r, 
THE VOYAGE OF 101.6. CHALLENGER. 
• - , uj, • j ,*\ 7 iorn\<d solution of tins suit in stock, and wlion deci-normal was 
r , . r , : t -. i»r- pare it l»y diluting the correct weight of this strong solution with water 
• .% litr s. the titn of the dilute solution being, of course, confirmed by direct 
• umj^rison with the standard silver solution. 
I ('• (■ si null Solutions were made synthetically from the deci-normal ones, and 
• • .nst . ach other volumetrically. We found it expedient to add some iron alum 
... t» ; . s-il;.hitf\ mate, to give it a distinctive colour. It will be understood that although 
. wriv all d«*ei- or centi-normal in the volumetric sense, in the Jin&l analyses 
].. nd. d on the exactitude of burette or pipette measurement, except the deter- 
: small excess of silver present in the mixture of weighed sea-water and 
i rrighed standard silver solution. 
In the preliminary analyses the sea-water (5 c.c. in each case) and the standard 
hit an w- r. measured by volume, the latter in Mohr’s burettes. As already stated, I 
! .in.d it imp. i-siblc to obtain sharp results by titrating the excess of silver with sulpho- 
, it. n th pp - nee of the chloride of silver precipitate. For this it is easy to account 
■ > . ,i r . illy. Supposing we add a slight excess of nitrate of silver to a given solution of 
id.-, . : ’id then (in the presence of iron alum) exactly neutralise the excess of silver 
dph" ■ v . i u a t < i of ammonium, another drop of this solution will produce ferric sulplio- 
\ tn , but the ■ .lour cannot be seen distinctly before the precipitate has to some extent 
•• .nd hefor- it has done so the ferric sulphocyanate will have been decomposed by 
in - t « ld<»ride of silver present (Fe(NCS) 3 4- 3AgCl = 3AgNCS + FeCl 3 ) ; in 
fact part "f the (NCS)NH, adi led will act directly upon the AgCl instead of on the AgN0 3 . 
\: • will on until an appreciable excess of NCS has been added, so that the 
. .... -a : vi\ ■ - the settling process. If I am right thus far the remedy would appear to 
Aid a considerable excess of nitrate of silver from the first, so that, before the 
■nit of the reaction comes on, there is enough of (NCS)Ag in the precipitate to 
• :!■ i 11 \ i -mbit the reaction above formulated; in this fashion: 3AgNCS + FeCl s = 
3AgCl + Fc(NCS) 8 . This condition (according to a series of incidental observations made) 
. . • ■ fulfilled wh* n, for about 25 c.c. of decimal silver-solution needed, 4-5 extra c.c. 
v added to be titrated by the sulphocyanate solution. As the preliminary 
* i it i* .»i - were effected only for our own guidance, 1 did not find it worth while 
t; limit, ly into the matter by a series of systematic experiments. Having 
• ii ; ml-, r of chlorine titrations, both by the original Volhard process and 
in* life it ion of the -iimc, I, of course, came into possession of extensive 
■ • ’ ' * tic < i : •! which the former gave in our hands; but, useful as these 
• \j- n * - v.* p t.. u , tie ir reproduction in this place could serve no useful purpose. 
\ • f • .act chlorine determinations had been made and booked for 
r • r* t._\ i. "* 111 * im id* ii tal observations made in the laboratory shook my faith in 
• ”1 * t uncomfortable manner. In endeavouring by its means to 
