354 Prof. Helmholtz on Galvanic Currents 



according to "Wullner's experiments the diminution of the 

 vapour-pressure is to the amount of salt dissolved in the con- 

 stant quantity of water directly, and therefore to our q in- 

 versely proportional. If we use p , hitherto left undefined, 

 to denote the vapour-pressure of pure water at the tempera- 

 ture of the experiment, we may put 



Po-P=~> • ." . ■ (4) 



where b denotes a constant depending on the kind of the salt. 

 Consequently 



*p Jpk p°-p 



In intervals in which (1— n) has a constant value this would 

 become 



Wf^ • • (*•) 



=Kl-)f log(|) (40 



The quantity -^ — , here occurring, has at all events a positive 



value. If we suppose Mariotte's law valid for the inconsider- 

 able densities possessed by the aqueous vapour at the tempe- 

 rature of th;e apartment, and if V denotes the volume of the 

 mass-unit of the vapour under the pressure p, then (as noted 

 above in equation 1 c) is 



W==pV+l p.dv. 



According to Mariotte's law, 



V=Jl2L, 

 P 



<rr=-Y 1 pJte, 



P2 



\ T = PiVi{ 



ypl 



= PiVi-f.l+.lo« £ 



Pi 



|^ = &^=V (4 D) 



op p 



as an approximately correct value. 



