EXPEIUMENTAL KNOWLEDGE OF THE PROPERTIES OF MATTER. 469 



Acting on the principle wbich Crafts and Meier had used for iodine- 

 vapour, Friedel and Crafts ' obtained for alaminium chloride, by acting 

 under diminished pressure, a range of comparatively low temperatures 

 (218° to 433°), during which this body had a coefiScient of dilatation 

 nearly the same as that of aii- — not deviating more than CO2 does. By 

 the modification of Dumas' process they found vapour-densities through • 

 out this range of 215 degrees varying between 8'31 and 9'93, the higher 

 and lower values being indiscriminately scattered through this tempera- 

 ture-range. Now the value which Deville and Troost ^ had found was 

 9'35, corresponding to Al2Cl(; ; and Friedel and Crafts found this to be 

 practically constant from 218° to 433°. Within this range, therefore, 

 they assume that AloCIg is not dissociated into molecules AICI3. 



No fewer than twenty-one determinations were made for determina- 

 tions of vapour-densities within these limits of temperatui-e. 



Thus, though Nilson and Pettersson have proved that AICI3 is the 

 molecule at very high temperatures, it is proved that aluminium chloride 

 at lower temperatures can exist in the gaseous state as made up of ALClg 

 molecules. 



The same authors (Friedel and Crafts^) find that ferric chloride in an 

 atmosphere of chlorine was not dissociated at 440°, no deposit of crystal- 

 lised ferrous chloride being visible even at that temperature. Having 

 determined the densities of chlorine gas at different temperatures, and its 

 coefficient of dilatation, they used this as the gas with which vapour of 

 ferric chloi'ide was made to mix in the modification of Dumas' method. 

 The results deduced by them for the vapour-density of ferric chloride 

 between 321°'6 and 442°-2 were as follows:— 



temperatures 321°-6 ; 32o°-2 ; 356°-9 ; 357° ; 442°-2 ; 442°-2 

 densities. .11-41; 12-47; 12-04; 11-85 ; li-6G ; 11-30 



The number for FegCle is 11-25. 



Again, the same authors "* find for gallium chloride (B.P. 215°) in the 

 same way 11-73 at 237° ; Lecoq de Boisbaudran had found 13-4 at 247°, 

 and 11-9 at 273° ; the theoretical density for GaaClg is 12-2, which holds 

 approximately from about 237° to 273° ; the boiling-point is about 215° : 

 hence between these temperatures gallium chloride is Ga^Clg, which at 

 higher temperatures dissociates into GaCls molecules. 



Friedel and Crafts remark that AloClg, GagClg, In2Cl,, are more readily 

 dissociated into the smaller molecules the higher the atomic weight of 

 this group of metals. 



Vapour-densities of SulpJiur — Biltz. 



Finding that the tendency of investigations on vapour-densities is 

 apparently to give simpler molecules to some compounds, such as alu- 

 minium chloride, to which Deville and Troost had given the formula 

 AI2CI6, and to replace the formula Sn2Cl4 by SnCl2, FcjClg by FeCls, 

 Biltz undertakes ' to examine sulphur with the view of deciding whether 

 its vapour-densities give at any temperature-range the formula S^, and 

 whether they confirm the formula S2 at higher temperatures. For this 

 purpose he uses the form of apparatus which had been used by Griine- 



' C. R. 106, 1888, p. 1761. = Ann. Chim. Ph. 3, 58, 1860, p257. 



s C. R. 107, 1888, p. 301. ■• Loo. cit. 



5 Bcr. 21, 1888, p. 2013. 



