INFLUENCE OF HYDROGEN ION CONCENTRATION. 305 



vision was made for excluding the CO 2 of the atmosphere because 

 the concentration in equilibrium with the atmosphere after aera- 

 tion is, so far as our experiments are concerned, negligibly small. 

 N/4O NaOH was used for restoring this acid sea water to the 

 desired H-ion concentration, using colorimetric standards with a 

 salt content equivalent to that of sea water prepared as recom- 

 mended by Clark (2) and McClendon, (3). NaH 2 PO 4 was added 

 to the acidified sea water to give it greater buffering capacity in 

 the neighborhood of neutrality, a role normally played by 

 NaHCO 3 . A sufficient quantity of acid sea water was made fresh 

 for each day's use, and the individual solutions were prepared 

 immediately before using. 



CO 2 -free sea water prepared in this manner was used between 

 pH 4.5 and 8.0. In solutions more alkaline than pH 8.0 basic 

 phosphates are thrown out, so solutions more alkaline than sea 

 water were prepared by adding N/io NaOH to natural sea 

 water. In this case the carbonates do not interfere because the 

 CO 2 tension is negligibly small. At pH 10.2 Mg (OH) 2 begins 

 to precipitate; the amount of alkali required to complete this pre- 

 cipitation is many times the amount required to bring sea water 

 from its normal reaction to 10.2. If the precipitation of 

 Mg(OH) 2 were completed, the resulting solution would be physi- 

 ologically unbalanced. It is, therefore, impossible to go beyond 

 this point on the alkaline side. Consequently our observations are 

 limited to the range pH 4.5 to 10.2, which embraces all the physi- 

 ological variations with which we are concerned. 



The addition of HC1 and NaOH dilutes the salt content of the 

 sea water slightly but we have no reason to believe that this slight 

 degree of hypotonicity has introduced any serious complication 

 into our results. Nearly all experiments reported in this paper 

 were performed at approximately 20 C. Early in the season it 

 was necessary to bring the sea water to this temperature, but 

 later it was. easily maintained with a slight regulation of the tem- 

 perature of the laboratory. 



THE VIABILITY OF Arbacia AND Asterias EGGS. 



Asterias eggs were left in sea water until the maturation 

 process was practically completed, during which time they were 



