Adeney — Dissolved Gases and Fermentative Changes. 551 



groove cut in the wooden back of the apparatus, so that, thus guided, it can be 

 moved up and down in a vertical direction, and clamped at any point by a thumb- 

 screw, so as to adjust the amount of pressure which the upper end of the 

 laboratory vessel will exercise on the rubber collar. 



This adjustment provides for all alteration, either in the length of the 

 laboratory vessel, owing to changes of temperature, or in the size of the rubber 

 cork, owing to wear or replacement, and ensures an air-tight joint with the 

 capillary tube from the burette at all times. 



The whole apparatus is supported on a strongly-made table, 91 ctms. high. 



The method of working the apparatus is as follows : — The pressure-tube, 

 burette and laboratory vessel being filled with mercury, and all stopcocks closed, 

 the laboratory vessel is placed in its position in the manner just described. The 

 laboratory flask, into which 50 c.cs. of pure distilled water have been placed, with 

 or without the addition of 1 or 2 c.cs. of pure sulphuric acid, as the experiment 

 may require, has been placed, is* fitted to the end of the condenser. The water in 

 the flask is then boiled, the air and steam escaping through the side tube in the 

 neck of the flask. The end of this tube is fitted with a short piece of indiarubber 

 tubing. After continuing the boiling for about ten or fifteen minutes, the burner 

 is removed from under the flask, and at the same time the short rubber tube, 

 attached to the side tube from the neck, is closed with a piece of glass rod. 



By this operation the flask is largely freed from air; the aii* still remaining in 

 it, and in the condensing tube is next drawn off by working the apparatus as an 

 air-pump. This is done by lowering the burette reservoir to its lowest limit, the 

 mercury flowing out of the burette, leaving it in vacuo. If now the stopcock 

 of the burette be turned to open communication between it and the laboratory 

 flask, aqueous vapour and portions of the residuum of air left in the flask will 

 pass into the burette. The stopcock is then turned to close communication with 

 the laboratory flask, and the reservoir raised to refill the burette with mercury. 

 The air and water drawn into the burette by this operation are then passed into 

 the laboratory vessel by opening communication therewith. By this time the 

 neck of the flask and the side tube therefrom will be sufficiently cooled to allow 

 of water being safely poured into the space left in the neck above the rubber 

 cork, by which the condensing tube is fitted into the flask, to protect it 

 from the air, and to fit a water-jacket over the piece of rubber tubing closing 

 the side tube. 



The operation of drawing aqueous vapour and gases from the laboratory flask 

 into the burette, and driving them thence into the laboratory vessel is repeated 

 until the mercury, or rather the condensed water on the top of the mercury, 

 strikes the closed stopcock of the burette with a sharp metallic click when the 

 burette becomes full of mercury. In this way the burette provides an extremely 



