Volumes, and Chemical Characters of Liquids. 413 



other observers, which I believe are of sufficient interest to 

 warrant me in discussing them now. It is not claimed that 

 the law which will be put forward is at all complete or final 

 in form ; but the evidence certainly shows that it is at least 

 a first approximation to an exact law. Before proceeding 

 further, I should state that I find that the relation in question 

 has already been to a certain extent noticed by J. A. 

 Groshans, who cited one or two instances of it in a paper 

 published four years ago and discussed these instances in the 

 light of his " Law of Density Numbers " ( Berichte, xix. p. 974). 

 So far as I am aware, it has not otherwise been noticed. 



To save circumlocution, I shall use the phrase compounds 

 of the same group to signify compounds of the same hydro- 

 carbon radical with elements of the same natural group. 

 Thus ethyl fluoride, chloride, bromide, and iodide form one 

 group ; the oxide, sulphide, selenide, and telluride form 

 another ; ethylene halides a third ; and chloroform and bromo- 

 form belong to a fourth. The law may then be stated as 

 follows:— The ratio of the molecular volume at the boiling- 

 point to the temperature of ebullition reckoned from absolute 

 zero is a constant quantity for all compounds of the same 

 group. More fully stated it amounts to this : — 



If liquid compounds of the same group be compared at 

 temperatures at which their vapour-pressures are equal, the 

 volumes occupied by unit weights are inversely proportional to 

 the molecular weights and directly proportional to the absolute 

 temperature ; or 



D xT s f =a constant (c) . . . . (1) 



for each group, vapour-pressure being equal. In this formula 

 M = molecular weight, D T = density of the liquid at T°, T = 

 absolute temperature of ebullition, and Vt= molecular volume 

 at T°. It will be shown that, so far as the law can be at 

 present tested, the deviations are small but real. 



This may be compared with the following, which is but a 

 special statement of two familiar laws of much wider applica- 

 tion : — If vapours of the same group [or any vapours] be 

 compared at different temperatures but equal pressure, the 

 volumes occupied by unit weights are inversely proportional 

 to the molecular weights and directly proportional to the 

 absolute temperatures : or 



d xT = ^ = a constant (c l ), . . . (2) 



Phil Mag. S. 5. Vol. 30. No. 186. Nov. 1890. 2 F 



