TIIE VOYAGE OF H.M.S. CHALLENGER. 
246 
to in the memoir on page 90, as Laving served for those fourteen abortive analyses 
quoted there, and as the method, moreover, was applied to sea-waters of abnormal 
salinity, it gave what I now know to be insufficiently exact results. 
While writing this summary I remembered these old experiments, and caused 
Mr. John M‘ Arthur to repeat them, on a smaller scale, and (in addition to the quantities 
«»f chlorine) to determine the quantities of bromine by our present exact method. 
Mr. Robert Anderson was directed at the same time to determine the correspond- 
ing quantities of sulphuric acid, and to adhere strictly to the method laid down on 
page 8. 
The water selected for the experiments was the remainder of that mixture of 
Challenger water samples, designated as “ II. mixture of seventy-one samples of medium 
depth waters, from 300 to 1000 fathoms inclusive” on page 98. 
First Experiment. — 2199’35 grms. of the sea-water, contained in a stoppered bottle, 
were exposed to a mixture of ice and salt until apparently nine-tenths of the whole were 
frozen, and ice and mother-liquor were then separated as far as possible by decantation 
and draining. The ice was then allowed to thaw, and both it and the mother-liquor 
were weighed after they had assumed the temperature of the laboratory. The mother- 
liquor, weighing 252'44 grms., was marked “No. I.”; the molten ice, weighing 1946'63 
grms., was preserved as “ No. II.” 
Second Experiment. — 2260‘84 grms. of the same water kept in ice and salt until 
apparently one-half had become solid, and ice and mother-liquor separated and weighed 
as in the preceding case. The mother-liquor (1096'12 grms.) was called “No. III.,” the 
molten ice ( 1 1 G3 *93 grms.) “No. IV.” 
In each of these four waters the halogen was determined and calculated as chlorine 
by that modification of Volhard’s method which has been so frequently referred to, and, in 
order to check the analyses, the absolute weights of chlorine in the two portions of 
original water operated upon were calculated, firstly, from the weights and analyses of 
the two fractions, and, secondly, from the weight of the whole and the proportion of 
chlorine in the original water, as it had been determined in the course of the bromine 
investigation (page 99). The agreement in both cases was very satisfactory. 
In each of these waters the bromine was determined by rigorous application of the 
method laid down on page 98, except that in two cases less than the equivalent of 
1 kilogram of original water was used (for obvious reasons), but care was taken in the 
- .i-e of the two mother-liquors to dilute them, before addition of silver solution, to very 
near the salinity of the original water. On the same principle, the two kinds of molten 
• a- water ice ought to have been concentrated by evaporation, but through fear of 
u ndcntH we preferred to use them as they were. The results are given in the following 
table : — 
