90 On the Expansion of Water at High Temperatures. 



At first sight we are therefore led to conclude that the dis- 

 solved salt gradually expands up to about 75°, and then gra- 

 dually contracts, so that its bulk at 200° is only about |ths of 

 what it is at 75°. We cannot, however, suppose that this result 

 is in reality due to the contraction of the salt, but it appears far 

 more probable that it is to be explained in the following manner. 

 Before being mixed, the respective volumes of the chloride of 

 potassium and the water in I'OOOO part of the solution would be, 

 as shown above, '1466 and -8534. According to the experi- 

 ments of Playfair and Joule *, the expansion of chloride of potas- 

 sium from 0° to 100° is •01094, and therefore, providing that this 

 expansion be uniform, the volume of the '1466 part, at the tem- 

 peratures given in column I. of the following Table, would be as 

 shown in column II. According to my own experiments, the 

 volumes of the '8534 part of water would be as in column III. ; 

 and these, added to the corresponding numbers in II., would 

 be the total volumes given in IV., which the salt and the water 

 would occupy before being mixed together. When, however, 

 the salt is dissolved, the experiments described above prove that 

 the actual volumes are as given in V.; and subtracting these 

 from those in IV., we obtain the values shown in VI., which 

 represent the reduction in volume that takes place when the salt 

 is dissolved. Subtracting these values from the corresponding 

 numbers in II., and calculating the difference on the supposition 

 that in each case the numbers in II. are taken for unity, we ob- 

 tain column VII., representing the relative volume with which 

 the salt enters into solution, if no part of the diminished volume 

 be ascribed to a contraction of the water. The results for 300° 

 are deduced by means of the formulae already given ; but the rest 

 are all determined from the experiments. 



It therefore appears, from the facts shown by column VII., 

 that, according to the above supposition, the volume with which 

 the salt enters into solution is not the same at all temperatures. 

 Not taking into account the very lowest temperatures, as being 



* Chemical Society's Memoirs, vol. i. ]>. 121. 



