Radioactivity of Sea-Water. 389 
that the acid-treatment is effective in bringing into solution 
suspended radioactive particles of coastal origin. 
It will be evident that measurements made on sea-salts 
must be unreliable ; for there is no assurance that the sample 
used will contain its due share of the radium which wonld be 
carried down among the first constituents precipitated in the 
preparation of the salt. 
Shortly after the above results were communicated to the 
Roval Dublin Society, five samples of oceanic water collected 
in the course of a voyage from Madeira to the Bay of Biscay 
by Dr. F. Stevenson reached me. I will call these/', 5/, h, i,j, 
for convenience of reference; giving their place of derivation 
later on. 
Fully realizing the necessity of every precaution, Dr. 
Stevenson had himself cleansed the vessels in which these 
waters were transmitted, not only with fresh- water but several 
times with sea-water, before finally filling up. 
As there was sufficient of each sample to enable two 
determinations tu be made, I resolved to vary the procedure 
in the several observations. 
/'. (1) A quantity amounting to 2825 c.cs. was evaporated 
on the water-bath in my laboratory to 15U0 c.cs. and 
tested without addition of acid. The result was 
0*0029 X 10~ 12 . This was now acidified with 12 c.cs. 
of pure radium-free HC1, the subsequent examination 
now gave 00144 x 10 - 12 . 
(2) 1650 c.cs. concentrated by evaporation in my labora- 
tory, acidified with 80 c.cs.HCl, closed and examined: 
result 0-0150 x 10~ 12 . Tested a second time the 
result was 0*0213 x 10- 12 . 
g. (1) 2S26 c.cs. concentrated in my laboratorv to 1500 c.cs. 
and acidified with 30 c.cs. HCI gave 0*0193 x 10~ 12 . 
Tested a second 'time, adding 50 c.cs. HCI, result 
0*0273 x 10- 12 . 
(2) 1500 c.cs. not concentrated but directlv transferred 
to the flask, adding 80 c.cs.HCl, afforded : 0044 x 10" 12 . 
A second experiment on this gave 0*0080 X 10~ 12 . 
li. (1) 2500 c.cs. concentrated in the Botanical Laboratory, 
T.C.D. (a new building in which no radioactive work 
had been done), with 10 c.cs. HCi gave 0*0020 x L0~ 12 . 
Tested again with addition of 50 c.cs. HCI, the reading- 
was 0*0140' x 10- 12 . 
(2) 162(3 c.cs. with 70 c.cs. HCI concentrated in Botanical 
Laboratory: 0*0084 x 10~ 12 . 
