CHEMISTRY. 521 



Determination of Organic Matter in Potable Water. 



Prof. J. W, Mallet, in compliance with the instructions of the National 

 Board of Health, has made a thorough investigation of the chemical 

 methods in use for the determination of organic matter in the potable 

 waters. Assisted by Mr. W. A. Noyes, Dr. Charles Smart, and Dr. J. 

 A. Tanner, he examined the merits and demerits of the "combustion 

 process," the " albuminoid-ammonia process," and the " permanganate 

 process." The special conclusions as to the combustion process may be 

 briefly stated : The combustion itself, carried out according to Frank- 

 land's directions, is a process of great delicacy and satisfactory in trained 

 hands ; it requires constant practice to secure good results ; the defect- 

 ive point is tbe failure of the evaporation to leave a residue represent- 

 ing the original organic matter of the water, a loss in carbon and a gain 

 in nitrogen being constant errors ; the dissociation of ammonia salts 

 during the evaporation occasions a loss of nitrogen; in the presence of 

 nitrates the difficulties of combustion are great and as yet insuperable; 

 finally, the combustion process cannot be considered as " determining" 

 the carbon and nitrogen of the organic matter in water in a sense to 

 justify the claim of " absolute" value for its results which has been de- 

 nied to those of all other methods. 



The special conclusions as to the albuminoid-ammonia process are as 

 follows : In the determination of both " free " and " albuminoid " ammo- 

 nia there is a loss resulting from imperfect condensation of the ammonia 

 during distillation ; when urea is present some ammonia is easily formed 

 by boiling with sodium carbonate, and this vitiates the determination 

 of "free" ammonia; in the distillation with alkaline permanganates 

 the nitrogenous matter sometimes fails to be completely acted upon be- 

 fore the contents of the retort is nearly reduced to dryness, and great 

 uncertainty results ; the value of the results by this process depends 

 more upon watching Wxe progress and rate of evolution of the ammonia 

 than upon determining its total amount. 



The special conclusions as to the permanganate process are : The re- 

 sults obtained by the Tidy method, and by Kubel's modification of the 

 same, differ irregularly, the latter usually giving much higher figures; 

 the results obtained by the Tidy process are liable to variations with 

 the atmospheric temperature prevailing at the time the process is ap- 

 plied; the amount of oxygen consumed cannot be taken as a measure 

 either of the organic carbon or of the total organic matter, though a 

 general resemblance may be traced between strongly marked results, 

 high or low, for the consumption of oxygen on the one hand and inor- 

 ganic carbon (by the combustion process) on the other; the process is 

 capable of giving more valuable information by watching the rate and 

 progress of the oxidation of organic matter present than by any single 

 determination of the absolute amount of oxygen consumed in a given 

 time. [Am. Chem. J., iv, p. 341.) 



