528 CEESSWELL SHEARER AND DOROTHY JORDAN LLOYD, 
The true alkalinity of the “ outside water,” that is, the con- 
centration of the hydrogen ion, expressed in gram-equivalents 
per litre, has been determined by means of the colorimetric 
method of S^rensen^ by Mr. D. J. Matthews. He has kindly 
given us the following figures for the alkalinity during the 
two years covered by our work. In the latter part of 1911, 
the outside water ■” gave a distinct red colour with phenol- 
phthalein, and was consequently above 8‘0, generally 8‘15 
to 8'25. In the spring of 1912 it gave no colour with 
phenolphthalein, but tests with a-naphtholphthalein showed 
that was about 7'9, but this figure gradually increased as 
the season advanced until it was about the same as in the pre- 
vious autumn. 
By Berkefeld water we mean ordinary laboratory tank- 
water, which has been treated with animal charcoal, aerated 
and filtered through a Berkefeld filter and then stored in 
sterilised flasks. This water is Hee from bacteria and infusoria, 
which increase in such great numbers in ordinary “ outside 
water” when this has stood some time in the laboratory;, 
and it is of considerably lower alkalinity than “outside w'ater.” 
In Berkefeld water we have noticed that the seg'mentation 
of the egg is somewhat slower in the earlj" stages than it is in 
“ outside water,” and possibly this is due to the low alkalinity 
of the “ Berkefeld ” as compared with the “outside water,” 
the average alkalinity of the “ Berkefeld” water being about 
P„ = 7'40 as compared with Ph = 8T5 for “ outside water.” 
The amount of ammonia in both is roughly the same. We 
' According to Sorensen's determination the dissociation constant of 
pure water is at 18° C., and a litre of pure water at this tem- 
perature would contain 10“’“' gram-erpiivalents of hydi-ogen ions, and 
the same number of hydroxyl ions. He expresses, for convenience, the 
acidity of a solution by the syml)ol P„, which is the numerical value of 
the exponent of the concentration of the hydi-ogen ion with the sign 
changed. Thus for pure neutral water P„ = 7'07. Owing to the change 
of sign, the higher the value of Ph the lower the acidity or the greater the 
alkalinity. (See Palitzsch, “ Uber die Messung der Wasserstoflionenkon 
zentration des Meerwassers,” ‘Publ.de Circonstance No. 60. Conseil 
Permanent Internat. pour I'exploration de la Mer,’ Copenhagen. 1911). 
