Force and Osmotic Pressure. 399 



inflexion and then bend quite sharply upwards, indicating 

 that the effect of departure from the gaseous laws greatly 

 prevails over that of incomplete dissociation. Thus the 

 values calculated for the range decinormal (\^ = 4) to normal 

 (\jr = '6) and normal to ten times normal (ijr = 2) on the 

 assumption of Boyle's law are 59 and 34 millivolts respect- 

 ively : the observed values are 75 and 102. 



Instead of any distinguishable point of inflexion, the curve 

 shows a long portion that is practicaily straight. In this 

 region, then, the osmotic pressure may be calculated very 

 simplj*. For then we may put 



E = — aT/r + 6= — alog l0 V + b, 

 whence 



dE dE a 



— <2, 



d-yjr dV V log, 10 ' 



But from (3), for a cell without migration, 



reE=jVdP, 



whence <£E _ V ^P 



r€ dV" dV> 



and dV a 



= — re 



dV V* log, 10 



giving 



F=re vTogao + const • - W 



The constant term is small, since the straight part of the 

 curve extends into regions where the deviation from Boyle's 

 law is negligible. It follows, therefore, that we may put 



approximately P = g-e- ^ and regard the combined 



effect of varying dissociation and the finite concentration of 

 the solution as simulating the behaviour of an ideal gas. 

 From the value 0*0747 volt for -v|r = 4 to ^r='d we o-et 



rea _ 193080 x 0747 „,_, . _ 

 k^lO 2-3026" - = 6264 J° ules - 



Now for an undissociated solution obeying Boyle's law we 

 should have at 20° 



PY= RT = 8-316 x 293 = 2437 joules ; 



the ratio is 62(54 



2437 - ti6 - 



