*7 milligrammes zinc in one minute. 



The whole quantity of heat produced in one minute by 



0*0227 

 such a current is therefore n * n x 23900 = 160 calories, or 



o2*b 



about one twentieth of that found above. 



The capillary tube had altogether a length of about 1 deci- 

 metre ; so that in it alone, without taking account of the heat- 

 ing at the electrodes, about 45,000 calories would be produced 

 by the unit quantity of electricity. 



The temperature of the gas in the discharge-tube at each 

 discharge may also be found from the experimental data, on 

 the assumption that the whole heat goes to raise the tem- 

 perature of the gas, and not to perforin any internal work (see 

 further on), and, further, that the discharge takes place so 

 rapidly that there is no loss of heat externally. 



If we denote by T the maximum temperature of the gas, 

 c the specific heat * of unit weight, s the specific gravity at 

 760 millims, p the pressure at which the experiment was 

 made, V the volume per unit length of the capillary tube, 

 Z the number of discharges per minute, W the water-equiva- 

 lence of the calorimeter, and t the elevation of temperature, 

 we have 



760 W ' - 



According to the data of the experiment, the value of T 

 was : — 



p 



+ 



- 



15-5 

 5-1 



1977 

 1141 



1830 

 849-2 



* The specific heat at constant pressure has been taken ; for the heating 

 of the gas in the vacuum-tube does not take place without expansion, as 

 is shown by the following experiment. If a capillary tube be interposed 

 between two wider tubes, then the whole be filled with hydrogen, and 

 by interposing sparks the quantity of electricity be so far increased that 

 the capillary tube assumes a bright-red colour, the red light continues 

 a short distance (2-3 millims.) into the wider portion of the tube, as if 

 the red luminous gas were driven into it. 



