SEA-FISHERIES LABORATORY. 259 



The figure obtained at the point of maximum alkalinity 

 in the above experiment bears an interesting relationship to 

 the figure for the total alkalinity of sea-water, as shown by the 

 titrations to methyl-orange in the first table of the preceding 

 section of the paper. Since the turning point in colour of 

 methyl-orange lies above the hydrogen-ion concentration of 

 carbonate mixtures, it gives the total content of the sea- water 

 in all bases, including magnesium and calcium oxides, and the 

 value for such bases lies between 24 and 25 c.c. of centi-normal 

 acid for 100 c.c. of sea-water. Now the maximum value of 

 the alkalinity at which the algae cease to photo-synthesise, 

 and die, corresponds to 12-3 c.c. of centi-normal acid or exactly 

 one half of the total alkaline bases. The algal cells behave 

 like a sensitive colour-indicator and cease to functionate 

 precisely at the point where all the bi-carbonates have been 

 converted into normal carbonate. Up to this point, they have, 

 in presence of light actively converted carbon-dioxide into 

 organic carbon compounds and have flourished ; at this point 

 the gradient of alkalinity begins more rapidly to rise and they 

 are killed off. 



Experiment 2. At 3 p.m. on November 17th, 1912, a 

 wide-mouthed bottle holding approximately two litres was 

 filled with sea- water at the Life-boat Slip, about three grams 

 moist weight of Viva enter oi&es was added, and the bottle, 

 stoppered, was exposed to the daylight on the wall of the Fish- 

 spawning pond. A sample of the water was titrated at 10.45 

 a.m. on November 18th, and required 2-4 c.c. of centi-normal 

 acid to neutralise to phenol-phthalein, the neutralisation 

 figure of the " Bay " water being at the same date 0-75 c.c. 

 Thus, in a winter day when the exposure to daylight could not 

 have exceeded four hours of diffuse daylight, the photo- 

 synthetic activity had brought the alkalinity of this confined 

 volume of sea-water from the mid-winter to the Bpring level. 

 Titrated again al 1 p.m. i he alkalinity had increased to 5*9 c.c. ; 



