AQUEOUS SOLUTIONS. M^KAY. 323 



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) 2 , 50 c.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 c.c. The 

 flasks were filled to the mark when the salt solution and water 

 added had been well mixed and had attained a temperature at 

 or near 18C. 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 c.c. 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 



