Electromotive Force to Pressure fyt 



105 



its lower end, offering such a degree of Fig. 2. 



hindrance as to almost entirely prevent 

 the flow of the liquid, whilst allowing 

 the electric current to pass, and provided 

 with a bent glass tube at its lower end 

 to receive the lower electrode (see fig. 2). 

 In order to prevent any diminution of 

 pressure at the upper electrode an open 

 branch-tube was provided, as shown ; 

 and to obviate any increase of pressure 

 at the lower one, a minute nick in the 

 side of the lower cork allowed any of the 

 liquid which had passed through to over- 

 flow : only one drop of the liquid, how- 

 ever, was forced through by the pressure 

 in about one hour. Sufficient hindrance 

 to the passage of the liquid was obtained 

 by coating the whole of each end of the 

 diaphragm with varnish, except a minute 

 portion of the surface about 1 millim. 

 diameter. A perfectly clean diaphragm 

 was employed in each case, and it was 

 soaked in the liquid previous to use. 

 Only a single tube with zinc electrodes 

 was employed in each experiment. 



Two experiments were made, one with 

 a solution of 18' 7 grains of chlorate of 

 potassium and the other with 18*7 grains 

 of nitrate of strontium per ounce of pre- 

 boiled water, and although the circuit 

 was complete no current was produced 



by placing the tube vertical in either case (compare exps. 24 

 and 57). These results prove that the current was not 

 produced during the absence of difference of pressure. 



Influence of Difference of Pressure without Difference of 

 Altitude. 



In order to test whether difference of pressure alone was 

 sufficient to produce a current, the following arrangement was 

 employed (see fig. 3). A, pressure-tube containing mercury; 

 B, very thick tube of indiarubber ; C, glass tube with a branch 

 containing a zinc-wire electrode securely fixed in it by moans 

 of a cork and shellac; D, porous-ware diaphragm § inch Long 

 and \ inch diameter fixed in a cork ; E, a second branch-tube 

 containing the other similar electrode. The diaphragm was 

 sufficiently impervious to allow not more than one drop of the 



