Efficiency of carbon dioxide absorption by soda lime in a closed system.

The efficiency of the carbon dioxide absorption by soda lime was determined in the following way. (1) " Circle " breathing. In six experiments, a subject breathing through a Waters canister fully packed with 425 g of fresh soda lime was connected to a closed circuit spirometer as described by Erikson et al. (1951). The expired air then passed the canister before entering the spirometer where the amount of carbon dioxide not absorbed by the soda lime was determined. This was achieved by circulating the expired air through an absorption unit with 10 per cent KOH. In this unit, where temperature and vapour pressure are constant, carbon dioxide was completely removed and recorded volumetrically with an accuracy of ± 5 ml. The inspired air was also drawn through the canister. The ventilation and oxygen consumption of the subjects were simultaneously determined. The resistance of the spirometer is negligible, only 2 to 3 mm of water. The carbon dioxide absorption in two different brands of widely used soda lime was compared. Both these brands were from manufacturers of high reputation and filled the requirements set for soda lime for anaesthetic purposes. The regeneration of the activity of the soda lime was investigated in some experiments, inserting " resting periods " of 40 minutes several times during the experiments (in one case the "resting period " was 24 hours). In one experiment the absorbing efficiency during increased metabolism due to exercise (250 kg-m/min on a bicycle ergometer) was determined. (2) " To and fro " breathing. In two experiments the efficiency of carbon dioxide absorption in a "to and fro " breathing system was determined by analysing the carbon dioxide content in samples of inhaled air using an experimental arrangement as shown in figure 1. Oxygen was supplied continuously in order to maintain a convenient volume of