AMOUNT OF PHOSPHORIC ACID IN THE SEA-WATER. 129 
A few points come out clearly from the results. 
In the first place, the results are much lower than those obtained by 
Raben for the Baltic and North Sea, his lowest being 0-14 mg. per Jitre 
against 0-1 mg., the highest found at Plymouth. The salinity at the 
Knap Buoy is nominally 33-5 per thousand up to nearly <5, comparable 
with a large part of the North Sea. But the North Sea receives enough 
fresh water from the great rivers of Russia and Germany to keep the 
salinity of nearly the whole of it below © 5 per thousand, while the effect 
of the land drainage in the western part of the English Channel is con- 
fined to a comparatively narrow band along the coast. The effect of an 
increased supply of land water in increasing the phosphoric acid is seen 
in the results for December 20 and January 3, when the salinity was very 
low ; a sudden rise occurred then after the figures had been fairly con- 
stant for two months or more. This rise did not show itself till a few 
days after the salinity had fallen, which suggests that much of the phos- 
phorus from the land enters the sea in an incompletely oxidised form 
and is then converted, by bacterial action, into phosphoric acid. 
If the earlier eravimetric results are taken as correct there is a decided 
seasonal change, the higher values being found in spring and summer, 
but the writer is not inclined to place much confidence in them. The 
experiments are being continued and it is hoped that the next few months 
will settle the question. 
It is unfortunate that so far it has not been possible to obtain samples 
at a greater distance from shore, as it may be that the increased phos- 
phorie acid found after oxidation is a purely littoral or estuarine phe- 
nomenon resulting from the form in which part of the phosphoric acid 
is carried down by land-water. It does not seem likely that it arises 
from diatoms or bacteria which pass through a paper filter, as the same 
increase was noticed on oxidising a filtrate from a solution in which iron 
had been precipitated by ammonia, a very efficient method of removing 
the finest suspended particles. The approximately constant ratio of 
the two forms of phosphorus is also an objection te this explanation. 
SUMMARY. 
1. Phosphoric acid in sea-water may be determined with an accuracy 
of about 0-003 mg. per litre by concentration with iron and colorimetric 
examination. 
2. If the sea-water be previously oxidised by potassium permanganate 
the amount found is considerably increased. 
3. From September, 1915, to February, 1916, the average amount of 
phosphoric acid in water collected half a mile outside Plymouth Break- 
NEW SERIES.—VOL. XI. NO. 1. MARCH, 1916. I 
