AQUEOUS SOLUTIONS. 
MCKAY. oon 
platinum tube which he used, however, for condensing the water 
vapor, a block-tin tube was used. Generally, too, only the 
second distillation described by him was carried out, ordinary 
distilled water of a conductivity of 1.87 being treated with 
Ba(OH),, 50 ¢.c. of a saturated solution to two litres. The water 
distilled in this last way had a conductivity of about 1.11. 
Methods of Making up Solutions. 
The general plan adopted in making up a series of solutions 
of any salt was to dilute strong solutions by means of pipettes 
and measuring-flasks. In measuring off volumes of strong solu- 
tions the pipettes were rarely of smaller volume than 50 cc. The 
flasks were filled to the mark when the salt solution and water 
added had been well mixed and had attained a temperature at 
ornear 18°C. The calibration of the flasks and pipettes will be 
described in a future paragraph. Analyses were made of two 
or three of the solutions thus formed, of intermediate concentra- 
tions, and from these the concentrations of the other solutions of 
any one series were determined. 
To obtain solutions with smaller differences of concentration 
than could be conveniently got by the above method, a known 
quantity of one of the solutions of a series, generally a volume 
of 100 c.c., was placed in the dry conductivity cell and diluted by 
small additions of water down to the next solution in the series. 
5 ce. were generally added four or five times from a pipette. 
After each addition of water had been made, and the liquid well 
mixed, a conductivity measurement was made. An analysis of 
the final solution was also made if the solution was not very 
dilute. In that case it was assumed that the increase in the 
volume of the solution was equal to the volume of water added. 
With the stronger solutions made up in this way, the shrinkage 
in the combined volumes of solution and water as shown by the 
experimentally determined concentration of the final solution 
was apportioned equally among the intermediate dilutions. 
Judging from the course of the curves representing conductivity 
and concentration good results were attainable is this way up to 
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