120 STUDIES OF PHOTO-SYNTHESIS IN MARINE ALG.E 



analysis for nitrite and nitrate gave in both cases 1 in 10 million to 

 1 in 15 million expressed as nitrogen. It follows that the nitrogen 

 converted by the growth in light of the algae could not be obtained 

 from combined nitrogen as ammonia, nitrite, or nitrate. The only 

 other available source is dissolved nitrogen in the sea water derived 

 from the air. 



A glance at the fifth column of the table given below shows that 

 the four jars, closed airtight but kept in sunshine, fixed nitrogen 

 almost as rapidly as the open jars in sunshine. This furnishes proof 

 that the source of the nitrogen fixed is not the nitrogen peroxide, 

 or so-called ozone, of the air, but the elemental nitrogen. This 

 does not, of course, exclude nitrogen peroxide as a nutrient 

 and a stimulant; experiments in the preceding chapter on 

 fresh-water algae have shown that dilute nitrogen peroxide can 

 so stimulate growth. But both series of experiments agree in 

 proving that, given an ample supply of carbon either as carbon 

 dioxide or as bicarbonate and the presence of light- energy, then 

 elemental nitrogen from the air in solution in the nutrient medium 

 can be fixed and built up into organic compounds. At the con- 

 clusion of the series of experiments, the four samples of weed in each 

 set of four bottles were separated from the sea water, united, pressed 

 between filter-papers, and the moist weight taken. As at the out- 

 set 0-5 grm. was weighed out into each jar, the initial weight in each 

 set was 2 grm. 



After weighing, each set of weed was placed in a wide-mouthed 

 glass- stoppered bottle, and preserved in a quantity of about 80 c.c. 

 of absolute alcohol. 



When the analyses were started, the preliminary step in each 

 case was to evaporate off the alcohol in a weighed capsule, add the 

 preserved weed, and dry to constant weight; these dried weights 

 are recorded in column 4 of the table. Then each dried weight was 

 analysed for nitrogen by the usual Kjeldahl method, and the results 

 are given in column 5. 



Commentary on Table. The figures given in column 2 show 

 the alkalinity developed by the photo-synthesis. Notice how much 

 greater it is in full light than in diffuse light, and that in complete 

 darkness it becomes negative because the carbon dioxide discharged 

 in oxidative processes in darkness renders the sea water acid to 

 phenolphthaleiin. The normal sea water at this period possessed an 

 alkalinity to this indicator represented by about 2-5 c.c. per 100 c.c. 



