STUDY OF THE PHYSICAL CHEMISTRY OF ANAESTHESIA 165 
or normal saline solution. This fact is of importance in regard to the mode of 
action, as it definitely points to an interaction between the chloroform and the 
proteid present. 
The presence of fats would, of course, increase the apparent solubility of 
chloroform in serum, and hence it is necessary in all cases to use perfectly clear 
serum, free from suspended fat ; this precaution we have always been careful to 
observe ; and, in addition, the serum has always been centrifugalized. 
In this connexion, it may be added that the haemoglobin solutions which we 
have employed could not contain any appreciable amount of fatty matter, and hence 
the high solubilities which we have observed could only arise from chemical interaction 
between the haemoglobin and the chloroform. 
Methods for Determining Maximum Solubility 
Three methods have been used in the determination of the maximum solubility 
of chloroform in the solvents mentioned above, which have given concordant results, 
and shown that the solubility in proteid solution is much higher than in water or 
saline. 
In the first method we have determined the amount of chloroform dissolved by 
obtaining the product of volume and vapour pressure at low pressure and with a 
small volume of fluid, so that practically all the chloroform was simply pumped off 
into the vacuum. In this method the volume of fluid experimented with is 
necessarily small, and this gives rise to experimental error of measurement, which is 
added to by the volume measured being large and pressure small, so that the results 
are only approximative, yet it is observable that they confirm those obtained by the 
more accurate methods described below. 
The details of the method are described in the succeeding section on the 
relationship between vapour pressure and concentration of chloroform, and it need 
only be mentioned here that we have obtained solubilities of 0-95 per cent, in 
normal saline (0*75 per cent.), 3-33 percent, in serum, and 4-42 per cent, in whipped 
blood by this method. 
The second method employed consists in weighing out known amounts of 
chloroform into water and serum and haemoglobin solution respectively, and then 
determining by direct observation that concentration in each case at which the chloro- 
form ceased to be dissolved. 
This method of observation is made easv in the case of chloroform by the high 
specific gravity of that fluid, as a result of which, on inverting the flask in which the 
determination is being made, even minute globules of undissolved chloroform can be 
seen falling through the fluid. 
The determinations of solubility by this method are made on the following plan : 
Pure chloroform is dropped from a fine capillary pipette into a tared graduated flask 
