M. C. Lea—Influence of Color upon Reduction by Light. 208 
Rosaniline and aniline green weakened the sensitiveness very 
slightly, almost imperceptibly ; mauveine and coralline much 
more, aurine and blue most of a 
he reduction undergone by potassium ferrideyanide may 
also be rendered evident by exposing the paper to the action 
of uranic nitrate, which strikes a deep red-brown with the 
ferrocyanide and a yellowish color with the unchanged ferrid- 
cyani complete series of papers examined in this way 
showed that all the colors tried, rosaniline, mauveine, aniline 
green, aniline blue, coralline and aurine, diminished the facility of 
reduction at the less refrangible half of the spectrum, and 
most of all the blue and coralline. As respect the more 
tefrangible half of the spectrum, all the colors acted injuri- 
ously, and each to about the same extent. 
Tange of rays from red to violet. The green diminished the 
sensitiveness to the less refrangible end rather more than to the 
more refrangible end, and the rosaniline and mauveine pro- 
uced scarcely any observable effect whatever. 
separate series of trials was made to test the effect of the 
colors on the impression of violet light as compared with white 
light, by giving much shorter exposures than in the preceding 
experiments. If coloring matters as such have any influence 
on the susceptibility to the action of particular rays, then a 
Tange of six colors extending from violet blue to deep red 
ought in some cases to favor the action of the violet, in others 
to interfere with it. But after very careful and repeated trials, 
it was found that all the colors lowered the sensitiveness to 
both violet and white, to both equally, and with all the colors 
to about the same extent. 
Uraniec Nitrate. . 
_The same range of coloring matters were tried with uranic 
nitrate, the extent of reduction being made evident by the 
subsequent application of potassium ferrideyanide, which with 
uranous nitrate gives a burnt sienna colored precipitate. 
