I 



CHEMICAL ANALYSIS 45 



imitated with standard nitrite solution in the same way as 

 Nesslerizing,^ taking care that the original and the imitation 

 are started at the same time, and read off in not less than 

 twenty minutes. 



Organic Nitrogen. — As it has been proved that the organic 

 matter in water is altered by distillation, and also changes 

 rapidly on standing, I sought to devise a process which should, 

 without distilling, obtain the results of a number of sewages 

 quickly and comparatively, and yet with sufficient accuracy. 

 I adopted the following modification of the well-known Kjeldahl 

 process to ascertain the unoxidized nitrogen, to which I attach 

 great importance in its relation to the oxidized nitrogen repre- 

 sented by the nitrates and nitrites. The quantities used for 

 analysis are regulated by the strength of the liquid, and are, 

 of course, larger for an average effluent than for a raw sewage. 

 The amount aimed at in the final Nessler titration is such as 

 will correspond to i c.c. of the original sewage or 5 c.c. 

 effluent, as that quantity, made up to 50 c.c. with ammonia- 

 free water, generally gives a suitable colour. 



Free Ammonia. — One c.c. of the settled sewage or effluent 

 is diluted to 50 c.c. and Nesslerized, as in Chapter II., 

 p. 35. The figure obtained is the actual saline ammonia 

 present. 



Kjeldahl. — Ten c.c. of a sewage, or, say, 100 c.c. of an effluent 

 + 4 c.c. of pure sulphuric acid are heated in a pear-shaped hard 

 glass flask in a slanting position until the liquid becomes colour- 

 less. When about 3 c.c. remain, the flask is cooled and washed 

 out with small quantities of ammonia-free water into a 100 c.c. 

 measure, until the volume of the liquid reaches about 40 c.c. 

 An excess — i.e., about 25 c.c. — of soda solution (25 per cent.) free 

 from ammonia is now added, when a flocculent precipitate is 

 thrown down. After cooling, the liquid is made up to 100 c.c, 

 transferred to a clean and dry stoppered bottle, and rotated at 

 intervals until the flocculi — which at first float entangled with 

 air-bubbles — subside. A suitable fraction of the clear liquid 

 is then pipetted into a Nessler glass, diluted to 50 c.c, and 

 Nesslerized. This gives the total unoxidized nitrogen in terms of 

 ammonia. The free NH3, as found above, is subtracted, and 

 the remainder calculated into "organic nitrogen (Kjeldahl)." 

 A blank is done with the reagents. 



^ See Sutton's "Volumetric Analysis," 1896, pp. 404, 435; also Rideal on 

 " Nitrites in Waters and Sewages," Journal of State Medicine, June, 1902, p. 333. 



