ApEnEY—Studies in Chemical Analysis of Fresh & Salt Waters. 347 
pletely fills. This is easily done by keeping the bottle immersed 
in water, neck downwards. 
After keeping for a sufficient time, the dissolved gases and 
inorganic nitrogen compounds are determined as with the first 
portion, and the two sets of results give the means of determining 
quantitatively the changes in composition of the dissolved gases, 
and of the nitrogen compounds, brought about by the fermentative 
processes which the sample has undergone during the time it has 
been kept. 
ADVANTAGE OF THE A#RATION Mrtuop. 
The advantage of the method was shown to be that it gave 
absolute results and not comparative, and determined with very 
great accuracy the amount of fermentable organic matter present 
in the water, in terms of the carbon dioxide, and of the ammonia- 
eal, and (possibly) nitrous and nitric, nitrogen formed, and of the 
dissolved oxygen consumed by their complete aérobic fermentation, 
and that also it enabled a distinction to be drawn between the 
oxygen consumed in the fermentation of the organic matter, and 
that consumed in the fermentation, or nitrification, of the ammonia. 
The value of the method has been recognised by chemists having 
a special knowledge of the subject. It, however, necessitates the 
determination of the dissolved gases in a polluted water, both 
when fresh and after fermentation. This involves, of course, 
gasometric analysis ; and gasometric methods have apparently been 
avoided where possible by analysts in water analysis as being too 
laborious. . 
Attempts have been made to obtain sufficiently definite results 
without the aid of gasometric methods of analysis, but I do not know 
that any of them have been followed with even partial success. 
It was hoped that some definite relationship would be found 
to exist between the actual quantities of organic matters in polluted 
waters, and the “oxygen absorbed’ by them from acid perman- 
ganate, and possibly also the ‘“‘ albuminoid ammonia”? yielded by 
them with alkaline permanganate. Practical attempts, however, 
to establish such relationships have failed to realise this hope. 
The important paper’ recently communicated to this Society by 
Professor Letts, D.Sc., and his pupils, gives some interesting 
1 Scien. Proc. R.D.S., vol. ix. (N.S.), pt. 11., p. 337. 
