340 Dr. J.' H. Gladstone on Chromatic Phenomena. [Feb. 6, 



broader than these : the violet and green were more quickly ab- 

 sorbed than the blue rays, and these more quickly than the orange 

 and red. The speaker observed, that all 

 the solutions of chromium salts which he 

 had examined, whether green, blue, or red, 

 gave a prismatic image of the same form, 

 — that described above, — the only percepti- 

 ble difference being in the relative lumin- 

 osity of the different colours : thus, on ex- 

 amining the green and blue modifications 

 of nitrate of chromium in solutions of the 

 same strength, the green in the first case 

 appeared brighter than the blue, and pene- 

 trated to a somewhat greater distance, while 

 in the second case it was the blue that had 

 the advantage in luminosity ; but the general 

 configuration of the prismatic image was 

 identical in the two modifications so different in appearance to the 

 unaided eye. This was not the only instance in which the prism had 

 revealed a wider application to the general rule, that a particular base 

 or acid has the same, or very nearly the same effect, upon the rays of 

 light, with whatever it may be combined. When two colouring sub- 

 stances combine, each continues to exert its proper influence on the 

 various rays ; thus, acid chromate of copper is yellowish green, 

 because the chromic acid absorbs the blue and violet rays, and the 

 cdpper the red ray, and thus orange, yellow, and green are alone 

 transmitted. The diagrams also explained the production of first 

 green, and afterwards red, on the admixture of sulphindigotate and 



Lavender. 



Sulphindigotate of Potash. 



Chromate of Potash. 



chromate of potash. Sulphindigotic acid and its salts admit the 

 extreme red freely, but absorb the orange at once, the yellow very 

 speedily, the green not so soon, and admit the blue and violet to 

 a considerable distance : these last, however, are completely absorbed 

 by chromic acid and the chromates ; thus, a little red and much 



