I 



CHEMICAL ANALYSIS 37 



manganate at once, distilling and Nesslerizing, then deducting 

 the free and saline ammonia obtained by direct titration, re- 

 cording the difference as '' albuminoid NH3." In this way 

 more ammonia is obtained, but the results are not comparable 

 with published analyses, and in effluents are more unfavourable 

 when referred to the limits laid down by various Boards ; there- 

 fore it seems best to keep to the older conventional method as 

 originally laid down by Wanklyn. We shall have to refer 

 again to the standards officially prescribed. To show the great 

 variation, I have found the free ammonia in ordinary raw 

 sewages to range from 35 to less than i per 100,000, and the 

 albuminoid from 6 to o*i per 100,000, the latter, of course, 

 being largely subsoil or rain-water. 



Oxygen Consumed. — This test has been variously called the 

 *' oxygen absorbed figure," the ** oxygen test," or simply the 

 "permanganate test." While in the ordinary "albuminoid" 

 method permanganate is used in a strongly alkaline solution, 

 and only the ammonia evolved is measured, in this process the 

 permanganate solution is acidified with sulphuric acid, digested 

 with the water or sewage, and after a certain time the amount 

 of permanganate remaining is determined volumetrically. The 

 original quantity of permanganate added being known, the loss 

 indicates the oxygen which has been absorbed by the organic 

 matter and other oxidizable bodies present. 



This process, originally devised by Forschammer about 1865, 

 was subsequently improved by Letheby and Tidy, and has 

 attained importance as a standard comparative method on 

 account of the ease and rapidity of its performance. 



Opinions have in many cases been founded almost solely on 

 the permanganate process of oxidation ; but such a proceeding 

 is to be condemned, as, although decidedly valuable, the test 

 is open to the following objections : 



1. So many modifications have been introduced in procedure 

 that the figures obtained by various observers are seldom com- 

 parable. 



2. It mainly measures the carbonaceous matters, which are 

 not the most dangerous. 



3. It is incomplete even in measuring these, since it has been 

 found on trials with various definite organic matters that they 

 varied greatly in their reducing power, and some of them were 

 very resistant to permanganate when used, according to the 

 ordinary prescription, at low temperatures. For this reason, in 



