608 Wisconsin Academy of Sciences^ Arts, and Letters, 
anhydrous sodium sulphate. Twenty-five cc. of the filtrate 
yielded an amount of cupric oxide by the Defren-0’Sullivan 
method equivalent to 29.3 mg, dextrose. The amount of re¬ 
ducing sugar found when calculated as dextrose is 3.12%. The 
solution was hydrolyzed by letting it stand over night with 5 ce. 
of concentrated hydrochloric acid. No change in reducing 
power was found under -these conditions. This indicates the 
absence of a disaccharide or a glueoside. 
The colloidal nature of the extract obtained from the algal 
catch under similar conditions precluded a quantitative 
determination of reducing sugars. A good reaction was ob- 
tainedj however, with Molisch’s reagent. 
The work of Hoagland^ and of Stanford^ on the algin 
of marine kelps lent interest to the isolation of a similar car¬ 
bohydrate constituent from our fresh water plankton. Five 
grams of material were digested cold for 24 hours with a two 
per cent solution of sodium carbonate. The supernatant liquid 
was decanted and the residue thoroughly washed with cold 
water. From the combined filtrate and washings dilute hy¬ 
drochloric acid caused no precipitation. This indicates the 
absence of a substance comparable to their algin. 
The furfural obtained on distillation with hydrochloric acid 
T>f specific gravity 1.06 when calculated to pentosans was as 
follows: 
Sample 
A. ...... 
B. ...... 
0 ....... 
D. ...... 
E. ...... 
154.. .... 
5158.. ... 
Pentosans 
2.67% 
3.00 
1,30 
1.14 
3.42 
0.78 
2.30® 
Inasmuch as the plankton catches alluded to in the introduc¬ 
tion of this paper are rarely pure, being for the most part mix¬ 
tures of vegetable and animal forms, it seemed desirable to 
find some chemical method whereby the composition of a plank¬ 
ton catch may be determined with a fair degree of certainty 
i Loc. cit. 
^Loc, cit. 
® Analysis by G. M. Bishop of the Survey, 
