110 VITALITY AND EFFICIENCY WITH RESTRICTED DIET. 



ling can as rapidly as it was introduced, the air as supplied from the 

 wind chest being under only slight positive pressure, amounting to but 

 a few millimeters of water. It thus became necessary to adjust the 

 receiving chamber so that the pressure of air inside was always atmos- 

 pheric. 



To do this the receiving chambers or sampling cans into which the 

 small orifices opened were made as follows: A copper can was used, 

 which was provided with a cover consisting of a lady's bathing cap, 

 made of pure gum, securely fastened around the edges. The greater 

 part of the weight of this rubber top was borne by a light aluminum 

 disk placed inside the cap. To the disk was fastened an upright brass 

 rod with tight closure about the rod. At the top of this brass rod a hook 

 was attached to a slight spiral spring suspended from a standard. 

 The combined weight of the rod, disk, and rubber cap was thus borne 

 by the spring. Without this suspension effect the weight of the rubber 

 would increase the pressure. With the suspension effect the bag was 

 held in position so that at any one moment there would be complete 

 atmospheric pressure if provision were made to remove the air as 

 soon as it was delivered into the can. 



The details of these diaphragms and their suspension and electrical 

 connections are given in figure 13, which shows their normal position 

 when the ventilating air-circuit is not in action, ^. e., when counter- 

 poised by means of the delicate spiral springs, Si and S2, at the top. 

 The tension on the springs can be easily adjusted by the nuts rii and ^2 

 and thread on the ends of the suspension hooks. The air coming from 

 the wind chest is thus discharged into a chamber, which, though pro- 

 vided with a flexible top, is nevertheless absolutely air-tight. Since it 

 is necessary in many preliminary adjustments of the apparatus to have 

 a free opening from each of the cans into the air, aside from that leading 

 to the blower, a small piece of brass tubing is soldered into the side of 

 each can at 61 and 62. When the apparatus is running, the two pipes 

 are easily closed by inserting solid rubber stoppers. 



If the air is removed from this chamber more rapidly than it is 

 delivered, there will be diminished pressure inside the rubber dia- 

 phragm, thus puUing down on the spring from which it is suspended. 

 The ultimate result will be a slightly decreased pressure above the open- 

 ing leading into the wind chest. If , on the contrary, the air is withdrawn 

 more slowly than it is delivered, the rubber diaphragm over the can 

 will distend, raise the aluminum disk, lessen the work of the spring, and 

 produce a slight positive pressure at the orifice into the wind chest. 

 Thus, while air will be delivered free into the room from the large open- 

 ing, it will be compressed in the rubber diaphragm over the sampling 

 can. It is therefore necessary to remove the air from the sampling can 

 at the same rate that it is deHvered in order that atmospheric pressure 

 may be maintained. 



