172 THOMPSON YATES AND JOHNSTON LABORATORIES REPORT 
2. Before taking a reading, there must be certainty that each fluid is in 
equilibrium with its vapour space. This is shown by absence of variation when the 
apparatus is left at rest. 
For rapid and accurate working the mechanical stirring by means of the studs and 
magnet is indispensable, for even after the lapse of an hour when at rest the solution 
has not completely discharged its proper amount of chloroform into the vapour space. 
When once the control, containing, of course, no chloroform, has been thoroughly 
stirred it remains constant, and need not be changed at the end of each determination, 
but can be used throughout an entire experiment. 
By vigorous stirring, equilibrium can be attained in five to ten minutes, and the 
level does not afterwards change, no matter how long stirring, and observation be kept 
up. This important experimental observation we have taken occasion to verify 
several times during our experiments. 
3. For very accurate working, especially with the dilute solutions and low 
pressures, it is necessary in the case of serum and haemoglobin to pump off the 
dissolved gases by means of a Topler pump, otherwise these come off unequally from 
solvent and solution and disturb the results at the low pressures. The chloroform 
solutions are then made up from the pumped-out solvent, which also must be used for 
control and for making the dilutions. 
4. The temperature must be the same in the jackets surrounding each tube at 
the time when each reading is taken, and in a series of determinations at varying 
strength and a constant temperature, that temperature must be closely maintained 
throughout. The temperature error is a maximum when the solutions are near 
saturation, for then the variation in vapour pressure per degree is very large ; 
fortunately here the differences in level under observation are also very large, which 
diminishes the percentage error arising from small deviations in temperature. 
At concentrations away from saturation, the variations arising from small 
differences in temperature approximately obey the gas law, and under the conditions 
of our experiments become quite negligible. 
5. A correction must be made in all cases upon the concentration of the solution 
introduced into the tube for the amount of chloroform pumped off from the solution 
into the vapour space. This correction is, of course, larger in the case of the more 
concentrated solutions with high vapour pressures. 
This has been done in the experiments of which records are given below, and 
accounts for the concentrations not being exact percentages or small fractions of exact 
percentages. 
The amount of chloroform in the vapour space is readily calculated from the 
product of the observed vapour pressure and the volume of the vapour space, and this 
amount deducted from the quantity contained in the chloroform solution when it was 
introduced, gives the necessary datum for calculating the concentration in chloroform 
of the solution corresponding to the observed vapour pressure in the vapour space. 
