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-water was 0-044 ing. per litre ; this showed signs of an increase when the supply of land-water rose after rain. The figures are much lower than those found by Raben for the Baltic and North Sea.

4. The amounts found by another method during the previous spring and summer are higher, but the figures cannot be considered quite trustworthy.