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PHYSICS. — -Circular dichroism and rotary dispersion of certain salt 

 solutions. L. B. Olmstead. Physical Review, 35 : 31-46. 1912. 

 The author investigated the rotation and ellipticity produced in plane 

 polarised light by transmission thru solutions containing an optically 

 active acid radical combined with an absorbing metallic ion; and, in 

 connection with this, the extinction coefficients and refractive indices of 

 the same solutions. Readings were made at intervals of 10/x/x to 30/jlh 

 thruout the visible spectrum and the values obtained were plotted against 

 wave-lengths. The colored compounds successfully used to give circu- 

 lar dichroism were chromium, copper, cobalt, and manganese; and the 

 organic compounds were tartrates, malates, and lactates. The ellipticity 

 is of the order of 10~ 3 to 10 -2 for the concentrations used and is always 

 a maximum in the region of maximum absorption. The rotation is 

 anomalous in every case but the refractive index shows no anomaly. In 

 the chromium compounds the absorption curves are of the same general 

 shape with an absorption band in the yellow and one in the violet. At 

 about 570/xm the slope of the rotation curve is steepest and usually changes 

 sign; and at this point the ellipticity reaches a maximum positive or 

 negative value. In the copper compounds the ellipticity and absorp- 

 tion are maximum in the red, decreasing rapidly toward the blue. The 

 cobalt compounds reach their maximum ellipticity and absorption in the 

 green. The manganese tartrate solution shows an absorption band in 

 the violet and a slight one in the green. The ellipticity changes rapidly 

 from a negative value at 420/x/x to a maximum positive value at 540^, 

 decreasing again to a small negative value in the red. L. B. O. 



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