Joty—The Radioactivity of Sea- Water. 250 
experiments on known quantities of uraninite in solution, 
that this mode of extraction gives a somewhat lower constant 
for the electroscope, showing that it is capable of effecting a more 
complete extraction. The change in manipulation was therefore 
in favour of giving a higher, and not lower, result. 
Shortly after this measurement, Mr. Kemp sent me three other 
samples of sea-water. Calling the two samples already referred 
to (a) and (b) respectively— 
Sample (c) is from lat. 51° 26’ N., long. 12° 6’ W. A 
point about 65 miles due west of Valencia. Quantity, 2665 c.cs. 
Sample (d) is from 1°5 miles south of Crow Head, Co. Kerry. 
Quantity, 2740 c.es. 
Sample (¢) is from lat. 51° 35’ N., long. 10° 43’ W.—that is, 
about twenty miles west of Bantry Bay. Quantity, 2764 ccs. 
The last two samples were collected on the same day, June 21st. 
These were evaporated down as before, each to about 900 or 
1000 ccs. The results were as follows :— 
@) 00126) 10": 
(d) 0°0152 x 10. 
(e) 0:0268 x 107%. 
It will be seen that all these figures are of the same order 
of magnitude as the result on the Valencia water. ‘he discre- 
paney with the Isle of Man sample is considerable. While very 
sure that errors arising from contamination did not enter these 
results, if 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 conceal- 
ment 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 a 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. In (a) it was least, 
