of Water from Salt-Solutions. 503 



to the nature of the action of salts on the vapour-pressure of 

 the water in which they are dissolved, I commenced in April 

 1884 a series of experiments on the subject, the first portion 

 of which, relating to the boiling-points of saturated solutions, 

 has been already published*; while the general conclusions 

 arrived at up to the middle of 1885 are to be found in a report 

 on Solution, presented to the British Association in that year. 

 Since then I have repeated my experiments with improved 

 apparatus, with the result that my previous conclusions are 

 extended and confirmed, so that I feel myself justified in 

 publishing this second part of the research. 



Before proceeding to an account of my own experiments, it 

 will be advisable briefly to summarize the results obtained by 

 Legrand (he. cit.). 



His experiments were conducted as follows : — 



After he had determined the boiling-point of pure water by 

 heating it in contact with some granulated zinc in a wide 

 test-tube, in the neck of which was fastened a delicate ther- 

 mometer the bulb of which was immersed in the water, he 

 introduced a known quantity of the salt under examination 

 and again observed the boiling-point. The tube was weighed, 

 and thus the quantity of water present was ascertained. A 

 further quantity of salt was added, and the operations repeated 

 until a saturated solution was obtained, the amount of salt in 

 which was determined in the ordinary way. From the results 

 thus obtained curves were drawn, and thus the quantities of 

 salt required to raise the boiling-point of water successive 

 half-degrees were found. 



On an examination of Legrand's figures, we find that the 

 seventeen salts examined in the above manner are divided into 

 four classes by their effect on the boiling-point of water. 



1. Several salts agree in this, that more salt is required to 

 raise the boiling-point the first half-degree than to raise it the 

 second, and this more than the third, and so on : thus, 7 '5 per 

 cent. NaCl raise the boiling-point to 101° C. ; 5*7 per cent, 

 raise it from 101° to 102° C; 4*9 per cent, raise it from 102° 

 to 103° C. ; &c. The salts which behave in this way are 

 NaCl, KC1, Na 2 C0 3 , Na 2 HP0 4 , and BaCl 2 . 



2. One salt only, KC10 3 , has its effect on the boiling-point of 

 water represented by a straight line : n (14*64 per cent.) KC10 3 

 raise it n° C. 



3. Other salts behave in a manner the converse of those in 

 class 1 ; i. e. as the concentration increases so does the amount 

 of salt required to raise the boiling-point each successive 

 degree. NH 4 N0 3 , NaN0 3 , and KN0 3 behave in this way. 



* Phil. Mag. October 1884. 

 2M 2 



