M. C. Lea—Chloride, Bromide and Lodide of Silver. 368 
compounds must wait for the next succeeding number of this 
Journal; here it can only be mentioned that these substances 
are formed much in the same way as the chlorine compound. 
They are less stable than it, and consequently the number of 
reactions that lead to their production is somewhat more lim- 
ited. Each, however, is formed in a great variety of ways, and 
with the same ease as the chloride. In color they are for the 
most part indistinguishable from it, but exhibit different reac- 
tions. 
RELATIONS OF PHOTOCHLORIDE TO HELIOCHROMY. 
The photochloride was examined both with the spectrum 
and under colored glass. 
The rose-colored form of photochloride was that which gave 
the best effect. In the violet of the spectrum it assumed a pure 
violet color, in the blue it acquired a slate blue, in green and 
yellow a bleaching influence was shown, in the red it remained 
unchanged. The maximum effect was about the line F, with 
another maximum at the end of the visible violet, less marked 
than the one at F. 
Under colored glass the colors obtained were brighter; under 
two thicknesses of dark ruby glass, the red became brighter 
and richer. Under blue glass some specimens gave a fair blue, 
others merely gray. Under cobalt a deep blue was easily ob- 
tained, and under manganese violet, a fine violet, very distinct in 
shade from the cobalt. Green produced but little effect— 
yellow was sometimes faintly reproduced but rarely. But the 
yellow glass of commerce, even the dark yellow, lets through 
portions of nearly the whole spectrum, as can readily be seen 
by testing it with the spectroscope. 
Thedark purple forms of chloride do not give as good results 
as the rose and coppery shades. These last have many points 
of resemblance with the material of Becquerel’s films, resem- 
blance of color, probably of composition, as far as we can 
judge of the constitution of those films from their origin ; they 
were far too attenuated to admit of analysis; and resemblance 
in the curious way in which their color is affected by heat, so 
that the conclusion seems inevitable, that they are at least 
closely related. 
There is certainly here a great and most interesting field for 
experiment; hardly any two specimens of photochloride give 
exactly the same results with colored light, and this suggests 
great possibilities. There is the very great advantage in this 
method over any previous, that the material is easily obtained 
in any desired quantity and in a condition most favorable for 
experiment. 
