254 DONALD J. MATTHEWS. 
paper was 0-0036 mg. of P,O;. A repurification of the iron, acids, alkali 
and water reduced it to 0-0026 mg., and a second purification to 0-0021 mg. 
The blank on the amounts required for the estimation of total phosphorus 
was at first 0-0066 mg. and afterwards 0-0061 mg. The blanks were 
determined both by carrying out analyses on distilled water, to which 
00300 mg. of P,O; had been added, and also with small amounts of 
water, the final solution being made up to 10 ccm. and compared in a 
special small colorimeter tube holding only 10 cem. The results agreed 
excellently. 
The determination of the small amounts of phosphoric acid found 
during the summer presented considerable difficulty. Making the final 
volume 10 ccm. gave rather discordant results, and it was subsequently 
found that the closest agreement was obtained between duplicates if 
enough of the standard solution was added to the sample to bring the 
content up to about 0-035 mg. of P,O; per litre, the final volume being 
50 ccm. This gives a strong colour in a depth of 40 mm. and at the same 
time avoids the errors which arise when very small volumes of liquid are to 
be manipulated. 
The whole of the results obtained by the colorimetric method are given 
in the following table, and those for phosphoric acid are plotted in the 
curve ; the figures for February 17th, 1915, have not been used in this 
case as the sample was by an oversight allowed to stand unsterilised for 
six days. 
SURFACE SAMPLES TAKEN AT THE KNAP BUOY. 
Total P 
Phosphates. P.O; mg. per litre. calculated 
Date. G.M.T. S.%,. Found in duplicates. Mean. to P.O; 
mg. per litre. 
Seprazios 10/30aim. 34:96 — 0-046 —- 
S24 55 aan: 34-78 0-042, 0-041 0-0415 — 
26) 1145 a.m. 34:43 0-040, 0-034 0-037 — 
29 «11.10 am... <34:14 0-040, 0-037 0-0385 = 
Dec. 2 12.20 p.m. — 0-0484, 0-0435 0-0460 — 
od on 10250 "a om old G 0-049, 0-047 0-048 = 
peaks. /lde30ra am: —- 0-044, 0-041 0:0425 — 
Ge 12.10ip am: 26-20 — 0-043 — 
ae 200 11, 25%a5m, 29-69 0-058, 0-064 0-061 — 
Jans 83 11-35-aam.:--- 25:66 0-057, 0-057 0-057 — 
14 155 p.m. 33-87 0-0318, 0-0316 = 0-0317 — 
18 2.30 p.m. 33:93 ° 0-0336, 0-0348 0-0342 — 
