104 
THE VOYAGE OF H.M.S. CHALLENGER. 
In tin* Vntaretie Ocean, where such water was met with occasionally, though very 
Ugly, the carbonic acid was always present in marked excess. The green colour of 
shoal-water is generally attributed to the influence of solid matter, which may also tend 
;o r> tain carbonic acid, as we know is the case with dissolved saline matter” (Buchanan, 
('hem. Soc. Journ. 1878, p. 464). At that time it was generally believed that sea- 
eontains no carbonates, or that at least the carbonic acid of these forms only an 
insignificant fraction of the whole carbonic acid. 
Some years ago, when I first directed my attention to the subject as part of the 
general problem of sea- water analysis, I perceived this weak point in Buchanan’s position, 
but 1 had no doubt in my mind about the soundness of the basis on which he had 
founded his analytical process — the immense gulf between his and Jacobsen’s results 
had Bomehow escaped my attention. or perhaps slipped from my memory — and I thought 
the best thing I could do would be, to apply to a selection of Challenger waters the 
following extension of his method founded (as will readily be perceived) upon the 
assumption that the total carbonic acid in a given sample of sea-water consists of three 
parts, namely, — a part “a,” which is simply absorbed ; a part “ b,” which is combined 
with the sulphates, &c. ; and a part “c” (which I presumed to be very small), which is 
pn s« nt in general as bicarbonate. To find these quantities, apply Buchanan’s method to 
a part of the sample as it is; this gives o + b+i-c. Then apply the same method to 
another part which lias previously been shaken with air to a sufficient extent to expel 
what i~ present of purely absorbed carbonic acid; this gives b + \c. To determine “c,” 
dilute the residue obtained in either distillation with gas-free water, add some hydro- 
chloric acid, and resume the distillation ; this gives the remaining \ c . 
When we tried this method with a supply of sea-water, specially procured for the 
puqw.se, we had no difficulty in working it; but the results were utterly and absolutely 
u-'-le-s, so inconstant and mutually conflicting in their evidence, as to defy all attempts at 
rational interpretation. I now know — and shall by and by explain — the cause of these 
irr* ilarities, but I did not know at the time, and accordingly deferred the consideration 
of the subject for a time, in order to direct my attention more exclusively to the exact 
dot* rmination of the saline components in a series of 21 waters, which had been 
• n’m-t- d to me as a first instalment for complete analysis. These analyses incidentally 
d t h«- greater part of the carbonic acid question. There is no need of my here 
r sj.it ulating at length what was so fully reported on in a previous part of this 
memoir (j». 20, compare also ]>p. 23 to 25). All the 21 analyses brought out an 
of h i- over the sum of muriatic and sulphuric acid equivalents, which excess 
of < inu-t !.<■ put down a.s so much carbonate. It is true the several values of the 
• ty. a- d- duced from the individual analyses, did not agree with one another, 
vd 1 my attempts at finding a more direct method for its precise determination 
But the -um total of the results left no doubt in my mind that a considerable 
