266 



Sorensen unit (pH), which is defined as the logarithm of the reciprocal of the 

 hydrogen-ion concentration; 



1 

 pH = log 



[H+] 



A neutral solution (i. e., a solution in which hydrogen-ions and hydroxyl-ions are 

 present in exactly equal concentrations) has a Sorensen value of pH 7. A solution in 

 which the pH value is below 7 is acid in its reaction ; above pH 7 the reaction is alka- 

 line. It should be noted that an increase in the pH value means a decrease in the con- 

 centration of hydrogen-ions, since the expression chosen is the logarithm of the 

 reciprocal of the hydrogen-ion concentration. 



Sea water is normally slightly alkaline in reaction (say, between pH 7.5 and 

 pH 8.5), due to the presence and "buffer" effect of the carbonates and bicarbonates 

 of calcium and magnesium. It is rendered less alkaline and possibly even slightly 

 acid in the presence of large amounts of carbon dioxide. Any considerable change 

 in the hydrogen-ion concentration of the water is likely to be deleterious or even 

 fatal to marine organisms, either directly, or indirectly through associated changes 

 in the physico-chemical complex of the environment. 



As nothing was known regarding the dissolved gases and hydrogen-ion concen- 

 tration of the waters of San Francisco Bay, and their possible influence on the breeding 

 and distribution of Teredo and its allies, it was considered desirable to make some 

 study of these conditions at different localities within the bay. In the summer of 

 1923 such an investigation was accordingly undertaken. The localities selected were 

 Crockett, Dumbarton, the Oakland Mole, the San Francisco Ferry Building, and 

 the Fort Scott Mine Dock (near Fort Point). Surface and bottom water samples 

 were taken at approximately hourly intervals through a twenty-hour (minimum) 

 period at each station, except at Dumbarton, where difficulty of access and inade- 

 quate facilities made it impossible to carry out the full series of observations. This 

 program was repeated for a total of three times at each locality. The factors studied 

 were salinity, temperature, dissolved oxygen, dissolved hydrogen sulfide, and hydro- 

 gen-ion concentration. 



The results of this survey are shown in the accompanying graphs (Figs. 101-105), 

 which are largely self-explanatory. A detailed analysis of the data in their broader 

 biological bearing has been given elsewhere (Miller, Ramage and Lazier, Univ. Calif. 

 Publ. Zoology, 1927). A brief summary may be given of the facts bearing on the 

 present discussion. 



At all localities the water was found to be more than four-fifths saturated with 

 oxygen. Occasional instances of saturation or supersaturation were found, such 

 conditions being the immediate effect of rapid photosynthesis by marine vegetation 

 on warm, sunny days. During the period of the investigation (about three weeks) 

 there was a progressi\'e increase in the per cent of saturation with dissolved oxygen 

 from week to week, which was correlated with a progressive increase in temperature 

 and number of hours of sunshine. 



The amount of dissolved hydrogen sulfide was usually very small, the maximum 

 value encountered being 0.42 c.c. per liter, at Crockett. The average for the entire 

 bay was only 0.13 c.c. per liter. 



The Sorensen \'alues were found to be surprisingly uniform throughout the bay, 

 the average ranging from pH 7.68 at Crockett to pH 7.95 at Fort Point. The lowest 

 value encountered, excluding certain samples taken at the mouth of a sewer, was 



