An Indirect Calorimeter for the Determination of O 2 and CO 2.

Abstract

The essential parts of the calorimeter are: (a) a tank containing about 300 litres of water; (b) 2 cylindrical spirometer domes in the tank, the capacity of each being 100 litres and height 1 meter; (c) a tank containing 5 kilos of 4 mesh soda lime connected with each spirometer with a 3-way valve; (d) a glass tube of 2.5 cm. bore shaped like the Greek letter π, one end of the horizontal portion being the mouth piece, the other closed by a rubber stopper at the moment the experiment is to begin, and the 2 vertical portions fitted with 4 cm. lengths of Visking sausage casings (to act as valves) and connected by rubber tubing to the 3-way valves. Each spirometer dome is counterbalanced by a weight fastened to a bicycle chain passing over a large bicycle sprocket wheel. The thickness of the wall of the dome is such that the weight of water displaced equals the weight of the chain. A meter stick is used as a scale and each mm. corresponds to 100 cc. A thermometer is inserted in each spirometer dome. The tube leading from the 3-way valve up through the water into the spirometer has a large enough surface to bring the air passing through it to the temperature of the water and this tube in spirometer No. 1 contains a wick to saturate the air with moisture.

In operation, spirometer No. 1 is filled with outdoor air (the CO₂ of which is considered negligible), the temperature recorded and spirometer No. 2 left empty, the mouthpiece adjusted to the patient and the breathing watched. At the end of an expiration the rubber stopper is inserted and stop watch started.