Study of Sjrirogyra nidda, 205 



dry substance remaining was carefully burnt, when another 

 loss in weight occurred corresponding to 7.54 per cent. The 

 ash, after this treatment, was 2.52 per cent, of the original 

 material. Sfrirogyra nitida then contains:— 



Water 89.., 



Dry matter 7-54 



Ash 2.5 



Total 100.00 



G. Mann,* gives for a mixture of .S". nitida and S.jugalis 



Water 96.8 % 



Dry matter 2.72^. 



Ash 48 # 



Total 100.00 



which differs widely from the results obtained in this labo- 

 ratory with pure Spirogyra nitida. Several determinations 

 were made with material gathered on different days, but 

 the results were practically in accord. 



Combustions. 



While Mann, in the paper cited, gives the water, dry 

 matter and ash, he makes no mention of an analysis for 

 carbon, hydrogen, nitrogen and oxygen. In fact such an 

 analvsis has not been found in the literature on algse. 

 Therefore, in order to determine the primary composition, 

 a series of combustions was made under the following 

 conditions : — 



The plant was removed from the pond on a clear, cool 

 day in early October. It was prepared for use as previously 

 described, then dried at no C. to constant weight. The 

 same material was used for the entire series of combustions, 

 and after each portion had been removed from the weigh- 

 ing bottle the remainder was again heated to 1 io° C. This 

 precaution is necessary in order to secure uniform samples, 

 since the finely divided material is exceedingly hygroscopic. 



*Proc. Bot. Soc, Edinburgh, Vol. 18, (1890). 



