Fig. 4. Halothane 2.5% (top ) and 5% (bottom ) in 2 l/min oxygen flowing through dry soda lime; legend corresponds to figure 1, scaling differs from figures 1–3. Range of carbon monoxide (CO) concentration (left ordinate) is reduced from 2 to 1% (0.1%= 1,000 ppm); temperature (right ordinate) is increased to 200°C. CO formation starts gradually at the time the temperature increases and ceases when temperature reaches the upper layer of the soda lime.