i 7 4 THOMPSON YATES AND JOHNSTON LABORATORIES REPORT 
concentration of solution. Or, also, by plotting vapour pressures as abscissae, and the 
product of vapour pressure and volume of vapour space as ordinates, the ratio of 
vapour pressure and amount of chloroform absorbed at each stage could be shown. 
The method of variable vapour space has, however, two working disadvantages 
which caused us in the end to abandon it and replace it by the method of constant 
vapour space. The first objection is that the amount of solution taken is small, hence 
it is difficult to measure it with accuracy, and to make ic equal on the two sides. 
The second objection is that at the low concentrations the increase of volume for 
a small fall in pressure is very large, and hence the determinations become inaccurate, 
a small error in pressure-reading; making a large deviation. The values for high 
pressures are also inaccurate., but for a different reason ; these readings are taken with 
small volumes of vapour space, and unless the vapour spaces are accurately equal on 
the two sides, there is a large disturbance due to inequality in pressure of the previously 
dissolved gases pumped off on the two sides. 
The results, however, in the intermediate pressures are accurate and are given 
below, as they confirm those given by the other method. 
Method of Constant Vapour Space. — In using this method we have always introduced 
a volume of 5 c.c. of the solvent on one side, and 5 c.c. of a solution of known 
strength on the other, and have invariably adjusted the levels so that at the temperatures 
of observation there was a vapour space of exactly 5 c.c. on each side. 
In some cases we have started with a saturated solution of chloroform, and have 
then made dilutions of different percentages of that solution in the manner described 
below. In the later experiments we found it, however, more expedient, on account 
of knowing the exact concentration directly, to prepare a solution of known strength, 
say one per cent., and for the more dilute solutions to use various percentage dilutions 
of this stock solution. The more concentrated solutions were obtained by making up 
solutions varying by one per cent, in strength, and one-half per cent, differences were 
got by mixing these with each other in equal proportions. For percentages less than 
O'l per cent., a cri per cent, solution was first prepared by making a ten-fold dilution 
of the one per cent, solution, and this o*i per cent, solution was then diluted similarly 
to the one per cent, solution. 
Precautions in Preparing, Preserving, in Unaltered Strength, and 
Diluting by Known Amounts, of the Solutions Used 
In working with the solutions it is indispensable that due precautions be taken 
against loss by escape of chloroform into the air during the various manipulations. 
If a portion, for example, of a stock solution of known strength be pipetted off 
for use in the densimeter, and then the stock bottle be merely stoppered, the air 
space over the portion of solution left in the bottle rapidly becomes charged with 
chloroform vapour at the expense of the stock solution, and a second sample taken 
