Recent Progress in Sanitary Science. 281 



— and it is to these that we must chiefly look in deciding 

 upon their fitness for domestic uses — it may be briefly said 

 that they are four in number — the "ignition," "permangan- 

 ate," "albuminoid ammonia," and "combustion" methods. 

 The first is no longer regarded as adequate to give the infor- 

 mation needed ; the second is deemed fallacious ; and the 

 third, although still employed by many chemists, will, for 

 similar reasons, have to be abandoned. The fourth gives the 

 information required, with an accuracy adequate to the form- 

 ation of correct judgment on the water analyzed, but at 

 present has the disadvantage of requiring much time and 

 care in its satisfactory performance. 



It should be said here, in justice to the chemists who still 

 employ the "albuminoid ammonia" process, that they do not 

 claim that the albuminoid matters give up all their nitrogen 

 in the form of ammonia, but only that they yield by this pro- 

 cess a certain measure, and that this measure can be used as 

 an index of the amount of the organic impurity present. 

 But, as was shown by the authors themselves, and as has been 

 since still more satisfactorily demonstrated, water containing 

 known quantities of organic matter, when treated by this 

 process, yields an amount of nitrogen which differs accord- 

 ing to the character of the substances operated upon. It is 

 evident that if the process were good, it should indicate 

 either the whole amount of nitrogen present, or in every 

 case, a definite proportion of it ; and in failing, as it does, 

 to meet these requirements, the albuminoid ammonia method 

 of determining the organic impurity must be condemned. 

 This failure is strikingly exemplified in the case of urea, per- 

 haps the most characteristic ingredient of sewage, which may 

 be present in a drinking water without detection by the al- 

 buminoid ammonia process. On the other hand, peaty mat- 

 ters, which color the water without rendering it noxious, 

 yield a large amount of albuminoid ammonia, and such 

 waters have in this wise been in some cases unfairly con- 

 demned. 



