56 CALORIMETERS FOR STUDYING RESPIRATORY EXCHANGE, ETC. 



closed and sealed by hot wax and rarely is a leakage experienced. The trap- 

 door is constructed on precisely the same plan as the rest of the calorim- 

 eter, having its double walls of copper and zinc, its thermal-junction system, 

 its heating wires and connections, and its cooling pipes. When closed and 

 sealed, and the connections made with the cooling pipes and heating wires, 

 it presents an appearance not differing from any other portion of the 

 calorimeter. 



The next largest opening is the food-aperture, which is a large sheet- 

 copper tube, somewhat flattened, thus giving a slightly oval form, closed 

 with a port, such as is used on vessels. The door of the port consists of 

 a heavy brass frame with a heavy glass window and it can be closed tightly 

 by means of a rubber gasket and two thumbscrews. On the outside is used 

 a similar port provided with a tube somewhat larger in diameter than that 

 connected with the inner port. The annular space between these tubes is 

 filled with a pneumatic gasket which can be inflated and thus a tight closure 

 may be maintained. When one door is closed and the other opened, articles 

 can be placed in and taken out of the chamber without the passage of a 

 material amount of air from the chamber to the room outside or into the 

 chamber from outside. 



The air-pipes passing through the wall of the calorimeter are of standard 

 1-inch piping. The insulation from the copper wall is made by a rubber 

 stopper through which this piping is passed, the stopper being crowded 

 into a brass ferule which is stoutly soldered to the copper wall. This is 

 shown in detail in fig. 25, in which N" is the brass ferule and M the rubber 

 stopper through which the air-pipe passes. The closure is absolutely air- 

 tight and a minimum amount of heat is conducted out of the chamber, 

 owing to the insulation of the rubber stopper M. The water-current enters 

 and leaves the chamber through two pipes insulated in two similar brass 

 ferules soldered to the copper and zinc walls. The insulation between the 

 water-pipe and the brass ferule has been the subject of much experimenting 

 and is discussed on page 24. The best insulation was secured by a vacuum- 

 jacketed glass tube, although the special hard-rubber tubes surrounding the 

 electric-resistance thermometers have proven very effective as insulators in 

 the bed calorimeter. 



A series of small brass tubes, from 10 to 15 millimeters in diameter, are 

 soldered into the copper wall in the vicinity of the water-pipes. These are 

 used for electrical connections and for connections with the manometer, 

 stethoscope, and pneumograph. All of these openings are tested carefully 

 and shown to be absolutely air-tight before being put in use. 



In the dome of the calorimeter, and directly over the head of the subject, 

 is the opening for the weighing apparatus. This consists of a hard-rubber 

 tube, threaded at one end and screwed into a brass flange heavily soldered 

 to the copper wall (fig. 9). When not in use, a solid rubber stopper on a 



