352 Mr. J. J. Waterston on Liquid Expansion. 



vdt 



— , corresponding to fi/3 and 8 8 straight lines, assumed to be 



the loci of -j- at the extreme upper part of the range. 



It will be remarked that P s = P m very nearly in these two 

 liquids; but this must be an accidental coincidence, as the nume- 

 rical value of P obviously varies inversely as the numerical value 

 which may be arbitrarily given to the volume at 0°. 



There are various considerations with respect to molecular 

 volume, aud the relation of h and 7 reckoned from the zero of 

 gaseous tension, that it would be proper to enter upon if it were 

 decided that this is the true general law of liquid-expansion ; 

 but, as in the former case, we may be too hasty in this. I only 

 hope that what is here set forth may lead to further inquiry. 

 The simplicity of the new differential equation is greater than 

 the previous one — a material point in its favour, since true pro- 

 gress and simplicity seem always to go together. 



Note. 



If the true theory of liquid-expansion has now been discovered, 

 other symmetrical relations are likely to appear, and more espe- 

 cially in those bodies of similar composition, as the hydrochloric, 

 hydrobromic, and hydriodic ethers, which have fortunately been 

 experimented upon both by M. Regnault and by M. Pierre. 



The following will serve to show how far their observations 

 strictly respond to certain relations presumed to exist between 

 the constants of the thermo-molecular lines of those bodies. 



The vapour-density lines of the three ethers, (1) CH 2 . H^ CI 2 , 



(2) CH 2 .H*Br* and (3) CH 2 . H* I*, projected from RegnaiuYs 

 vapour-tensions (dynamic series) below atmospheric pressure, 

 give the following values for g and h in the general equation 



fr'IH 



in which both t and g are reckoned from —274°, the zero of 

 gaseous tension. 



9 



(1) 117-0 143-7 1-2281 



(2) 125-9 161-0 1-277 L Mean 1-237. 



(3) 145-1 175-1 1-207 J 



General mean of 16 liquids is also 1*237. 

 It will be observed that the numbers in the two columns fol- 

 low the same ratio very nearly, showing that the lines all meet 



