242 TRANSACTIONS LIVERPOOL BIOLOGICAL SOCIETY. 



to a potential of hydrogen-ion concentration of approximately 

 P H) 10~ 8 * 2 , and the neutral point to methyl-orange to a hydrogen- 

 ion potential of P H) 10~ 45 . So that the figures indicate, 

 expressed otherwise, the c.c. of N/100 acid required to produce 

 this amount of change in hydrogen-ion concentration. 



The limits are arbitrary, but they correspond closely to 

 the extreme limits of a dilute solution containing, as the factors 

 conferring its acidity or alkalinity, the carbonates or phosphates 

 of the alkalies or of alkaline salts (such as calcium or 

 magnesium). 



The turning point of coloured indicators in such solutions 

 is not a sharp line, but a band of some width. Roughly the 

 " phenol-phthalein neutral point " corresponds, in dilute 

 solutions (such as are the physiological solutions) to the 

 " bi-carbonate point " and to the "alkaline-phosphate point " 

 respectively ; while the " methyl-orange point " corresponds 

 to the " complete carbonate neutralisation point " and the 

 " acid-phosphate point " respectively. 



These points accordingly give convenient limits for 

 obtaining some quantitative measurement of that interesting 

 property which has been called the " Reactivity " or " Buffer 

 Effect " of a solution. 



It is not claimed that they mark limits of viability, for, 

 as will be seen in the next section of this paper, the green cells 

 of marine algae and other marine plants, can live and photo- 

 synthesise up to the much more highly alkaline point (or lower 

 hydrogen-ion potential point) marked by the conversion of 

 all the carbonate or carbonic-acid, into " normal " carbonate. 



However, these figures, representing the " Buffer Effect " 

 or " Reactivity," do possess a substantial value, especially for 

 the bio-chemist ; for, a solution which possesses a low value of 

 reactivity within this range will also possess a low value in the 

 longer ranges such as that up to the normal carbonate on the 

 alkaline side, or other defined limits. 



