112 VITALITY AND EFFICIENCY WITH RESTRICTED DIET. 



to actuate a second by-pass on the blower, which is controlled by an 

 electrical magnet. 



This by-pass is constructed in the following manner: The pipes on 

 each side of the by-pass, h and /12 (fig. H), are extended and reduced in 

 size to permit the insertion of a short length of thin-walled soft rubber 

 tubing, mi and 7^2. By placing this tubing back of the armature of a 

 small magnet (an inexpensive telegraph sounder has been found suit- 

 able for the purpose), air may be allowed to pass at will through the 

 rubber tube by opening or closing the magnet. A vertical movement 

 of the rubber diaphragm of 1 mm. opens or closes a simple electrical 

 contact which is actuated by two small disks {di and d2, figure 13) on 

 the suspension rod of the diaphragm on each sampling can. This in 

 turn opens or closes the magnet release and hence leaves the passage 

 free or obstructed through the rubber tube of the by-pass mi or m2. 

 The details are shown in figures 11 and 13. 



With this arrangement, if the blower draws somewhat too much air out 

 of the sampling can, i. e., more than is delivered to it, the diaphragm 

 tends to fall; this closes the electric contact which, in turn, draws down 

 the telegraph sounder. The normal spring tension against the rubber 

 tube mi or m2 is released by this movement, thus allowing air free 

 passage through the tube. Under these conditions the blower draws 

 too little air from the can and the discharge from the wind chest is 

 somewhat greater than its removal from the sampling can. This 

 results in a slight raising of the rubber diaphragm, the breaking of the 

 electric contact, and the closing of the by-pass mi and m2. This alter- 

 nate opening and closing is practically continuous, occurring several 

 times each second. Under these conditions the position of the rubber 

 diaphragm remains nearly constant and the pressure of the air inside 

 the sampling chamber is atmospheric. 



This constancy in atmospheric pressure may be tested by an ex- 

 tremely delicate Sond^n petroleum manometer P (fig. 8), which is so 

 mounted that, by turning a 3-way stopcock, it can be connected with 

 either of the sampling cans at will. If the pressure inside the sam- 

 pling can is atmospheric, the petroleum manometer indicates 0. The 

 adjustment at the start is easily made by increasing or decreasing the 

 tension on the spiral springs above the rubber diaphragm by means of 

 the small regulating nuts, ni and n2. 



If the manometer shows that the pressure is too great inside the can, 

 the weight of the diaphragm has not been suitably counterpoised; 

 hence it is necessary to turn the nut so as to produce greater tension on 

 the spring. When the pressure inside is below atmospheric, the opera- 

 tion is reversed. The small disks which actuate the electric magnet 

 are attached to the vertical rod by tiny set screws and can be adjusted 

 for any elevation. When once adjusted, however, very considerable 



