2^6 SCIENCE PROGRESS. 



-3 



a co-operative effect in increasing the refraction. Nasini 

 and Alderlini ($y) have measured the refraction constants of 

 non-metallic substances containing several groups, but find 

 the values are normal. It is thus indicated that the hioh 

 values of metallic carbonyl compounds are due to the metal. 



Nasini and Carrara (38) consider that furfuran and pyra- 

 zole, etc., have a centric structure. Refraction constants 

 have also been determined for furfurylic alcohol, pyromucic 

 acids and its salts (39), and for some organic phosphorus 

 compounds (40), but have led to no general results. 



Rotation of the plane of polarisation. — Most of the 

 work on optical activity may be grouped around Guye's 

 theory. Miss I. Welt (41) has measured the rotatory 

 powers of hydrocarbons containing the active amyl radicle. 

 Ethyl-propyl and isobutyl-amyl have almost the same 

 rotatory powers, the values being about half that of diamyl. 

 The facts accord with the views of Guye and Gauthier. 

 The rotatory power slightly diminishes as the temperature 

 rises. In the case of the ethereal glycerates and diacetyl 

 glycerates, on the other hand, as in the case of the tartrates, 

 Frankland and McGregor (42) find that the rotatory power 

 increases with the temperature. In general their results 

 do not accord with Guye's theory. They find that in the 

 series of diacetyl glycerates the homologue with the 

 maximum rotatory power is lower in the series than the salt 

 w T ith the heptylic radicle ; according to theory the salt with 

 the C„ radicle should have the maximum value. Since 

 methyl and ethyl diacetyl glycerates contain groups of 

 equal mass attached to the asymmetric carbon atom, they 

 ought to be inactive ; both are, however, powerfully active. 

 Again, the alteration in the rotatory power produced by 

 substituting acetyl, propionyl, and benzoyl, for the hydroxylic 

 hydrogen of methyl glycerate, is not in accord with theory. 

 Walden (43), who has dealt with twenty-six derivatives of 

 active amyl alcohol, and Piutti (44), who has worked with 

 derivatives of asparagine, come to the same conclusion as 

 Frankland and McGregor, namely, that the nature as well 

 as the mass of the radicles attached to the asymmetric 

 carbon atom profoundly influences the rotatory power. 



