Y.. Henderson 83 
the fatiguing elevations of the mercury bulb. In use the pyro- 
gallate solution is covered with a layer of petroleum oil sufficiently 
deep to protect it from the outside air. The lower ends of the 
pieces of glass tubing in the pyrogallate must be cut or broken 
diagonally. ‘The control tube*may be directly back of the gas 
burette instead of to one side as in the figure. 
It will be noticed that the water jacket enclosing the gas burette and 
the control tube has been shortened so as to include little more than the 
Frea2. 
bulbs and upper parts. This is allowable because the object of the water 
jacket is not to keep the temperature constant but to make it possible by 
stirring or bubbling the water to bring the air in the two bulbs to the same 
temperature and water vapor tension at the time of an observation. It is 
extremely hard on the eyes to read a fine burette accurately through the 
glass and water of a long jacket. A small ‘magnifying glass arranged to 
slide on the tube of the gas burette is convenient.? In all other re- 
spects the apparatus, the technique, and precautions on itg use are the 
* Wm. Gaertner and Company, 5345 Lake Park Avenue, Chicago, make a 
convenient form (Catalog No. C1365). 
THE JOURNAL OF BIOLOGICAL CHEMISTRY, VOL. < XXIII, NO. 1 
