202 M.C. Lea—Influence of Color upon Reduction by Lnght. 
The papers prepared with ferric salt alone, and also those 
with ferric salt in contact with the colors named, were simul- 
taneously exposed. They were then plunged into solution of 
ferridcyanide of potassium, which renders evident whatever 
reduction has taken place by the production of Turnbull’s blue, 
the unreduced portions remaining white. 
Result.—The series of experiments was carefully repeated 
three times. The aniline blue was found to be entirely with- 
out influence; the printed spectrum obtained corresponded in 
every respect with that of the plain ferric salt. The aniline 
green slightly diminished the impressibility, but not more in 
one part than another. Aurine produced this effect still more 
strongly. 
m, perhaps doubling it. But this increase extended, as it 
was judged, equally to all the rays. 
Potassium Bichromate. 
that substance in darkening and setting the aniline colors was 
found very objectionable, and little could be learned from the 
bands so obtained. Ferric ammonia oxalate was then substi- 
tuted with excellent results. : 
of the six colors above mentioned acted by diminishing 
the impressibility of the ferrid-cyanide, so that the printed 
spectra obtained were all weaker than that of the plain ferrid- 
eyanide paper used for comparison. But the weakening was 
general throughout the range of the spectrum, and no relation 
could be traced as existing between the color used and the 
impression made by particular rays, 
