ScJiuette—Biochemical Study of Lake Mendota Plankton 603 
Sample 
Total sulphur 
Nature of catch 
A 
0.60% 
plant 
B 
.61 
plant 
C 
.60 
animal 
D 
.64 
animal 
E 
.64 
plant 
154 
.63 
animal 
112 
.42 
mixed 
168 
.60 
plant 
No data on the sulphur content of marine plankton are avail¬ 
able. 
Total phosphorus. The phosphorus content was determined 
by the method of the Association of Official Agricultural Chem¬ 
ists with the following modification. The material under ex¬ 
amination was treated with an alcoliolic solution of magnesium 
nitrate, evaporated to dryness, and ignited. Silica was removed 
by the method outlined in a previous paragraph and the phos¬ 
phorus precipitated in the filtrate as ammonium phospho- 
molybdate. This precipitate was dissolved in ammonia and 
the phosphorus precipitated with magnesia mixture, collected 
on a filter, ignited and weighed as magnesium pyrophosphate. 
The range of values is within narrow limits as shown by the 
following table: 
Sample 
A 
B 
C 
D 
E 
154 
Total phosphorus 
1.07% 
0.91 
1.22 
1.41 
1.40 
1.57 
No results of the phosphorus content of marine plankton 
have been published. 
Nitrogen. Experiments were made to determine the amounts 
of several forms of nitrogen present. 
Protein nitrogen was determined by heating the sample under 
examination with water, adding a measured volume of moist 
cupric hydroxide (Stutzer’s reagent) and filtering when the 
solution had cooled. The nitrogen in the washed precipitate 
