The elements of the science of nutrition / by Graham Lusk.

  • Graham Lusk
Date:
1917
Catalogue details

Licence: In copyright

Credit: The elements of the science of nutrition / by Graham Lusk. Source: Wellcome Collection.

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    determined. For example, if the difference between the temperature of the ingoing and outgoing water is 2.50 degrees, and 20 liters of water have passed through the heat absorber in one hour, then 50 calories of heat have been carried away from the apparatus duling the period. If the temperature of the walls within the apparatus has undergone a change this value is subject to corrections, but otherwise the total heat elimination of the person is measured by the 50 calories so determined plus the heat value of water vaporized during the hour. < To obtain an even flow of water through the heat-absorber the water is supplied from a constant-level tank placed above the calorimeter. To obtain ingoing water of an even temperature Williams passed the previously ice-cooled water current through a Gouy temperature regulator and then through a current regulator designed by him- self. These improvements allow the ingoing water to enter the calorimeter at a tem- perature which may not vary more than 0.02° C. during hours of experimentation and, for the first time, permit the exact measurement of small quantities of heat m this type of apparatus. The temperatures of the ingoing and outgoing water are taken every four minutes by electric resistance thermometers and are read in connection with a galvanometer and Kohlrausch bridge on an observer’s table. The quantity of the water-flow is determined by weighing; the water is diverted at the call of “time, so that the exact quantity for the hour is collected in a previously weighed receptacle. Having learned how the heat produced within the apparatus is carried away, the problem of how to prevent loss of heat through the walls of the chamber remains to be discussed. This was accomplished through a device introduced by Rosa. The calor- imeter is constructed of three walls, an inner copper wall which has already been described as the lining of the respiration chamber, an outer copper wall separated from the inner wall by a space of dead air, and an insulating wall (made of two layers of “compo-board,” the space between them being filled with cork), which insulating wall is separated from the outer copper wall by a second space containing dead air. It is obvious that if the inner and outer copper walls of the calorimeter have the same tem- perature there will be no exchange of heat between them. Therefore, to prevent a gain or loss of heat by the inner wall, it is necessary to maintain the outer wall always at exactly the same temperature as the inner wall, under which circumstances the latter cannot gain or lose heat to its neighbor. In order to detect differences in temperature between the outer and inner walls Rosa arranged thermo-couples in series between the two walls. In this fashion the top, sides, and bottom of the box are successively tested every four minutes by an operator It the observer’s table to determine whether there is any difference in tem- perature between the outer and inner walls. If the outer wall is found to have a different temperature from the inner wall, its temperature is brought to that of the inner wall by the following device: A cooling current of water runs through pipes between the insulating and outer copper wall, and in this same space, along the line of the pipes, run “Therlo” resistance wires carrying an electric current for the warming of this interspace (see Fig. 4)* Ry varying the intensity of the electric currents which severally supply the spaces to top, sides and bottom, the temperature of these spaces can be so controlled as to heat or cool the outer copper wall and maintain it at exactly the same temperature as the inner copper wall. This is the effective system which prevents a loss or gain of heat through the wall of the calorimeter. Resistance thermometers are attached to the inner walls of the calorimeter, and if the temperature of the walls rises or falls between the beginning and end of the experi- ment, a correction must be made. It has been found that 19 calories are absorbed by the Sage calorimeter when the inner wall rises 1 degree. Conversely, 19 calories are given up by a fall of 1 degree. I his is the hydrolhct Dial equivalent of the box.