*240 
THE VOYAGE OF H.M.S. CHALLENGER. 
titration with nitrate of silver, and found to correspond to 31‘00 per cent, of HBr. Most 
of this preparation was diluted so as to produce “normal” acid (containing [HBr] grams 
per litre); and 106 - 5 grams of the latter, equal to very nearly 8 grams of bromine, 
utilised for a quantitative examination for chlorine. For this purpose about -j^ths of 
the halogen was precipitated by addition of a roughly standardised (acid) deci-normal 
solution of nitrate of silver, and the precipitate removed and preserved as bromide. 
The decantate was precipitated with a slight excess of silver solution, and the precipitated 
haloid chlorinated in the manner described in my memoir, to determine the chlorine 
in it. The haloid operated upon weighed, after fusion in air, 1‘9714 grams; after 
chlorination and expulsion of the chlorine by a current of dry air its weight was less 
by 0'4G61 grams. 
This loss of weight corresponds to 1’9G83 grams of pure bromide in the 1 '9714 of 
haloid used, which leaves 3*1 mgrms. of chloride of silver, or about 0'8 mgrms. of 
chlorine against the 8000 mgrms. of bromine contained in the 106 ‘5 grams of standard 
acid analysed. This means, practically, that the acid is free from the foreign halogen. 
4. Standard Hydrobromic Acid Solution. — The normal hydrobromic acid referred to 
in the last paragraph served for the preparation of a deci-normal solution for the subse- 
quent test analyses. According to the data of the synthesis, 100 grams of this solution 
should have contained 794 ’9 milligrams of bromine as hydrobromic acid. The final 
“titre”was determined by three gravimetric analyses, carried out each with 50 c.c. 
(which in each case were weighed out in grams), and one titrimetric analysis carried out 
in the way of the final chlorine determinations in the Challenger waters. 
The results were as follows: — 
100 grams of Solution contain 
Milligrams of Bromine. 
Gravimetric analysis, No. 1, 
797-4 
» n No. 2, 
797-7 
,, ,, No. 3, . . . 
796-5 
Titrimetric analysis, .... 
797-9 
Mean, 
797-4 
5. An Artificial Sea-water free from Bromine . — It was made up on the basis of the 
numlnrs found by me for the average composition of ocean-water salts, as given on page 
13H «»f the Memoir, from the following materials : — best commercial calcined magnesia, 
r- •• ntly ignited in a muffle before use; pure precipitated carbonate of lime ; pure sulphate 
'•f pMa-di ; and “ natrium chloratum purissimum ” from Trommsdorff in Erfurt, ignited in 
a pi itinum basin immediately before use. The calcined magnesia, of course, could not be 
