Adeney — Dissolved Gases and Fermentative Changes. 545 



spheric oxygen proceeding in the portions of the liquid immediately adjoining 

 the surface exposed to the air in the vessel in which it was kept, and at the 

 same time a fermentation in the practically complete absence of dissolved oxygen 

 in the lower portions of the liquid. The only possible way of ensuring the third 

 condition above stated, was to keep the water or liquid under observation in bottles 

 completely filled and carefully closed with glass stoppers. The difiiculties to 

 be anticipated in practically carrying this out were those which would certainly 

 arise with unavoidable alterations of the temperature of the liquid during the 

 continuance of the experiment. With fall of temperature, there would be a 

 tendency to draw air into the bottle, and with a rise there would be a tendency 

 to expel a portion of the liquid from it, while with both rise and fall of tempera- 

 ture, there might be a disengagement, and possibly, in consequence, a loss of 

 dissolved gases. 



I found, however, that by keeping the bottles immersed, neck downwards, in 

 distilled water, in large glass vessels which were covered with glass plates, and 

 by exposing them to a temperature as equable as possible, that these difficulties 

 could be overcome to such an extent that they could not give rise to errors 

 sufficiently large to materially affect the results. 



I shall again refer to this subject when dealing generally with the probable 

 errors of the experimental results. 



The foregoing consideration of the third necessary condition to be established 

 in my method of experimenting has, it will be observed, included the first. 

 There remains now for discussion the second condition. 



For the purpose of this Paper it was of chief importance to observe the products 

 of fermentation which had been carried on in the continued presence of an excess 

 of oxygen relatively to the quantity of matter to be fermented. 



It was also of importance to determine whether the complete fermentation, on 

 the one hand, of the nitrogenous organic matters, and, on the other hand, of 

 non-nitrogenous organic matters mixed with ammonium compounds, into carbon 

 dioxide, water, and nitrous or nitric acids, in the continued presence of an excess 

 of oxygen, was complete from the commencement or was progressive. 



To effect these purposes, I adopted the general plan of commencing with 

 strong solutions of sewage-waters, or of fresh peat, or of organic and inorganic 

 substances of known strength and composition, in which the quantities of 

 fermentable matters were in decided excess, relatively, to the quantity of dissolved 

 atmospheric oxygen present, and then of making a series of gradually increasing 

 dilutions with good tap-water, or, when necessary, with distilled water, such that 

 the conditions should gradually become reversed, the dissolved oxygen in the 

 higher dilutions becoming predominant in quantity. By this means I hoped to 

 obtain results which would quantitatively indicate the changes resulting from the 



