CHEMISTRY 125 



and /3-hydroxy-acids may also exhibit the phenomenon (Fischer and Scheibler, Ann., 

 IQII, 383, 337; McKenzie and Barrow, /. Chem. Soc., 1911, 99, 1910). It is noteworthy 

 also that a Walden inversion is accompanied by racemisation to a greater or less extent. 



In connection with the interpretation of the Walden inversion Emil Fischer has 

 adopted the view that the C-atom exerts an attractive force on atoms or groups outside 

 the molecule of which it forms part (Ann., IQII, 381, 123). That is, he assumes the 

 existence of auxiliary valencies (see E. B. xxvii, 847 et seq., article " Valency ") and sup- 

 poses that the formation of additive compounds precedes substitution. The position 

 taken up by the replacing atom or group is not necessarily that of the atom or group 

 which is replaced, so that in compounds containing an asymmetric C-atom substitution 

 may be accompanied by a change of configuration. From this point of view the Walden 

 inversion is a normal process which is as likely to occur as its opposite. Whether it 

 occurs or not depends on the character of the reagent employed and on the nature of the 

 groups attached to the asymmetric C-atom. Should the change of configuration not 

 occur in all the molecules involved then partial racemisation is observed. Werner pro- 

 poses a somewhat similar interpretation of the \Valden inversion (Ber., IQII, 44, 873. 

 Compare Pfeiffer, Ann., IQII, 383, 123). 



As regards new cases of optical isornerism, chief interest attaches to the preparation 

 of active compounds of phosphorus (Kipping and Challenger, /. Chem. Soc., IQII, 99, 

 626; Meisenheimer and Lichtenstadt, Ber., IQII, 44, 356), cobalt (Werner, Ber., IQII, 

 44, 1887, 2445, 3272), chromium (Werner, ibid., 3231), iron (Werner, ibid., 1912, 45, 

 433), and rhodium (Werner, ibid., 1228), and to the occurrence of optical activity in 

 l-methyl-cyc/ohexylidene-4-acetic acid and its derivatives (Perkin, Pope and Wallach, 

 /. Chem. Soc., 1909, 95, 1789; Perkin and Pope, ibid., IQII, 99, 1510). It is claimed 

 that the optical activity of this compound is due to the asymmetry of the molecule, not 

 to the presence of any particular asymmetric C-atom (for discussion of this point see 

 also Everest, Chem. News, IQOQ, 100, 29$; Proc. Chem. Soc., IQII, 27, 285; Marsh, ibid., 



Many workers are seeking to determine more definitely the quantitative connection 

 between rotatory power and the various correlated factors, such as temperature, solvent, 

 concentration, wave-length of the light employed, and the character of the atoms or 

 groups attached to the asymmetric C-atom (see, for instance, Walker, /. Physical Chem., 

 1909, jj, 574; Patterson and Stevenson, /. Chem. Soc., 1910, 97; 2110,. 1912, 101, 241; 

 Frankland, ibid., 1912, 101, 654). 



A physical method increasingly employed by organic chemists is the determination 

 of refractive power. Refractometric investigations have yielded especially interesting 

 results with unsaturated compounds, and recent work has confirmed and extended 

 Briihl's conclusion that the grouping C:C.C:C or C:C.C:O in any molecule is associated 

 with abnormally high refractive and dispersive power (see Briihl, /. Chem. Soc., 1907, 

 91, ii5;.Smedley, ibid., 1910, 97, 1475; Anwers and Eisenlohr, /. prakt. Chem., IQII, 84, 

 i, 37; Refraktometrisches Hilfsbueh,-'by Roth and Eisenlohr, IQII. Compare Thiele, 

 Ann., 1899, 306, 87). It is known that the mutual influence of contiguous unsaturated 

 atoms finds expression also in anomalous rotatory power (Hilditch, /. Chem. Soc., 1909, 

 95, 33i; ibid., IQII, 99, 224). 



Another point worthy of notice is the publication of several papers demonstrating 

 the applicability of the Barlow-Pope theory of valency volumes (see E. B. xxvii, 847; 

 Le Bas, /. Chem. Soc., 1907, 91, 112; Phil. Mag., 1907, 14, 324; 1908, 16, 60; Jaeger, 

 /. Chem. Soc., 1908, 93, 517; Jerusalem, ibid., 1909, 95, 1275; 1910, 97, 2190; 1912, 101, 

 1268; Colgate and Rodd, ibid., IQIO, 97, 1585; Barlow and Pope, ibid., 1910, 97, 2308). 



Physical Chemistry. In working out relationships between physical properties on 

 the one hand and chemical composition and constitution on the other, much success has 

 been achieved in the case of the refractive power of liquid substances. In this con- 

 nection the recent thorough revision of the atomic refraction and dispersion values is 

 noteworthy (Eisenlohr, Zeitsch. physikal. Chem., 1910, 75, 585). The new figures 

 (which take the place of those recorded in E. B. vi., 70), are as follows: 



