316 BESEAIiCIlES ON EVAPOTiATTON AND mSSOOTATTON. 



the heats of vaporization. (5) A relation exists between 

 the ratios of the absohito tomporaturos of all bodies, 

 whether solid or liquid, which may be expressed in the case 

 of any two bodies by the equation ]i' = E + dt' - i), whcro 

 B is the ratio of the absolute temperatures of the two 

 bodies corresponding to any vapoiir-prossure, the same for 

 both ; li', the ratio at any other pressure, again the same for 

 both; c is a constant, which may be or a small plus or 

 minus number, and t' and t the temperatures of one of the 

 bodies, corresponding to the two vapour-pressures. It may bo 

 noticed that the equation B' = Ji + c{t' - t) in not symmetrical, 

 in as much as t' and t may refer to either of the substances 

 compared; but the difference, within 5,000 jams, is small, 

 and may be neglected. When c=0, B'=B,, or the ratio of 

 the absolute temy)oratures is a constant at all pressures ; 

 and this is the case with chloro- and bromo-benzene, ethyl 

 chloride and bromide, and with the 28 others investigated 

 by Schumann. If the vapour-prossurcs of a substance in 

 the liquid and the solid states be compared with those of 

 a third substance, the sign of fi (+ or — ) for the solid is 

 always contrary to that for the liquid. This has been 

 proved for acetic acid and for bromine and iodine {Trans. 

 Ohem. Soc, 188fi, p. 453). (6) For higher pressures than 

 6,000 mms., the more complex equation, B,' = B + c(t' ~ I) 

 ^.g'(;'_i)2 gives more accurate residts. (7) The equation 

 B' — B + c{t' — t) holds where B' and B represent the ratios 



of the products''^' T (instead of the ratios of the absolute 

 dT 



temperatures) for any two substances at the same pressures. 



Space will not permit of a proof of these relations ; for 

 details we must refer to the original j)ap6rs. 



7. Vapour pressures of w.ercury. {Tram. Chim.. Soc, 188fi, 

 p. 37).— The vapour pressures of mercury were previously 



