1904.] Properties of Solutions of Chloroform in Water, etc. 397 



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 indispensible, 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 deter- 

 mination, but can be used throughout an entire experiment. 



By vigorous stirring, equilibrium can be attained in 5 — 10 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 



