8 



Proceedings of the Royal Irish Academy, 



Method of Experimenting . 



The method of experimenting, and the special apparatus which 

 have heen employed for the experiments, require but brief reference, 

 as both have been fully described in a memoir on " The Course and 

 IN'ature of Fermentative Changes in JS'atural and Polluted "Waters," 

 published in the Trans. Eoyal Dublin Society, vol. v., ser. 2, 1895. 



Solutions of urea and of the necessary inorganic salts were made up 

 to a convenient strength with fresh distilled water. The dissolved 

 gases, inorganic and organic nitrogen, were determined both at the 

 commencement and at the conclusion of an experiment. 



If the initial or earlier steps only of the fermentation were required 

 to be studied, the solutions were preserved in bottles completely filled 

 and carefully stoppered with well- ground glass stoppers, the dissolved 

 oxygen in the solution providing a sufficient quantity of that gas for 

 the purpose. If, however, it were desired to study the course of 

 fermentation more completely, then it was found necessary to leave 

 air in the bottle sufficient to provide an adequate supply of oxygen. 



It was possible to make the solutions sufficiently dilute to ensure 

 that the dissolved oxygen should be more than sufficient for the com- 

 plete fermentation of the organic substance it contained ; the quantities, 

 however, of substance fennented, and of products formed, would then 

 necessarily be very small — undesirably so for many purposes. 



For the first-mentioned object a bottle of ordinary form is employed ; 

 for the second, one of special form is necessary. I have found Chancel's 

 form of glass flask for taking the specific gravities of gases very 

 convenient for the pui-pose. It consists of a flask, the neck of which 

 is ground and fitted with a hollow glass stopper. A side tubule is 

 fused on the outside of the neck ; and a hole is bored through the side 

 of the stopper to correspond with it. A tube is also fused on the inside 

 of the stopper over the hole ; and by its means, in one position of the 

 stopper, the outer tubule may be placed in direct communication with 

 the interior and bottom portion of the flask. The outer end of the 

 stopper is continued into a glass tube furnished with a stopcock. 

 "With this form of flask, the gases in the air-space, at the conclusion of 

 the experiment, may be easily displaced by means of paraffin oil, 

 and transferred to the special gas analysis apparatus for measurement 

 and analysis {loe. cit., p. 546). The solution may then be displaced and 

 transferred to the laboratory flask of the same apparatus, and the 

 dissolved gases in it boiled out and analysed. 



