358 PHYSICAL PROPERTIES 



From these results it is clear that the nature of the solvent plays 

 a very considerable part in determining the rotatory power of pro- 

 teins. Furthermore, it would appear that as a rule the salts which 

 proteins form with acids and bases differ very markedly in rotatory 

 power from the free protein (3) (20) (60) (1) (4) (6) (39). In an 

 analogous manner the rotatory powers of the salts which the simple 

 amino-acids form with acids and bases differ very markedly from 

 those of the free acids (40). As a rule too little attention has 

 been paid to this fact by investigators who have sought to char- 

 acterize the proteins by their rotatory powers. It is evident that 

 the specific rotatory power of a protein cannot be regarded as 

 characteristic of it until the nature of the protein salt and of the 

 solvent employed are rigidly defined. 



According to Alexander (1) the rotatory power of a dissolved 

 protein is considerably affected by exposure of the solution to a 

 high temperature for a period preceding the measurement. It 

 must not be forgotten, however, that partial hydrolysis of the 

 protein may play a very considerable part in bringing about this 

 change. 



2. The Absorption of Light by Protein Solutions. The 

 peculiar absorption-spectra of solutions of haemoglobin and its 

 colored derivatives have been very extensively studied (17) (19) 

 (63) (21) (22) (36) (5) (58) (14). From the results of these in- 

 vestigations it is evident that the absorption-bands (a and 0) in 

 the visible spectrum which are caused by these solutions are 

 primarily attributable to the haematin- and not to the distinctively 

 protein moiety of the haemoglobin molecule. In addition to 

 these bands, however, the absorption-spectrum of haemoglobin 

 and its derivatives reveals another absorption-band on the extreme 

 edge of the violet end of the visible spectrum (61) (2) (8). Ac- 

 cording to Gamgee (8) this absorption-band is given not only by 

 solutions of haemoglobin but also by solutions of haematin; he 

 therefore attributes it to the haematin, and not to the protein 

 moiety of the haemoglobin molecule. According to Soret, how- 

 ever, an absorption-band on the extreme edge of the ultra-violet 

 can be demonstrated, by employing a fluorescent screen, in the 

 absorption-spectra of solutions of a large variety of proteins, 

 among which may be mentioned egg-albumin, mucin (from 

 snails), casein, globulin and syntonin. This band is followed, on 

 the ultra-violet side, by a region of especial transparency. Accord- 



