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Part III. — Seventh Annual Report 



for D having risen to 1*4625. After this the value for D steadily rises 

 as the Baltic is approached, being 1-4635 and 1*464:7 at Stations XXXVI. 

 and XXXVII. in the Sound to the south of Copenhagen, and 1*4735 in the 

 surface water and 1 '4703 in the bottom water at Station XXXVIII. in the 

 Baltic. 



The density ( 4 S 0 ), as will be noticed, falls as the value for D increases. 

 At Station XXXVIII. it fell to 1006*574 at the surface and 1006*579 at 

 the bottom. At Station XXXIX. the density increased to 10*884 at the 

 surface and 1015*193 at the bottom, the values for D falling to 1*4629 

 and 1*4601 respectively. 



The determinations of alkalinity made during the cruise threw a great 

 deal of light upon the question of the influence of fresh water in raising 

 the value for D. I intend to determine the alkalinity of a number of 

 the samples in my possession, and to communicate the results of my 

 investigation on this subject at a later date. 



The merit of attracting attention to the fact of the alkalinity of 

 sea water belongs to Tornoe, the author of the Report on the Chemistry 

 of the Norwegian North Atlantic Expedition. During the cruise I deter- 

 mined the alkalinity of a number of samples by boiling 250 cc. of the 

 sea water with excess of a carefully standardised solution of hydrochloric 

 acid and titrating back with lime water. _ Aurine was used as an 

 indicator ; the end point being of course determined repeatedly. This 

 is practically Tornoe's method. The use of lime water was suggested by 

 Dittmar. As Dittmar points out, such determinations are liable to error 

 if the boiling with excess of acid is done in glass vessels, owing to the 

 action of the solution on glass. He accordingly used porcelain basins. 

 In order to make quite sure of the absence of any such error I used large 

 platinum basins. In Column XV., Table TV. the results which I obtained 

 are given calculated to miligrams of carbonic acid per litre. Under the 

 heading Da, Column XVI. Table IV., the numbers obtained by dividing 

 those in Column VII. by those in Column. XV. will be found. 



They express the relation between alkalinity and the excess of density 

 of the sea water over that of pure water under the same conditions, and 

 are in this respect analogous to those given under the heading D in 

 Column IX. When, therefore, the alkalinity increases relatively to the 

 density, the value Da decreases just as the value for D decreases when 

 the chlorine increases relatively to the density. 



The samples collected in or near the Baltic show remarkably low values 

 for Da, and moreover the value for Da decreases in those samples when 

 the value for D increases. Take the extreme case of the surface sample 

 collected at Station XXXVIII. in the Baltic. This water we may 

 suppose to have resulted from the mixing of water of high specific gravity, 

 such as the bottom water off the Naze, Station XXXIV., with the fresh 

 water flowing into the Baltic from the land. 



Now, if we compare the density ( 4 S 0 ) of the bottom water at Station 

 XXXIV. with that of the surface water at Station XXXVIIL, it will be 

 seen to have fallen from 1028*038 to 1006*574, but the alkalinity has only 

 fallen from 53*6 to 33*6. Had this bottom water from Station XXXIV. 

 been mixed with pure water until its density had fallen to that of the 

 surface water at Station XXXVIIL, then the alkalinity would have fallen 

 from 53*6 to about 12*6. Subtracting 12*6 from 33*6, the alkalinity due 

 to the fresh water is 21 mg. Thus about two-thirds of the total 

 alkalinity, or to put it in another way, two-thirds of the total bases 

 present as carbonate in this brackish water, were originally contained 

 in the fresh water, and only about one-third in the sea water. To put 

 the matter in another light, let the 21 mg. of carbonic acid per litre 



