NARRATIVE OF THE CRUISE. 
973 
Challenger water analyses, had the satisfaction of finding that they had all given a small 
surplus of base, amounting on an average to 86 equivalents per 10,000 equivalents of acid 
present, corresponding (if we assume the excess of base to be present as normal carbonate) 
to about O'll gramme of carbonic acid, equivalent to 0'25 gramme of carbonate of lime per 
1000 grammes of sea water analysed. While recognising the importance of this result, I 
was keenly alive to the possibility of its having been brought about by a constant positive 
error in my sum total of base determinations, and accordingly sought for an exact 
direct method for the determination of the surplus base in a given sea water.” 
That sea water has an alkaline reaction was observed early in the cruise by Mr. 
Buchanan. On the 29tli September 1873 it was first remarked, and on that day the 
alkalinity in the cold of the surface water was repeatedly determined in samples of 
500 c.c. each by means of tenth normal hydrochloric acid, using rosolic acid as an index. 
It was found that 3'5 c.c. 0THC1 was required to neutralise 500 c.c. sea water, or that 1 
litre of sea water is sufficiently alkaline to neutralise 7 c.c. of tenth normal acid, neutrality 
being indicated by rosolic acid. In other words, the alkalinity is equal to what would be 
produced by dissolving 28 mgrm. caustic soda (NaHO) in a litre of water. It was found 
that the water so neutralised reco vered its alkaline reaction on standing, and that its 
alkalinity was increased by bo il ing. 
Mr. Buchanan’s observation of the alkalinity of sea water, though original, was not 
new. It had already been observed by v. Bibra. Its true significance was not seized 
until the discovery was again made independently by Torn0e on the Norwegian expedi- 
tion. By working it out he showed that the whole of the carbonic acid in the sea waters 
experimented on by him must be taken as combined with base, and the average of his 
experiments gave for carbonic acid forming carbonates 5278 mgrm. per litre and for 
carbonic acid forming bicarbonates 43 '64 mgrm. per litre, that is, that in the average of 
the waters examined by him there were bicarbonates and neutral carbonates dissolved 
in the proportions of 43 : 9. It is evident that in these waters there was no carbonic 
acid which could be called “ free,” and the deficiency in the amount required to form 
bicarbonate goes to explain the alkaline reaction of freshly drawn sea water in the cold. 
Professor Dittmar in his Report treats the subject of the alkalinity of sea water and 
its dependance on dissolved carbonates in an elaborate and exhaustive manner. 
The average composition of ocean water salts, as the result of 77 complete analyses, 
has been given on p. 954. Commenting on these results, Professor Dittmar says d — 
“ As a general result of Forchliammer’s and my own analyses, the above numbers 
may be taken as holding approximately for any sample of ocean ivater. Of the degree 
of approximation we can form an idea by comparing my numbers for the percentages 
of chlorine, sulphuric acid, magnesia, and potash, with the corresponding entries in the 
77 reports tabulated on pages 23 to 25, and the numbers for the lime there with 
1 Phys. Chem. Chall. Exp., part i. p. 204, 1884. 
