AMOUNT OF PHOSPHORIC ACID IN THE SEA-WATER. 255 
Total P 
Phosphates. P.O; mg. per litre. calculated 
Date. G.M.T. 8.%.. Found in duplicates. Mean. to P.O- 
mg. per litre. 
Jan. 24 11.20 a.m. 33°42 0-0378, 0-0391 0-0384 == 
Feb. 5 12.30 p.m. 31-58 0-0507, 0-0414 0-0460 a 
elt | LO4 cae = 0-0190, 0-0190 — (0-0190) 0-0323 
eae. tll Os saci 33°30 0-0371, 0-0343 0-0357 ——= 
Mar 11.40 a.m. 33-82 as 0-0350 0-039 
i 
eo) Toh acm, 34-54 0-0201, 0-0115 0-0158 — 
5p A, a Oe ee 34°54 0-0101, 0-0122 0-O111 0-050 
ee 2s bh AD am. 32°18 0-0104, 0:0148 0-0126 0-045 
Aprile Ga" 11.55 a.m. 34-40 0-0160, 0-0180 0-0170 0-016 
eee LO an, 34:40 — 0-0056 ~- 
ages) — 34-40 0-0117, 0-0124 0-0120 0-035 
May 9 10-50 a.m. 34-16 0-0158, 0-0130 0-0144 0-046 
pee. AD am. 34-60 0-0053, 0-0064 0-0058 a 
June 19 10.45 a.m. 34-90 0-0185, 0-0184 0-0184 0-036 
ete 10 45:3. — 0-0230, 0-0248 0-0239 0-038 
Sept. 13 noon — 0-0277, 0-0198  0-0238 0-024 
Oct: 19 10.45 a.m. ooL08 0-0194, 0-0155 0-0174 0-029 
1917 
Jan. 10 12.30 p.m. 33°62 0-0435, 0-0448 0-0442 0-049 
In the first place it is clear that the results given in the previous 
paper which were obtained by precipitating the phosphorus with iron 
and then weighing as phosphomolybdic anhydride are seriously in error, 
and it was found that molybdic acid was thrown down at the same 
time. 
The data of the present table show that there is a large seasonal 
variation, the maximum being more than ten times as large as the 
minimum. At first it was expected that the curve would agree with that 
for the phytoplankton inverted, but this is not the case. Miss Lebour* 
has made counts of the diatoms at the surface, 5 fthms. and 7 fthms. 
on 330 samples taken on 110 days at the Knap Buoy from September 21, 
1915, to September 18, 1916. The average number in | ccm. for October, 
1915, was 17, and in November 9, while in December and in January, 
February and March, 1916, there were only one or two. The maximum 
number for the year, 38, occurred in April, 1916, the high value being 
due to the last week of the month, 45 bemg counted on the 25th and 137 
on the 27th. Then a decline set in, with 30 per cubic centimetre in May 
and only 9 in June. In July there was a rise to 21 and a secondary 
* Lebour, Marie V., M.Sc., ‘‘ The Microplankton of Plymouth Sound from the Region 
beyond the Breakwater.” This Journal and Volume, p. 133. 
