^ CHEMISTRY. 431 



ten, on the strength of J)evill«- and Troost's research cvs, AI2 Cle, which 

 correspouiLs to a density of 1).20. According to Nilson and Pettersou 

 the density at 440° is 7.789, at 7r)8o it is 4.802, and above that temper, 

 atnre, from III70 to 12G(P, it is fairly constant at from 4.247 to 4.277. 

 The value 4.G00 corresponds to the molecule AlCl,, which is required 

 by the trivalency of aluminum, as indicated by the periodic law. 

 (Zeitsch. Physikal. Chem., T, 450.) 



On tlie other hand, Friedel and (3raits, at temperatures ranging from 

 2180 to 4o3^, find a vapor density of 9.24, agreeing with Deville and 

 Troost's determination. They get no evi«leiu;e of dissociation into any 

 simpler molecules. (Compt. Rend., cvi, 1704.) 



Conformable with these data Louise and lioux, working with alu- 

 minum methyl and aluminum ethyl, get values corresponding to the 

 general molecules AI2 Kfi. l^'or the same com[)ounds Buckton and Od- 

 ling long ago found densities according with Al !?> IJoth compounds, 

 according to Louise and lioux, decompose at high temperatures, yield- 

 ing aluminum, hydrogen, and hydrocarbons. (Compare also the data 

 obtained by the same authors by Raoult's method, as cited in the pre- 

 ceding article. (Compt. Rend., cvi, 7;> and 602.) * < 



Altogether the evidence seems to ])rove the existence of AliR,; mole- 

 cules, which split u]i at high temperatures into two of Al R;;. 



Ferric chloride, if re2Cl,i, requires a vapor density of 11.2. If FeCls, 

 its value should be 5.6. Griinewald and V. Meyer obtain the following 

 values: At 448°, 10.487 ; at 518°, 9.569 ; at GO60, 8.383; at about 750°, 

 5 389 to 5.528, with evidence of dissociation ; at about 1050°, 4.915 to 

 5.307, and similar figures at higher temperatures. At 448° it vaporizes 

 completely undecomposed, and even then its vapor density is too lowfor 

 Fe-iCl,;. That compound, therefore, they believe does not exist; and 

 regard the lower symbol, FeCl;., to be the true one. At the higher tem- 

 jieratures it splits up to some extent into FeCl.. and free chlorine. (Be- 

 richte, XXI, 687.) 



To this investigation, as to Nilson and Petterson's on aluminum chlo- 

 ride, Friedel and Crafts reply. They determine the vapor densit}^ of 

 ferric chloride in presence of free chlorine, in order to ]>revent any de- 

 composition, and lind a figure agreeing with Fe^Cl,;. Their data are 

 for temperatures from 321° to 342°. (Compt. Rend., ovii, 302. Com- 

 pare liiltz, P>erichte, xxi, 2760.) 



Ferrous chloride, redetermined by Nilson and Pettersou, at tem- 

 peratures varying from 1300o to 1500°, has a density of 4.292 to 3.340. 

 Theory for FeCI^, 4.375. Earlier work by V. Meyer seems to indicate a 

 more comi)lex molecule at lower temperatures. (Journ. Chem. Soc, 

 Liii, 827.) 



Nilson antl J*etterson also have determined the vapor density of 

 chromic and chromous chlorides. For the former, al 1200^ to 1300°, it 

 agrees closely witli the molecule Crl-l:. At 1065^ a iiighei- value was 

 found, but not at all aitproxiiuaflug to Cr/Jlfi. The latter probably v/4)k 



