146 THE FITNESS OF THE ENVIRONMENT 



if the amount of acid be ten times the amount 



of salt (tTT" = 10 J, the hydrogen ion concentra- 



, tion must be 0.000003 N, and if the reverse 



be the case l-=rr = — ] the value must be 

 vBA 10/ 



0.00000003 N. 



The range of variation of concentration of 

 hydrogen ions in the usual solutions of the 

 chemical laboratory considerably surpasses 

 the limits 1.0 N and O.00000Q00000GO1 N. In 

 comparison with such enormous differences 

 those between 0.000003 N and 0.00000003 N are 



almost negligible [ : \ 



6 6 UOO 100,000,000,000,0007 



Hence ordinarily it is quite accurate enough 



to speak of any solution containing both 



free carbonic acid and a bicarbonate, when 



the disparity between the concentrations of 



the two substances is not very great, as of 



constant neutral reaction. For, obviously, 



the neutral point, which at a temperature of 



25° amounts to a concentration of hydrogen 



and hydroxyl ions 0.0000001 N, falls well 



within the narrow range of reaction of such 



solutions, being characterized by a ratio of 



carbonic acid to bicarbonate of about 1:3. 



Thus carbonic acid, like the almost equally 



weak acids sulphuretted hydrogen and phos- 



