750 DR CHARLES HUNTER STEWART ON THE ESTIMATION OF 



Added June 1894. 



Application of the Kjeldahl Method to the Analysis of Potable Waters. 



The application of the Kjeldahl process (for the determination of nitrogen) to the 

 analysis of potable waters has been a good deal studied both in this country and 

 America. In 1888 Dr J. A. Blair worked at it in the Public Health Laboratory of the 

 University of Edinburgh, and his results were submitted as a Thesis. 



Messrs Drown and Martin* give an account of its application to a number of potable 

 waters in America, and also the comparison between the amount of albuminoid ammonia 

 got by the Wanklyn method and the organic nitrogen calculated as ammonia by the 

 Kjeldahl method. In ninety-one surface waters examined by them they found the 

 following as an average : — 



Albuminoid Ammonia, Wanklyn. Organic Ammonia, Kjeldahl. 



0-0224 per 100,000 0"04958 



Converting the Kjeldahl results into nitrogen, we have organic nitrogen, 0"0408 



They consider the addition of permanganate of potassium unnecessary in the operation. 



Regarding the influence of nitrates or nitrites, they say : " We have not found that 

 the presence of nitrates and nitrites in water interferes with the accurate determination 

 of the organic nitrogen. The error, which has been found by Kjeldahl and Warrington 

 to be caused by nitrates in the determination of organic nitrogen, seems to disappear 

 under the conditions of great dilution which we have in natural waters." 



This statement is founded on the following experiments. From a large vessel of 

 water three different portions of 500 c.c. each were taken. 



No. 1. No. 2. No. 3. 



With nothing added. With 07 mgrms., KN0 3 . With 0-6 mgrms., KNO a . 

 Organic nitrogen, . . . 00354 0"0354 0"0365 



This point will be referred to later. 



* Chemical News, vol. 59, p. 272 (1889). 



