Adeney — Dissolved Gases and Fermentative Changes. 557 



Methods employed for the determination of Inorganic Nitrogen. 



The nitrogen as ammonia has been determined in the ordinary way by 

 nesslerizing after distillation, with the exception of a few cases, when it was 

 necessary to directly nesslerize without previous distillation, owing to the fact 

 that the substances experimented with were decomposed on boiling. 



The method employed for estimating the nitric acid was that which has been 

 worked out by Williams,* and which depends upon the action of a " zinc- copper 

 couple" in reducing nitrates and nitrites to ammonia. My general experience 

 with this method is, that it gives reliable results. 



For the estimation of nitrous acid, I have employed Griess' metaphenylene- 

 diamine method, as detailed in Sutton's *' Volumetric Analysis," p. 367, 5th 

 edition. 



Wherever possible, that is when the total quantity of inorganic nitrogen has 

 not been large, I have preferred to subject the water to the action of the " zinc- 

 copper couple" before distilling off the free ammonia present. 



The nitrogen as free ammonia then obtained, after the action of the couple, 

 represents the total inorganic nitrogen. This amount, less that as free ammonia 

 originally present, and nitrous acid, which are separately determined, gives the 

 nitrogen present as nitric acid. 



Wlien, however, the free ammonia or nitrous acid is present in large quantity, 

 I have separated them in the ordinary way, the free ammonia by distillation, and 

 the nitrous acid by distillation in the presence of an excess of ammonium chloride, 

 before examining the water for nitric acid. I have occasionally employed Crum's 

 method with Lunge's nitrometer to check the results obtained with the zinc-copper 

 couple method, and have usually obtained concordant results therewith. 



Errors. 



The methods of experiment which I have described are liable to three distinct 

 sources of error. They are : — 



1. The possible changes in volume which the dissolved gases may suffer during 

 the manipulation necessary for bottling the water, and transferring it to the gas 

 analysis apparatus. 



2. The operations in the gas analysis apparatus, viz. the extraction and 

 analysis of the dissolved gases. 



* C. S. J., 1881, 100. 



4 K2 



