Adeney — Dissolved Gases and Fermentative Changes. 549 



for air to diffuse through the indiarubber tube. With this arrangement, if an 

 appreciable quantity of air does thus diffuse during an experiment, it passes up 

 into the pressure-tube when the reservoir is raised, and can be driven out when 

 necessary through the stopcock at its upper extremity, without in any way 

 affecting the experiment ; as a precaution against the air being carried round into 

 the burette by the inflowing mercury, the pressure-tube is expanded considerably 

 where the side tube is attached to it, as shown in the drawing. 



The upper end of the burette is provided with a Friedrich's patent two-way 

 stop-cock, by means of which communication with the laboratory flask, or a 

 laboratory vessel, to which it is connected by the branch tubes shown in the 

 drawing, can be opened or closed at will. 



The upper branch tube leading to the condenser and flask is 3 mm. bore ; the 

 lower branch is a capillary tube. 



The two branch tubes are held against a wooden block, shown in the drawing, 

 in cork-lined grooves, by a brass jjlate, also cork-lined, and screwed to the block. 

 The grooves are made sufficient in width to allow of considerable play in a vertical 

 direction. 



This last precaution is necessary to allow for alteration in length of the burette 

 induced by changes of temperature. When the tubes are properly fitted in these 

 grooves, there is no danger whatever of their being broken, even if the apparatus 

 is subjected to careless handling. 



The contracted portion of the upper part of the burette is about 225 mm. long, 

 and has a capacity of 15 c.cs., the wider portion being about 410 mm. long, with 

 a capacity of somewhat more than 250 ccs. Both portions are graduated, the 

 former at intervals of one-tenth c.c, and the latter at intervals of 25 c.cs. 



The pressure-tube has a working length of 1000 mm. above the level of the 

 lowest division, viz. the 250 c.cs. line of the burette. 



The height of the mercury in the pressure-tube is read by means of a 

 millimetre scale etched on the unsilvered surface of a narrow slip of looking-glass, 

 which is fixed to the back of the apparatus, close to the pressure-tube, at such an 

 angle as to reflect the image of the tube through the portion of the glass bearing 

 the scale. To read the height of the mercury in the tube, the eye is held a little 

 to the right of the scale, and moved about until the scale-lines in the immediate 

 vicinity of the reflected image of the mercury meniscus coincide with their own 

 images reflected from the silvered surface of the glass. When the eye is in this 

 position, the height of the mercury in the tube can be accurately read to 0.5 mm. 

 The laboratory vessel differs in principle and shape from that used in 

 Frankland's and M'Cleod's apparatus. Its shape is shown in the drawing ; the 

 lower end, which is cylindrical in shape, is 25 mm. diameter, and 55 mm. long, 

 and is furnished with a side tube for connecting the vessel with a separate 



412 



