524 Experiments 



sures are measured on the axis of the abscissae, in increasing order, 

 and the quantities of oxygen are represented on that of the ordi- 

 nates. We shall see presently that this curve, if we set aside the 



Fig. 17— Composition of confined air which has become lethal at pressures 

 below 1 atmosphere. O. Proportions of oxygen remaining. CO 2 . 

 Proportions of carbonic acid. CO'-f-O. Sum of oxygen consumed 

 and carbonic acid formed. 



little irregularities of which we have spoken, takes a precise geo- 

 metric form, which is exactly a branch of a hyperbola. 



The proportion of carbonic acid produced naturally follows an 

 opposite course, as is shown by curve C0 2 , which represents its 

 modifications. 



Therefore, the weaker the pressure, the less the confined air 

 needs to be altered in its chemical composition to become irre- 

 spirable. At very low pressures it becomes irrespirable even 

 though perfectly pure, for a reason which we shall give presently. 

 But the general fact which we have just mentioned is enough to 

 show that the carbonic acid given off in the confined space plays 

 no part in the death, since its proportion decreases progressively 



