STUDY OF THE PHYSICAL CHEMISTRY OF ANAESTHESIA 
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The ratio of the vapour concentration in the fluid to the concentration in the 
vapour space gives the coefficient of distribution [coefficient de partage, Tkei/ungs- 
coefficient) ; this should remain constant if the absorption of the chloroform vapour 
by the liquid were normal and strictly proportional to the vapour pressure, and if it 
varies it points to a physical or chemical aggregation or compound between the 
chloroform and the fluid or its constituents (vide infra). 
Method of Reading. — The readings were taken with a cathetometer,' placed about 
four feet from the tubes, both for greater accuracy in reading than direct measure- 
ment would give and to avoid changes in temperature. 
Two Methods of Experimentation. — We have employed two different methods of 
experimentation in investigating the variation in vapour pressure with varying con- 
centration. It is obvious that the concentration of a measured volume of a strong 
solution introduced into the densimeter may be diminished by pumping off more 
and more chloroform, by increasing the volume of the vapour space above the 
solution. 
A series of readings of differences in pressure may thus be obtained in which 
the vapour space on the two sides is kept equal and of known and increasing value 
throughout the series. This method we have called the method of variable vapour 
space. 
On the other hand, a series of solutions of known and steadily diminishing or 
increasing concentration may be introduced into the densimeter and measured one 
after another as to their vapour pressure, in each case with a known fixed volume of 
vapour space. As stated above, the concentration at which each vapour pressure in 
the series is measured is then accurately known. This method we have called the 
method of constant vapour space. 
Method of Variable Vapour Space. — In this method, unless the volume of the 
tubes of the densimeter is very large, the volume of solution and solvent respectively 
introduced must be very small. We have usually taken J c.c. on each side, either 
of a saturated solution or of a very strong solution of known strength, and, by altering 
the levels of the tubes and mercury receiver, have taken a long series of readings, in 
each case with equal volume of vapour space on each side, at every increasing volume 
of vapour space, until the difference in pressure became of small value, and the 
product of volume and vapour pressure became approximately constant, showing that 
practically all the chloroform had been pumped off from the solution. This constant 
product then gave the necessary datum for calculating the concentration of the 
original solution introduced into the densimeter, the product of the vapour pressure 
and volume at each stage gave the datum for calculating the quantity of chloroform 
pumped off from the solution, and, therefore, for deducing the corresponding 
I. The instrument used was made by Pye and Co., of Cambridge, and, by means of a vernier and divided screw-head, 
read to ^ mm. We have frequently observed that we were able to take readings within five divisions, that is 2 \ mm., which 
is far within the accuracy of other portions of our determinations. 
