of Water and other Liquids. 409 



scarcely be accidental. The cases in which the individual 

 results fail to show any one of the above changes are chiefly 

 those where the results are deficient in number or accuracy. 

 The most marked exceptions to this statement being the 

 absence of indications of any change at 50°-60°, by Despretz's 

 or Matthiessen ; s results, and the absence of indications of 

 change at 10° by Rosettes results. 



It is true that there is some discrepancy as to the nature of 

 the first differential lines in some cases according to the dif- 

 ferent observers ; but a very small difference, or a constant 

 source of error, such as might occur in taking the temperature, 

 would account for this : the important point is the position of 

 the changes. 



The existence of more or less sudden alterations in the rate 

 at which density varies with temperature must, I think, from 

 reasons other than experimental ones be regarded as not 

 improbable. It can scarcely be doubted that liquids are 

 composed of various partially dissociated aggregates of their 

 fundamental molecules, and the instability of such complicated 

 bodies would, no doubt, be so great that a rise of a few degrees 

 would be sufficient to exterminate some particular one of 

 theni; and such extermination would result in the alteration in 

 the rate at which temperature would affect the densitv. The 

 existence of such changes, moreover, is in harruonv with that 

 of similar changes in the curves representing the effect of 

 temperature on the heat of dissolution of weak salt-solutions 

 (Trans. Chem. Soc. 1887, p. 290j. 



Further confirmation of the change at 50°-60° has been 

 found in some recent work of Tschernay (J. Russ. Chem. Soc. 

 1880, pp. 430 and 486). This physicist has examined the 

 expansion of solutions of six different nitrates and nine chlo- 

 rides, and finds that in all cases a change occurs at about 50°, 

 necessitating the use of different equations to represent the 

 determinations above and below that temperature*. I had at 

 first attributed this change to some peculiarity in the expan- 

 sion of glass, since it is well known that at about 50° o-lass 

 begins to experience some change which prevents it revertino- 

 at once to its original volume on cooling ; but I now think 

 that this explanation cannot be held, for most of the other 

 liquids which I have examined do not exhibit any change at 

 this temperature, and those which do so exhibit a change of a 

 very different magnitude from that exhibited by water. It may 

 also be pointed out that definite changes in the rate of expan- 



* I have not examined Tschernav's data to see whether they o-ive 

 evidence of anv changes besides that at 50°. 



