Dielectric Constant of Liquid Oxygen and Liquid Air. 359 



each fragment being about 3 mm. square and 1 mm. thick. Four 

 of these fragments were affixed to each metal plate with a touch 

 of shellac at the four corners and one fixed in the middle. The 

 seventeen plates were then piled one on the other, the glass frag- 

 ments acting as separators, and the alternate plates were connected 

 together by wires soldered to each series. A metal clamp kept all 

 the plates in position. The condenser so formed consisted of seven- 

 teen plates, eight being the positive, and nine the negative surfaces. 

 The glass distance pieces had a total surface of very nearly 1 per 

 cent, of the total opposed surface of the plates. The condenser so 

 formed had a capacity of O'OOIOSI of a microfarad when gaseous air 

 at 15 C. and normal pressure formed the dielectric. 



If such a condenser having a capacity C' is charged to a potential 

 ~V and then discharged n times in succession into a larger reservoir 

 condenser of capacity C, it is easy to show that at the end of the 

 n successive charges the quantity Q contained in the large condenser 

 is given by the series 



Q = C'V(m-h 



C 



where 



C+C' 



Hence we have Q = C'V -- -(l-m). 



1 m 



The capacity C' of the small aluminium condenser may be con- 

 sidered to be made up of two parts ; a part which is changed when 

 liquid oxygen is substituted for gaseous oxygen or air on immersing 

 the condenser, and which thereby becomes increased. If K is the 

 dielectric constant of liquid oxygen, referred to that of gaseous 

 oxygen at 182 C. as unity; and if c. is the capacity of this variable 

 part of the condenser when the dielectric is gaseous oxygen, then 

 Kc is its capacity when liquid oxygen is substituted for the gaseous 

 oxygen at the same temperature. 



In the next place there is a small part of the whole capacity due to 

 the glass separators. These, as a whole, have a surface very nearly 

 equal to 1 per cent, of the whole surface of the metal plates, and a 

 dielectric constant, as shown below, when cooled to 182 C., of 5'0. 

 Hence it follows that that part of the whole capacity of the con- 

 denser which is due to the glass separators, may be represented very 

 nearly by 5c/100. 



This part of the capacity remains practically constant whether the 

 condenser is lifted out of the liquid oxygen into the cold gaseous 

 oxygen lying above it, and which is at nearly the same temperature, 

 or put into it, as long as the condenser is very nearly at the same 

 temperature in the two conditions. 



VOL. LX. 2 E 



