Chemical Analysis of Potable Waters. 



have proposed particular methods for the application of this test, tl 

 most in use at the present time being Tidy's modification which cc 

 sists in the addition of a definite amount of permanganate soluti 

 to a certain quantity of the water acidified with sulphuric acid, 

 the end of a certain length of time the amount of permanganate 

 remaining is determined and the amount of oxygen consumed is ca 

 culated and reported as "oxygen absorbed." Very generally, tw 

 determinations are made on different samples of the water, the pei 

 manganate being allowed to act for fifteen minutes in one case and 

 for three or four hours in the other. 



Tidy and his adherents attach great importance to the results thus 

 obtained. Frankland admits that they are not without value, and finds 

 that thev corresponded in 1418 out of 1686 cases quite closely with 

 those obtained by his own very elaborate method presently to be de- 

 scribed. Wanklyn condemns the method as misleading on account of 

 want of delicacy and the fact that albumen is not readily attacked by 

 the standard solution of permanganate, while, as Frankland long ago 

 pointed out, such bodies as starch and cane sugar take up less than the 

 one-hundredth part of the oxygen required for total oxidation. The 

 majority of water analysts probably realize the imperfections of all 

 permanganate methods, but consider their indications as not without 

 a certain value. In this connection it may be remarked that Wanklyn 

 has proposed and patented a method known as the " moist combustion 

 process," in which an alkaline solution of permanganate is distilled 

 with the water and the amount of permanganate consumed deter- 

 mined. It has not been received with much favor. 



2. Wanklyn and Chapman's albumenoid-ammonia process. - The 

 ammonia method so well known and largely employed at the 

 present time was brought forward by Wanklyn, Chapman and Smith 

 in 1867. The modified process now in general use is described m the 

 fifth edition of Wanklyn and Chapman's Water Analysis. Ao method 

 ng analysts, a fact, perhaps 

 th which the test is applied, 



iver found such general favor among analy 



nicety of the process 



„_ nd the seeming accuracy cer- 

 tainly delicacv — of the method. Nevertheless it has been narshly 

 criticised by many and especially by Frankland and his followers. 



In this test a definite quantity of water is boiled in a retort, some car- 

 bonate of sodium having been added if necessary to render the water al- 

 kaline, and the ammonia which existed as such in the water or has re- 

 sulted from the decomposition of urea and like substances, passes over 

 with the escaping steam which is condensed and the amount deter- 

 mined with Nessler's solution and reported as " free ammonia. When 

 this has all been given off an alkaline solution of permanganate of 



