M. C. Lea — Sensitiveness of Silver Bromide. 463 



the deep red color of the solution passes to a clear yellow. 



with its full brilliancy. But the solution, if too large i 

 tion of coralline to the acid has not been added, is found to have 

 wholly lost its power of exalting sensitiveness to the green rays, 

 although the amount of color applied be made the same in both 



Absorption Spectrum of Coralline. — With a moderately strong 

 solution and a narrow slit, the transmitted band is confined to 

 the red rays. As dilution increases, the band widens, passes 

 the D lines, and transmits all the yellow rays. In all cases the 

 band is continuous, and shows neither intervals nor a second 



Coralline, then, forms no exceptio 

 above deduced from the examination 

 strong red coloration. 



Action of Colorless, or nearly Colorless., Substances c 

 ness to G-reen Rays. 

 The following substances examined, gave an ir 

 sitiveness : 



Potassic arsenite. Morphia acet 



iVrgentic arsenite. 



Salicine. 



Codeia. 





Tinclure . 

 Ammoniu 

 Caffeine ? 



of capsicum, 

 m valerate. 





irs, therefore, that it 



is 



not among 



• the colored. 



but 



It appears, tnererore, tnat it is noi among ine coiorea, out 

 the colorless substances, that we must look for those capable of 

 enhancing sensitiveness to green light While not a single red 

 substance could be found that possessed that property, no less 

 than eight colorless substances exhibited it. 



The following substances neither increased nor diminishcl 



Ammonium hippurate. Pbloridzin. 



" mucate. Parabanic acid. 



" malate. Tincture of aloes. 



Plumbic arsenite. Potassic formate. 



It was a little uncertain whether two of these substances, 

 phloridzin and potassic formate, did not give a slight increase 

 of sensitiveness. 



The following colorless substances distinctly diminished the 

 sensitiveness to green light : 



Brucia. Gentianine. 



Strychnia. Podophylline. 



Narcotine. Aconitine. 



Daturine(tinct. of stramonium.) Asparagine. 

 Acid ammonium urate. Berberine. 



