1883. 113 Trans. N. V. Ac. Set. 



The amount of silver thus thrown down can be readily weighed, and 

 the relative amounts of organic matter present in the water thus deter- 

 mined. A sample of Brooklyn water, taken Mar. 4th, when the water 

 had deteriorated, showed this fact by the large amount of silver which 

 it precipitated. And during the month of January, when I was called 

 on to Philadelphia to examine their water-supply, at that time very 

 offensive to both smell and taste, this method of examination was ex- 

 tensively used. It showed, among other things, that when sufficient air 

 was passed through the Philadelphia water to raise the percentage of 

 oxygen to the proper amount, the decomposable organic matter was 

 largely destroyed ; and samples thus treated threw down just so much 

 less silver, on exposure to sunlight, as there had been organic matter 

 destroyed by previous oxidation in contact with air. This elucidated 

 the origin of the difficulty with the Philadelphia water. It had not 

 been aerated sufficiently to get rid of the decomposable organic matter 

 which it contained, and which communicated its offensive taste and 

 smell. 



DISCUSSION. 



Mr. a, H. Elliott remarked, in reference to the determination 

 of free ammonia in water by distillation with sodium-carbonate, that 

 albuminoids are decomposed in this way, and that the method 

 is fallacious : since, for example, in the case of urea, ammonia is 

 given off before potassium-permanganate and caustic potassa are 

 added. 



The potassium-permanganate is itself full of ammonia, unless it has 

 been previously purified. 



The methods of Wanklyn and Frankland were brought up in vio- 

 lent controversy at the meetings of the Chemical Society of London. 

 Frankland's method was found to be too cumbrous, and there was 

 nothing to be gained by it, since, like Wanklyn's, it only afforded 

 an index of the organic matter present. The distinction between 

 free and albuminoid ammonia was of little value. 



The connection of the healthfulness of waters with their content 

 of organic matter was but vaguely established, since, for example, 

 that of the Dismal Swamp was dark-colored and teeming with or- 

 ganic matter, and yet was not proved unhealthful. Prof. Huxley 

 could see only one use in the determination of the organic matter, 

 with reference to it as a basis for the development of germs. Prof. 

 Koch had proposed a method of the development of bacteria in 

 gelatine-films, which had not yet apparently been sufficiently tested. 



