386 Dr. W. W. J. Nicol on the 



3. So markedly is this the case that at or below 100° C. 

 the difference between the volumes of water and of a salt- 

 solution of the same volume at 0° C. actually changes its sign 

 in many cases. 



4. It is therefore possible in the case of every salt-solution 

 to find a temperature at which its coefficient of expansion is 

 the same as that of water at that temperature. According to 

 de Heen* this temperature is dependent only on the nature 

 of the salt, and is the same whatever be the strength of the 

 solution. Kremersf, on the contrary, holds that this last has 

 some slight influence. 



5. No connexion can be traced between the expansion of 

 a salt in the solid state and that of its solution (Grerlach, loc. 

 cit.). 



In the course of experiments on the nature of solution it 

 appeared to me probable that there exists a connexion be- 

 tween the increase of solubility with rise of temperature and 

 the rate of expansion of solutions of the salts. With the 

 object of ascertaining whether or not such a connexion exists 

 I made a series of experiments on the subject ; for I found 

 that the results obtained by previous experimenters either 

 were not numerous enough or required confirmation. While 

 in all cases they were not suited for my purpose, owing to 

 the solutions experimented with being of percentage com- 

 position, and thus requiring recalculation into terms of mole- 

 cules of salt per 100 H 2 0. Even when this was done the 

 differences in the strengths of the various solutions were so 

 irregular that any conclusions derivable from the results were 

 extremely unsatisfactory. 



The present paper contains the results of experiments on 

 solutions of the four salts NaCl, KC1, NaN0 3 , and KJST0 3 , at 

 temperatures between 20° 0. and 80° 0. The solutions were 

 as nearly as possible molecular, and differed from one another 

 in the case of each salt by two molecules of salt ; for the 

 reasons given below, it will be seen that it is almost impossible 

 to use solutions of the precise composition aimed at. Still 

 the error thus introduced is practically eliminated by the 

 method of calculation employed. 



In the determination of the expansion of a liquid two 

 general methods are available, each presenting certain points 

 of advantage over the other. I finally decided to employ the 

 dilatometric in preference to the pycnometric method ; and I 

 Jiad the less hesitation in doing so, as I found it possible to 



* Physique Comparee. Bruxelles, 1883, p. 76. 

 t Pogg. Ann. cvi. p. 382 (1858). 



