AMOUNT OF PHOSPHORIC ACID IN THE SEA-WATER. 257 
accurate, and as the two samples were analysed side by side they are 
fairly comparable. They show that the total phosphorus may be as 
high in summer as in winter, but that in summer only a very small part 
of it may be present as phosphoric acid. The analyses as a whole, how- 
ever, do not allow more to be stated with certaity than that there is 
a soluble phosphorus compound present other than phosphoric acid, 
that it is probably not a lower acid of phosphorus owing to the com- 
parative difficulty with which it is oxidised, and that it is probably an 
organic compound. 
The nature and origin of this ““ organic phosphorus ”’ is, of course, quite 
unknown. At first it was thought that it might be due to minute organ- 
isms which pass through a filter paper, and an attempt was made to 
filter it out by means of candles such as are used for bacteriological work, 
but this proved impossible as both Doulton and Chamberland filters gave 
up a considerable amount of phosphates to distilled water passed through 
them. It is, however, unlikely that it is due to solid particles, as if iron 
and a relatively large amount of ammonia are added to sea-water so as 
to produce a bulky precipitate of hydrates of iron, lime, and magnesium, 
which would almost certainly entangle and stop any suspended matter, 
the filtrate from this still shows a considerable amount of phosphate after 
oxidising. 
SUMMARY. 
The amount of phosphoric acid in sea-water off Plymouth was at a 
maximum of 0-06 mg. per litre of P,O, at the end of December, 1915, 
after which it fell irregularly to a minimum of less than 0-01 mg., which 
extended from the last week of April to the latter part of May; 
it then increased again and in January, 1917, reached the same value 
as the average for the first part of the month in the previous year. 
This seasonal variation is probably to be attributed to the removal of 
the phosphates from solution, at first by the fixed algze, and later in the 
spring by the diatoms and for a short time by Ph@ocystis. There is also 
present in sea-water taken near Plymouth another soluble compound 
of phosphorus which can be converted into phosphoric acid by oxidising 
agents. 
