590 



SCIENCE. 



[N. S. Vol. XIV. No. 355. 



inferred that both solutions contain iden- 

 tical colloids, but that the Graham's colloid 

 contains also considerable inactive crystal- 

 loid hydrate. The absorption curve then 

 suggests that the crystalloid has an absorp- 

 tion curve lying between hydrolized ferric 

 chloride and non-hydrolized ferric chloride. 

 (To be printed in Physical Review.') 



9. ' Note on the Transmission of Radia- 

 tion by Thin Films of Asphalt': E. L. 

 Nichols, 



10. ' The Faraday Effect in Solutions .of 

 Hydrolyzed Ferric Chloride ' : Fred. J. 

 Bates, University of Nebraska. 



The rotation of the plane of polarization 

 in optical transparent substances, when the 

 light is transmitted along the lines of mag- 

 netic force, has been the subject of numer- 

 ous experiments since the days of Faraday, 

 and is known as the ' Faraday Effect.' 

 There have been many determinations of 

 the molecular rotation of substances in 

 solution, but little effort to determine 

 whether the effect in solution arises from a 

 molecule or from an ion or from both. Ob- 

 servations have also frequently been limited 

 to one color (and perhaps then a mixed 

 color), or to a few colors. It seemed de- 

 sirable to extend these observations to dif- 

 ferent parts of the spectrum. This is 

 particularly true of colored solutions, whose 

 colors correspond hypothetically to the free 

 periods of their vibrations, affecting the dis- 

 persion and probably the rotation of the 

 plane of polarization. 



Ferric chloride solutions afford a good 

 means of testing this phenomenon. Ob- 

 servers have noted that the molecular 

 rotation of this substance decreases upon 

 dilution of the solution. This suggests that 

 the rotation arises from the molecules 

 rather than from the ions. The writer 

 tried a solution of sufficient concentration 

 to give him a rather large rotation. The 

 solution was then diluted enough to leave 

 the effect slightly but certainly noticeable. 



If the rotation was proportional to the con- 

 centration, no effect was observed, which 

 suggests that the ions are inactive or pos- 

 sess very small rotary power in comparison 

 to that of the molecules. Observations by 

 Goodwin and Moore show that dilute solu- 

 tions of ferric chloride hydrolyze and finally 

 form a new product, colloid ferric hydrate. 

 It was thought that by restoring an iron 

 molecule by this process there would pos- 

 sibly be a small rotation where previous 

 ionization had made it unobservable. By 

 this test it was found that the required 

 dilution to obtain sufficient hydrolysis 

 made the quantity of iron too small to give 

 any further evidence by the usual method 

 of observation. However, the use of a sun- 

 light spectrum showed an effect as soon as 

 one began to pass from the transparent 

 spectral region into the absorption region. 

 The half-shade polariscope could be read 

 to 0.01°, and in the red the difference be- 

 tween a .01 normal solution (hydrolysis 

 forced by heating the solution) and water 

 was not more than 0.01°. The difference 

 between an unhydrolyzed solution of this 

 concentration and water was also unob- 

 servable. Upon examination of the hy- 

 drolyzed solution at a point in the green 

 where the absorption is very marked, a ro- 

 tation of .79° was observed, while at the 

 same point the other two solutions showed 

 no difference. That is, we have here an 

 anomalous rotary polarization or ' Faraday 

 Effect,' analogous to anomalous dispersion. 

 It is clear that in this case the anomaly 

 arises from molecules in the region of their 

 absorption. It remains to be seen whether 

 such an anomaly will also arise in solution 

 where the absorption arises from ions. 



11. ' Discharge of Electricity from Glow- 

 ing Platinum and the Velocity of the Ions ' : 



E. BUTHERFORD. 



A rectangular platinum plate 14 cm. 

 long, 7.5 cm. wide and .002 cm. thick, 

 was heated to incandescence by an electric 



