Abe-sey— Aerobic Bacterial Fermentation. 



9 



The capacities of the flasks were veiy carefully determined. They 

 varied from about 540 c.c. to about 600 c.c. ; and usually the volume 

 of solution employed was about 400 c.c. for each flask. 



Eoth bottles and flasks were immersed in distilled water, neck 

 downwards, in large glass vessels, which were themselves covered with 

 glass plates, and kept in the dark at an equable temperature. 



Composition of Solution employed. 



The solutions employed have all been made of the same strength, 

 viz., 0*225 grm. urea, and 0-1 grm. each of potassium phosphate, 

 potassium chloride, and sodium carbonate per litre. This quantity of 

 urea is equivalent to 83*7 c.c. carbon dioxide, measured at 0° and 

 760 mm., and 0-105 grm. of nitrogen. Solutions of this strength 

 have been found very convenient, because the fermentations have not 

 been sufficiently rapid in them to set up anaerobic conditions in the 

 lower layers of liquid when not exposed to a temperature higher 

 than 21° C. 



Methods of Determining the Organic and the Inorganic Nitrogen. 



For the determination of the organic and inorganic nitrogen, as 

 dilute solutions as possible were in all cases employed, the strength 

 taken being just sufficient to give distinctly the necessary colour 

 reactions. 



The nitrogen as ammonia has been determined by direct nessler- 

 ising. 



Nitrogen in the form of nitrite has been determined by the meta- 

 phenylene diamine method. 



In all cases the total inorganic nitrogen has also been determined by 

 the zinc- copper couple, and nitrogen as nitrate sought for ; but no 

 distinct evidence has been found of its presence in any of the solutions 

 in which the fermentation was not allowed to proceed to completion. 



The organic nitrogen, together with ammonia, if present, has 

 been determined by evaporation and ignition with small quantities 

 of concentrated sulphuric acid, not exceeding 1 to 2 c.c. The acid 

 solution was rendered alkaline, and the ammonia distilled off, as in 

 Xjeldhal's process. 



