SEA-FISHERIES LABORATORY. 237 



be obtained by taking the algebraic differences in the titration 

 figures to phenol-phthalein, and to methyl-orange, or di-methyl- 

 amido-azo-benzol. 



When a solution containing acid-salts of carbonates or 

 phosphates, or amphoteric electrolytes, such as proteins, has 

 acid or alkali added to it there is a middle zone throughout 

 which the hydrogen and hydroxy 1-ionic concentrations vary very 

 slowly, and outside this on either side there is abrupt rise and 

 fall. By choosing two coloured indicators, one near each end 

 of the range of such indicators, the breadth of this zone, or in 

 other words, the " Buffer Effect " or " Reactivity," can be 

 measured with fair accuracy. This is the figure which is 

 determined by our titrations. 



Another important effect which is given by measuring the 

 variations in titration to a given indicator (suitably chosen so 

 as to be sensitive to the varying factor) is the amount of 

 variation in a metabolic product such as carbon- dioxide from 

 one time or condition to another. Such an activity cannot be 

 followed by determining hydrogen-ion concentration alone, 

 although it is undoubtedly interesting to observe (as has been 

 done below) the variation in the hydrogen-ion concentration 

 corresponding to a given change in carbonic-acid concentration, 

 arising from photo-synthesis or respiration. 



But in a solution such as blood-serum or sea- water quite an 

 appreciable variation in titration to phenol-phthalein due to 

 change in concentration of dissolved carbon-dioxide may occur, 

 with scarcely a detectable change in hydrogen-ion concentration. 

 A ten-thousandth normal solution of a caustic alkali is 

 much more alkaline than blood serum or sea-water, but one 

 c.c. of centi-normal acid added to 100 c.c. of this caustic alkali 

 solution already suffices to remove the difference and makes 

 the solution neutral, while such an addition scarcely appreciably 

 affects the reaction of the serum or sea-water. 



This important effect was pointed out by Moore, Roaf and 



