It) 
the voyage of h.m.s. challenger. 
w , 1 is-. »1 \ ' '1 in the.* calculated volume of standard sulphuric acid. In experi- 
s to 15 a mixture of chloride of platinum solution with standard hydrochloric acid, 
. • 1 - ■ to r< present a solution of chloroplatinic acid (PtCl 6 H 2 ) was used instead of 
simple platinic chloride (PtCl 4 ). 
A :i t this table shows that although pure unmixed sulphate of soda always gave 
. pi. a mum c<jui valent to 1 2 mgrms. of potash, the tests made with 45 to 47 mgrms. 
• : 1 i ; .i - h gave in general low results, showing that to some extent the method 
, ,-\.n it- moderate degree of precision to an accidental compensation of errors, 
i • . ;d v we had not succeeded in effecting any material improvement; but I thought it 
aid < ail v do good to take 100 c.c. instead of 50c.c. of sea-water for each analysis, and 
m itter of principle it was better to use PtCl 6 H 2 than PtCl 4 . These modifications 
! ; lmjlv adopted, fixing upon 200 mgrms. of platinum (as PtCl 6 H 2 solution) as the 
proportion of reagent to be employed. 
< > t r. ipt of the third (and last) instalment of waters, we renewed our attempts to 
• up n «»ur process of potash determination, and this time succeeded at once in 
- a source of error which had so far escaped our notice. It consists in this, that 
• d platinum obtained from the mixture of sulphates and chloroplatinate of 
■ i"iain by hydrogen, under circumstances which I did not succeed in defining, is 
itly Table in dilute hydrochloric acid. The remedy is easy. The hydrochloric acid 
■ en u 1 for washing, must be treated with sulphuretted hydrogen, and the 
pit ite ( i ft • r snrac hours’ standing) be collected and ignited along with the bulk of 
1 • num. This modification was, of course, at once adopted. At first I thought it 
ibly ii"t platinum itself, but some impurity in the reagent which dissolved in 
• ld'-rie a> id ; but this proved ;i mistake. Absolutely pure chloride of platinum, 
i fi >m e < ' i n mere i ally pure metal by Schneider’s method (which removes even the 
. p! ttinum metals), yielded a metal which behaved to hydrochloric acid in the same 
manner as the metal from the ordinary “pure” reagent had done. The 
•ion of the acid on the reduced platinum is checked in a marked degree, though 
pi' vent ■ d, by the addition to the acid of strong sulphuretted hydrogen water, 
t ulplmrctted acid we often obtained filtrates absolutely free from platinum. 
!• applying the modified process to the samples of water, it was examined by 
means of test analyses. 
I' p tudi-fre. chloride of sodium was made from recrystallised bicarbonate by 
' h\ droehloric acid, the solution being evaporated until about one-half of 
'• ; i ' ry*t illi*. il out of the hot liquor. The crystalline deposit was washed with 
* ‘ ■ "f hot w iter until it was sure to be free from the mother-liquor, and 
ignited gently in platinum. 
1’ ■ prepared from the double stilt Mg(NH 4 ) 2 (C0 3 ) 2 4H 2 0 (derived 
dphat- i. _ ;,it' 1 and effectually freed from a trace of sulphuric acid, still 
