

and Chemical Action on a Steam-Jet. 315 



In my ' Applications of Dynamics to Physics and Che- 

 mistry ' I have calculated the change in the vapour-pressure 

 of the water- vapour due to this cause (1) when the electrical 

 field is uniform. If p is the equilibrium vapour-pressure 

 when there is no electric field, 8p the increase in p due to a 

 uniform electric field of strength H, K the specific inductive 

 capacity of the medium surrounding the drop (that of the 

 drop itself being regarded as infinite), 6 the absolute tem- 

 perature, a the density of water, and R a quantity defined by 

 the equation 



p=R,6 P , 



where p is the pressure due to the water-vapour ; 



8p = 3KH^ 

 p ^iTraHO 



The greatest electric field which can exist in air at atmo- 

 spheric pressure without causing discharge is one where H is 

 about 10 2 in electrostatic measure, for water- vapour at 15° 0. 

 R0 is about 1*3 xlO 9 ; thus, 



Sp 1 . . 



j=- W roughly. 



Thus the greatest change is excessively small, and is inde- 

 pendent of the size of the drop, so that the uniform field will 

 not be able to counterbalance the effect of surface-tension, 

 since the latter varies inversely as the radius of the drop, and 

 therefore where the drop is very small must be greater than 

 the constant effect due to the electric field. 



The case is, however, very different when the electric field, 

 instead of being uniform, is due to a number of charged 

 atoms distributed throughout the volume occupied by the 

 steam. Recent experiments seem to show r (see J. J. Thom- 

 son, " Electrolysis of Steam," Proc. Roy. Soc. liii. p. 90, 

 1893) that the charges carried by the atoms of a gas are the 

 same as those associated with them in electrolytic phenomena. 

 To calculate the charge on each atom of hydrogen we require 

 to know the values of some quantities, such as the number of 

 molecules in a gramme of hydrogen, to which we are at pre- 

 sent only able to assign approximate values ; for the purpose 

 of illustration we may take Richarz's value for the charge on 

 an atom of hydrogen, viz. 12*9 x 10 -11 in electrostatic units. 



In my i Applications of Dynamics to Physics and Chemistry/ 

 I give, on page 167, the following expression for the increase 

 hp in the pressure of the aqueous vapour in equilibrium 



Y2 



