190 ELECTROCHEMISTRY 



The presence of a labile atom in a molecule leads, not unusually, 

 to the development of color in solution, due to the absorption 

 of light-vibrations by the vibrating atom. The development or 

 non-development of absorption-bands in the visible or photo- 

 graphic spectrum will, of course, depend upon the* ratio of the 

 frequency of vibration of the labile atom to the frequency of the 

 light-waves which impinge upon it. That the presence of ab- 

 sorption-bands in the visible spectrum is not an inevitable con- 

 sequence of the presence within the molecule of a labile hydro- 

 gen atom is shown by the analogous instance of an equilibrium 

 between the keto- and enol-forms in the colorless hydantoins (5). 



(ii) The above-mentioned authors still consider that electro- 

 phoresis experiments show the presence of only one protein ion. 

 Now this is unquestionably the reverse of the fact. While it is 

 true that a superficial consideration of Hardy's results, alluded to 

 in the preceding section of this chapter, might encourage such a 

 supposition, we have seen that more careful analysis of the condi- 

 tions of the experiment shows that his results admit of a very 

 different interpretation, while the experiment cited at the end of 

 section 3 showing that in solutions of casein in which the minimal 

 valency of the casein ion, on the supposition that potassium casein- 

 ate yields only one protein ion, must be 4, the loss of protein in 

 the cathodal arm during electrolysis is only one-half the loss in 

 the anodal arm, is totally inconsistent with the view that protein, 

 during electrolysis, migrates in only one direction. 



Direct proof, however, of the simultaneous migration of protein 

 to both poles under the influence of an electric current is fortu- 

 nately available. Stirling and Brito (35) have shown that if a 

 direct current be allowed to traverse a solution of hsBmoglobin, 

 deposition of crystals of haemoglobin occurs at both electrodes. 

 An alternating current is without effect. Howell (11) has fur- 

 thermore shown that if a direct current be passed through a 

 solution of fibrinogen, the fibrinogen increases in concentration 

 at both poles although, as might be anticipated, the solutions of 

 fibrinogen obtained from the neighborhood of the two poles differ 

 in some particulars from one another in their behavior towards 

 thrombin. Since haemoglobin is a crystalline protein and fibrin- 

 ogen, as Howell has recently shown, is converted by thrombin 

 into a crystalline protein (fibrin), it cannot be urged that in these 

 cases we are dealing with the opposite migrations of two distinct 



