REPORT ON THE COMPOSITION OE OCEAN-WATER. 
80 
III.— THE BROMINE IN OCEAN WATER. 
The chlorine in the 77 sea- water analyses, tabulated on pages 23 to 25, includes 
the bromine and iodine, in the sense that [Br] parts of the former or [I] parts 
of the latter are put down as [Cl] parts of chlorine. Now the proportion of iodine* 
in sea-water is so very minute, that its effect on the chlorine determinations may 
well be neglected ; but with the bromine the case is different, for, according to all author- 
ities, it forms quite an appreciable fraction of the total halogen. In regard, however, 
to the numerical ratio of the bromine to the chlorine, the several analysts differ widely 
from one another. Justus Roth, in his Allgemeine und chemische Geologie, vol. i. 
pp. 505 et seq., quotes a number of sea- water analyses by the authorities to be named, 
whose results for the bromine, when reduced to 100 parts of total salts, are as follows : — 
C. Schmidt, 1877, ..... 0T36 and 0T44 
Von Bibra, 1851, ..... P01 „ 089 
Thorpe and Morton, 1870, ..... 0*181 
J. Hunter, in 13 analyses of waters collected S.S.W. of Ireland (1869), finds values 
oscillating about 1 ‘0. The results, as we see, vary from 0T36 to about seven times this value. 
Considering these immense divergences, I thought it would be well to try and 
determine the bromine in at least a selection of Challenger waters, the more so as, just 
on account of the smallness of its proportion, I had a chance of proving that this value 
is different for different ocean waters. 
A few preliminary determinations sufficed to show that von Bibra’s and Hunter’s results 
are far too high, while Thorpe and Morton’s or Schmidt’s come at least near the truth. 
Hence an exact determination of the bromine could not be attempted with less than a 
whole litre of sea-water, meaning 2 litres for a duplicate analysis, which is very con- 
siderably more than I could have spared of any one of my samples. I had not, moreover, 
the time for a very extensive series of analyses, and therefore at once decided upon 
preparing mixtures of waters representative of certain regions of the ocean (or certain 
depths in a given region), and analysing these mixtures. 
For the quantitative determination of the bromine contained in a small quantity of 
bromide diffused throughout a large mass of chloride only one method is known. We 
must separate out the bromine by fractional precipitation with nitrate of silver, and in 
the precipitate — which in the case of sea-water always consists mostly of chloride — 
determine the bromine by heating the mixed precipitate in chlorine gas, and ascertaining 
the loss of weight resulting from this operation. In it every [AgBr] parts of bromide of 
* See the memoir hy J. Kottstorfer, Zeitschrift fur Analytisclie Chemie, 1878, p. 305 ; also J ahresbericht fit r Clxcmu, 
1878, p. 1043. He finds one milligram of iodine in fifty litres of the water of the Adriatic. In a few experiments with 
Challenger samples I found similar values. 
(PHYS. CHEM. CHALL. EXP. — PART I. 1884.) 
A 12 
