388 Prof. J. Joly on the 
very sure that errors arising from contamination did not enter 
these results, it seemed probable that some other source of 
error existed. If this arose from any cause residing in the 
nature of* the material dealt with, it could only be that there 
was in some way concealment of the emanation in the lower 
results, and that the higher results were the more nearly 
approximate to the truth. Sea-water is rich in sulphates ; 
and the possibility of the process of concentration resulting 
in a precipitation of the radium in non-emanating form 
occurred to me. There is a small quantity of barium in sea- 
water. A very minute precipitate of this might bring with 
it the radium ; and, again, the calcium sulphate, which is 
one of the earliest substances to fall, might also be concerned. 
The emanation, which never increases beyond a certain 
amount, might be imprisoned in very fine precipitated 
particles. The flasks were examined with this possibility in 
view. None of them were perfectly clear of precipitate. Iu 
(a) it was least, perhaps ; but the dulling of the glass on the 
inside of the flasks showed that in every case some solid 
matter had come down. It is true that, in so far as this is 
redissolved on ebullition, it can do no harm ; but the risk of 
error here was evident. 
Accordingly all five were somewhat diluted and trans- 
ferred to larger flasks, and a few c.cs. of very pure HC1 
(which I had distilled from a nearly pure acid) added to each. 
This instantly cleared the precipitates away. They were then 
boiled and closed. When in due time the whole five came 
to be redetermined, the results came out as follows : — 
(a) Valencia, taken in March, 0'0400 X 10 ~ 12 . 
(b) Isle of Man, taken in April, 0'0386 x 10" 1 -. 
(c) 65 miles W. of Valencia, June, 0'0314 x 10" 1 -. 
{d) 1-5 miles S. of Crow Head, June, 0*0226 X 10~ 12 . 
0?) 20 miles W. of Bantry Bay, June, 0-0303 x 10 ~ 12 . 
These, with the exception of (d), are in close agreement ; 
and I find it hard to believe that such a degree of uniformity 
could arise without a real basis for the results. The deficiency 
of (d) might originate in a loss of radium in the process of 
evaporation, the radium being in part left as a precipitate 
clinging to the evaporating dish. The higher results appear 
to be the more reliable ; indeed, there is the possibility that, 
in a liquid so rich in sulphates, even these are not a full 
revelation. I do not regard this, however, as probable. 
These results, of course, do not warrant the conclusion that 
mid-ocean sea-water is equally rich in radium. It might be 
