93 
THE VOYAGE OF H.M.S. CHALLENGER. 
In criticising these results we must not forget that in each case the small quantity of 
bromine I to be determined was diffused throughout about 500 times its weight of a 
. and that />, and />., are each dependent on the difference of two weighings of a 
hulk v apparatus which, between each weighing, was heated for hours in chlorine gas. Under 
th<- ■ in must anccs, the tare could not be expected to be absolutely constant. Supposing 
the weight of the mixed haloid and the weight of the chloride to be wrong by — 0’5 and 
+ 05 milligram respectively, this would account for an absolute error of — 1 - 8 mgrms. 
m the calculated bromine =3 per cent, of the quantity to be determined. But in the 
of Nob. 52 and 45 the loss »>f bromine amounted to 3‘6 and 5‘3 per cent. ; and even 
if we rejected these two trials (which we have no l ight to do), the high value 97'5 for dq 
in No. 46 would confront u- as all anomaly. The method is obviously subject to occa- 
- i • > 1 1 : d irregularities. These, however, I hoped, could be eliminated by a more rigorous 
adln renee to a fixed method than had prevailed in the synthetical trials, and by a 
sufficient multiplication of analyses in each case. Besides, I was unable to see my 
wav to any essential improvement upon the method adopted, and therefore now proceeded 
to the actual analyses, according to the following method : — 
Determine the “chlorine" in the water to be analysed. Then weigh out 1 kilogram 
and add to it 200 c.c. of the d< cinormal silver solution per 30 grms. of potential chloride 
of sodium present, 3*90 percent, of what would precipitate the whole of the halogen, 
collect i h<- precipitate by decantation and chlorinate it. To the mother-liquor add the 
precipitant as served for the first precipitation, and treat the precipitate 
like the first, operating otherwise as explained in the instructions given on pp. 91 and 92, 
This method wa> applied to three mixtures of Challenger waters, namely: — 
I. A mixture of 04 samples of “Surface Water,” taken from depths varying from 
0 to 50 fathoms, inclusive. 
II. A mixture of 71 samples of “ Medium-Depth Water” taken from depths varying 
from 300 to 1000 fathoms, both inclusive. 
III. \ mixture of 70 samples of “ Deep-Sea Water” taken from depths of 1500 
fathoms or more. 
A n tic ries of Challenger eimph s shallow shore-waters do not occur at all, I pro- 
• ur • i a supply of water from ofl Port Loi is, Isle of Arran, where there is abundance of 
• d » ( thin’, ii g that these vegetable growths might probably tell appreciably on the 
i nine pn 'tit in the dissolved salts), and analysed it like the rest. The 
results are given in the following tables : — 
