Force and Osmotic Pressure, 



401 



Hence 



re 



dV 



dF 

 dV' 



jy C 1 dE 7V 

 F = ?'el jf -rr r dV. 



The integral was evaluated graphically by the method de- 

 scribed in the following " Note on Graphical Treatment," 

 being first transformed, as there shown, into 



P=re[EC]-rr€J , EdC, 



where C = l/V is the concentration. It was assumed that for 

 a centinormal solution the osmotic pressure might be calcu- 

 lated according to Boyle's law, from the concentration and 

 the degree of dissociation as indicated by measurements of 

 conductivity ; i e. P = RTfcC. For ZnCl 2 we have t = 2 - 728, 

 for ZnS0 4 6=1*627 from Kohlrausch's data; (J being 10~ 2 

 gm.-equiv./ litre. Hence 



P= 33157 x 293 x 2-728 x 10- 2 = 0-658 atmos 



(10 6 dynes/sq.. cm.; 

 for zinc chloride, and 



P = 83157 x 293 x 1*627 x 10- 2 = 0'396 atmo 

 for zinc sulphate. The differences in pressure between centi*. 

 normal and the more concentrated solutions were then 

 measured by the planimeter, with the results shown in the 

 following table : — ■ 



Zinc Chloride. 





Osmotic Pressure 



PV. 



PV 



Gm.-equiv./litre. 



P (atmos). 



i 



001 



0-658 



658 



2412 



o-i 



6-63 



663 



27 1 



1 



637 



63-7 



32-3 



2 



1236 



61-8 



371 



3 



193 



64-3 



42 



4 



270 



67-5 





() 



446 



743 





S 



660 



825 





10 



1006 



100-6 





12 



1475 



1229 





14 



2029 



144-8 





16 



2670 



16(v9 





18 



3396 



188 5 





20 



4207 



2103 



; 



The numbers in the column PV show at first apparent 

 irregularities : but I think these are not due to errors, of 



