GENERAL DESCRIPTION OF RESPIRATION APPARATUS. 63 



its load. By turning a 3-way valve at the end of the compressed-air supply- 

 pipe, so that the air rushes into the cylinder above the piston, the piston 

 is pushed to the base of the cylinder and the elevator thereby raised. The 

 pressure of the compressed air holds the elevator in this position while the 

 hooks are being adjusted on the absorber. By turning the 3-way valve so 

 as to open the exhaust leading to the upper part of the cylinder to the air, 

 the weight of the elevator expels the air, and it soon settles into the posi- 

 tion shown in the figure. The weighing can then be made as the absorber 

 is swinging freely in the air. After the weighing has been made, the ele- 

 vator is again lifted, the hooks are released, and by turning the valve the 

 elevator and load are safely lowered. 



The size of the openings of the pipes into the cylinder is so adjusted that 

 the movement of the elevator is regular and moderate whether it is being 

 raised or lowered, thus avoiding any sudden jars that might cause an 

 accident to the absorbers. With this system it is possible to weigh these 

 absorbers to within 0.1 gram and, were it necessary, probably the error 

 could be diminished so that the weight could be taken to 0.05 gram. On 

 a balance of this type described elsewhere,* weighings could be obtained to 

 within 0.02 gram. For all practical purposes, however, we do not use the 

 balance for weighing the absorbers closer than to within 0.10 gram. In 

 attempting to secure accuracy no greater than this, it is unnecessary to 

 lower the glass door to the balance case or, indeed, to close the two doors to 

 the compartment in which the elevator is closed, as the slight air-currents 

 do not affect the accuracy of the weighing when only 0.1 gram sensitiveness 

 is required. 



PURIFICATION OF THE AIR-CURRENT WITH SODIUM BICARBONATE. 



As is to be expected, the passage of so large a volume of air through the 

 sulphuric acid in such a relatively small space results in a slight acid odor 

 in the air-current leaving this absorber. The amount of material thus 

 leaving the absorber is not weighable, as has been shown by repeated tests, 

 but nevertheless there is a sufficiently irritating acid odor to make the air 

 very uncomfortable for subsequent respiration. It has been found that this 

 odor can be wholly eliminated by passing the air through a can containing 

 cotton wool and dry sodium bicarbonate. This can is not weighed, and 

 indeed, after days of use, there is no appreciable change in its weight. 



VALVES. 



In order to subdivide experiments into periods as short as 1 or 2 hours, 

 it is necessary to deflect the air-current at the end of each period from one 

 set of purifiers to the other, in order to weigh the set used and to measure 



* W. O. Atwater and F. G. Benedict: A respiration calorimeter with appliances 

 for the direct determination of oxygen. Carnegie Institution of Washington 

 Publication No. 42, p. 56. (1905.) 



