Fig. 23
Temperature recorder. The recorder with the coordinate paper in the lower box with a glass door. A curve representing the temperature difference between the ingoing and outgoing water is directly drawn on the coordinate paper. Above are three resistance boxes, and the switches for electrical connections are at the right. On the top shelf is the galvanometer, and immediately beneath, the plug resistance box for altering the value of certain shunts.
Fig. 24.—Detailed wiring diagram showing all parts of recording apparatus, together with wiring to thermometers complete, including all previous figures.
The whole apparatus is permanently and substantially installed on the north wall of the calorimeter laboratory. A photograph showing the various parts and their installation is given in fig. 23. On the top shelf is seen the galvanometer and on the lower shelf the recorder with its glass door in front and the coordinate paper dropping into the box below. The curve drawn on the coordinate paper is clearly shown. Above the recorder are the resistance-boxes, three in number, the lower one at the left being the resistance S1, the upper one at the left being the resistance S', and the upper one at the right being the resistance Z1. Immediately above the resistance-box Z1 is shown the plug resistance-box which controls on the one hand the resistance r and on the other hand the resistance S, both of which are substantially altered when changing the apparatus to register from the 0° to 4° scale to the 0° to 8° scale. A detailed wiring diagram is given in fig. 24.
TEMPERATURE CONTROL OF THE INGOING AIR.
Fig. 25.—Section of calorimeter walls and part of ventilating air-circuit, showing part of pipes for ingoing air and outgoing air. On the ingoing air-pipe at the right is the lamp for heating the ingoing air. Just above it, H is the quick-throw valve for shutting off the tension equalizer IJ. I is the copper portion of the tension equalizer, while J is the rubber diaphragm; K, the pet-cock for admitting oxygen; F, E, G, the lead pipe conducting the cold water for the ingoing air; and C, the hair-felt insulation. N, N are brass ferules soldered into the copper and zinc walls through which air-pipes pass; M, a rubber stopper for insulating the air-pipe from the calorimeter; O, the thermal junctions for indicating differences of temperature of ingoing and outgoing air and U, the connection to the outside; QQ, exits for the air-pipes from the box in which thermal junctions are placed; P, the dividing plate separating the ingoing and outgoing air; R, the section of piping conducting the air inside the calorimeter; S, a section of piping through which the air passes from the calorimeter; A, a section of the copper wall; Y, a bolt fastening the copper wall to the 2-1/2 inch angle W; B, a portion of zinc wall; C, hair-felt lining of asbestos wall D; T-J, a thermal junction in the walls.
In passing the current of air through the calorimeter, temperature conditions may easily be such that the air entering is warmer than the outcoming air, in which case heat will be imparted to the calorimeter, or the reverse conditions may obtain and then heat will be brought away. To avoid this difficulty, arrangements are made for arbitrarily controlling the temperature of the air as it enters the calorimeter. This temperature control is based upon the fact that the air leaving the chamber is caused to pass over the ends of a series of thermal junctions shown as O in fig. 25. These thermal junctions have one terminal in the outgoing air and the other in the ingoing air, and consequently any difference in the temperature of the two air-currents is instantly detected by connecting the circuit with the galvanometer. Formerly the temperature control was made a varying one, by providing for either cooling or heating the ingoing air as the situation called for. The heating was done by passing the current through an electric lamp placed in the cross immediately below the tension equalizer J. Cooling was effected by means of a current of water through the lead pipe E closely wrapped around the air-pipe, water entering at F and leaving at G. This lead pipe is insulated by hair-felt pipe-covering, C. More recently, we have adopted the procedure of passing a continuous current of water, usually at a very slow rate, through the lead pipe E and always heating the air somewhat by means of the lamp, the exact temperature control being obtained by varying the heating effect of the lamp itself. This has been found much more satisfactory than by alternating from the cooling system to the heating system. In the case of the air-current, however, it is unnecessary to have the drop-sight feed-valve as used for the wall control, shown in fig. 13.