116 DIRECT PROPERTIES OF MOLECULES 319 



116. Values of the Molecular Diameter 



The calculation of the molecular diameter s- may be 

 actually carried out for a large number of gases and 

 vapours, since now not only their mean free paths are 

 known from measurements of viscosity and diffusion, but 

 also their densities in the liquid state. 



I first of all tabulate the necessary data as to density in 

 the liquid state of the series of gases whose free paths are 

 sufficiently well determined from viscosity experiments ; 

 and wlien several determinations are to hand for the same 

 material I shall always choose the greatest, as this is to be 

 preferred for our purpose. 



For the density of liquid sulphurous acid Is. Pierre 1 

 found the value 1'49 at 20 ; for liquid ammonia 

 A. Lange 2 obtained the value 0-6954 at 50; for liquid 

 carbonic acid Cailletet and Mathias 3 found 1-057 at 

 34, and the same observers 4 determined the value 1-003 

 for nitrous oxide at 20*6. The density of liquid ethyl 

 chloride is given as 0-9216 at by Is. Pierre, 5 0-9176 at 

 8 by Linnemann, 6 0-9253 at by Darling 7 ; of these 

 values I use the greatest 0*925. For methyl chloride Vincent 

 and Delachanal 8 found the density 0*9831 at 20. 



Faraday 9 has found 0*866 for the density of cyanogen 

 in the liquid state, and 0*9 for the approximate density of 

 condensed sulphuretted hydrogen. 10 An s del I 11 found for 

 hydrochloric acid 0'908 at 0. 



The density of liquid chlorine at 80 is given as 

 1-6602 by Knietsch, 12 and Cailletet and Mathias 13 found 

 that of liquid ethylene at 21 tobeO'414. Wroblewski 14 

 measured the density of liquefied oxygen at 200, and 



1 Ann. Chim. Phys. 1847 [3] xxi. p. 336. 



2 Zeitschr. f. Kalte-Ind. 1898, v. p. 39 ; Wied. Beibl. xxii. p. 265. 



3 Journ. de Phys. 1886 [2] v. p. 555. 4 Ibid. 1886 [2] v. p. 555. 



5 Ann. Chim. 1845 [3] xv. p. 362. 6 Ann. Chem. 1871, clx. p. 214. 



' Ibid. 1869, ol. p. 221. 



8 Comptes Rendus, 1878, Ixxxvii. p. 987 ; Ann. Chim. 1879 [5] xvi. p. 427. 



9 Phil. Trans. 1845, p. 169 ; Pogg. Ann. 1848, Erg. Bd. ii. p. 215. 



10 Phil. Trans. 1823, p. 193. 



11 Chem. News, 1880, xli. p. 75; Wied. Beibl. 1880, iv. p. 310. 



12 Ann. Chem. 1890, cclix. p. 100. 13 Journ. de Phys. 1886 [2] v. p. 555. 

 14 Comptes Rendus, 1886, cii. p. 1010. 



