546 Adeney — Dissolved Gases and Fermentative Changes. 



fermentation of various fermentable matters under gradually varying condition 

 from that in which the fermentable matters were in excess to that in which the 

 dissolved oxygen was in excess. 



One further general condition which had to be attended to in all the 

 experiments need scarcely be mentioned : it was to make provision for keeping the 

 liquids under observation in a slightly alkaline condition during fermentation. 

 This was invariably done by adding, when necessary, very small quantities of 

 pure dry sodium carbonate, which consisted partly of the normal carbonate and 

 partly of the bicarbonate. When experimenting with sewage-water, it was found 

 to be quite unnecessary to add any of this or other mineral substances. All the 

 solutions were kept in the dark during fermentation. 



Apparatus Employed. 



The bottles I have employed for preserving the waters or solutions under 

 experiment, out of contact with air, have been made in two forms : one, the 

 ordinary bottle-form with short necks ; the other of flask form, with long, some- 

 what narrow necks. Both forms have been made of stout glass with very 

 carefully ground stoppers. The capacity of the bottles has varied, according to 

 circumstances, from about 300 c. cs. to 2500 c.cs. 



As before stated, the bottles, when filled, were carefully stoppered so as to 

 leave not a trace of air bubble in them. To avoid the possibility of small 

 quantities of air passing into them between the neck and the stopper, they have 

 been kept neck downwards immersed in distilled water. Under these circum- 

 stances, a little distilled water might be drawn into the bottles, or a little solution 

 expelled from them, but not in sufficient quantity to introduce material error, 

 provided the temperature of their contents was not allowed to vary much. When, 

 from any cause, such as considerable variation of temperature, or the formation 

 of gaseous products, other than carbon dioxide, during fermentation, disengage- 

 ment of gas during the course of an experiment was to be anticipated, such 

 gas would remain in the bottle, since this latter was kept neck downwards, and 

 some liquid would be expelled from it between the neck and the stopper. It 

 would be necessary, of course, to collect this gas, and separately measure and 

 analyse it. To meet this special case, the flask-shaped bottles, with long narrow 

 necks mentioned above, were employed. The neck of each bottle was graduated 

 from the bottom of the stopper downwards, as follows : the bottle was completely 

 filled with water, and the stopper firmly inserted ; the stopper was then carefully 

 taken out, and the height of the water was marked on the neck with a diamond as 

 zero, the graduation was then proceeded with by withdx'awing the water half a 

 cubic centremetre at a time, and marking on the neck the height of the water as 



