Human Calorimetry

Abstract

A respiration calorimeter is described in which the measurement of direct heat has many automatic features. The respiration chamber is a cylinder of Pyrex glass through which air circulates in a closed circuit including two interchangeable Benedict trains of absorbers. Oxygen is admitted automatically as it is consumed and is measured on a wet test meter. Cold waterbrought initially to a constant temperaturepasses through a grid of pyrex tubes to carry away most of the heat. The temperatures of inflowing and outflowing water and air, and the temperature of the glass wall are electrically measured and automatically recorded every minute. Water flow and air flow are recorded by meters of special design. The calorimeter is not adiabatic, the escape of heat through the insulation around the walls being measured by the thermal gradient set up across it, which is electrically recorded by resistance thermometers. Calibration with electrical input of heat gives the heat flow for a given gradient and also the hydrothermal equivalent (22.1 Calories per degree). In a series of alcohol checks, the totals of direct and indirect heats differ by 0.17 per cent, while the average difference in individual hour periods is 2.9 per cent. In human calorimetry, the average difference is morebut by the use of rectal and surface temperatures measured by resistance thermometers, it has been brought to 5.5 per cent.