200 Dr. Marcet on the specific gravity and temperature 
laston put the question to me, whether it was not probable 
that traces of potash might be found in sea water ? I answered 
in the affirmative, and thought the fact well worthy of inves- 
tigation ;* but as no one could be better qualified than the 
Doctor himself to put his own suggestion to the test of ex- 
periment, I supplied him with sea water, and begged of him 
to favour me with his results, which he has just communi- 
cated to me in a note to the following effect : 
“ The expectation which I expressed to you that potash 
would be found in sea water as an ingredient brought down 
by rivers from the decay of land-plants, is now fully con- 
firmed by experiments on waters obtained from situations so 
remote from each other as to establish its universality. 
“ There is no difficulty in proving the presence of this in- 
gredient by muriate of platina. For though the triple mu- 
riate of platina and potash is so soluble that this reagent 
causes no precipitate from sea water in its ordinary state, yet 
when the water has been reduced by evaporation to about |-th 
part, so that the common salt is beginning to separate by 
crystallization, the muriate of platina then causes a copious 
precipitate. 
“ If this precipitate be mixed with a little sugar and heated, 
the platina is reduced, and muriate of potash may be sepa- 
rated from it b}^ water, and the nature of its base shown by 
its yielding crystals of nitrate of potash with nitric acid. 
<£ I evaporated a pint of the water which you sent me (marked 
No. 9, specific gravity 1026,22) taken up by Captain Ross in 
* I, in my turn, pat the question to Dr. Wollaston whether it was not pro- 
bable that minute quantities of all soluble substances in nature might be detected in 
sea water ? 
