402 E. .1. ALLEN AND K. W. NELSON. 



Except in the cases where the alkalinity was lowered by 

 the addition of HCl, tlie results obtained from this series 

 were not up to expectation. Nevertheless the majority showed 

 a distinct improvement from increased '^alkalinity," and in 

 c, where the alkalinity had been raised 17*5 mgrm. OH 

 °/qq, this improvement was very marked. 



Another point illustrated by cultural experiment is that in 

 two samples of animal-charcoal water, one with " outside " and 

 the other with " tank-water " as a basis, the amount of growth 

 in the latter considerably exceeded that in the former, and at 

 the same time it was found that, with the tank-water, the 

 alkalinity had not been reduced to the same extent as in the 

 case of the outside water. 



How far apparently anomalous results, Avhich have so 

 frequently occuired in our experimental work, could be 

 explained by unforeseen changes in " alkalinity," can only be 

 answered by future research. 



Salinity. — The salinity (or amount of salts dissolved in 

 1000 grm. sea-water) of the outside water used in these experi- 

 ments only varied between sm.all limits, 8 = 34*5 to 35'5 

 °/qq. The salinity of "tank-water" is also fairly constant, 

 the average being about S = o4"9'^/q^; water is only pumped 

 up into the reservoirs at high Avater, spring tides, and unless 

 the salinity on analysis is Avell above S = 34*5 °/^^ no water 

 is taken. Experiments to show what effect salinity pure and 

 simple had on the growth of diatoms were undertaken. 

 Samples of sea-water of vai-ious salinities were prepared by 

 diluting down "outside water" with double distilled water, 

 and b}^ concentrating "outside water" by slow evaporation. 

 Two litres of "outside w^ater," S = 34'9, were evaporated 

 down to the bulk of one litre, giving a 50 °/q^ concentra- 

 tion. Miquel solutions 4 c.c. A, 2 c.c. B, were now added, 

 and the solution was divided into ten culture vessels, 20 

 c.c. in each. Double distilled water was added, 2 c.c. to 

 the first, 4 c.c. to the second, 20 c.c. to the last, so that a 

 series of media were obtained, varving' in salinitv from 



^ i. e. from every 100 c.c. sea-water 50 c.c. H^O had been subtracted. 



