M. C. Lea—Chloride, Bromide and Iodide of Silver. 351 
first named explanation as the true one. When the red chlo- 
ride, for example, has been boiled with dilute nitric acid for a 
few moments to eliminate any uncombined subchloride, the 
proportion of subchloride left has never exceeded 8 or 9 per 
cent in over thirty specimens analyzed. If we took this to 
represent a compound in equivalent proportions, we should 
have to suppose the union of at least twenty equivalents of 
AgCl with one of Ag,Cl, which is improbable. If we suppose 
that these colored substances containing from less than one-half 
per cent up to eight or nine per cent of Ag,Cl consist of a com- . 
pound of one equivalent of subchloride united to asmall number 
of equivalents of normal chloride, mixed mechanically with a 
large quantity of normal chloride, then it would be improbable 
that specimens could not be obtained containing a larger pro- 
portion of this compound and consequently of Ag,Cl, but as 
already said, specimens containing more than 9 per cent after 
thorough treatment with nitric acid to remove the uncombined 
subchloride I have never obtained: generally the amount is 
less. aa 
Even when silver chloride, bromide or iodide contains as 
little as one-half of one per cent of subsalt combined, its prop- 
erties are greatly changed. It has a strong coloration and its 
behavior to light is altered. Hven a much less quantity, one 
inappreciable to analysis, is capable of affecting both the color 
and the behavior to light. 
It is one of these latter forms of this substance that consti- 
tutes the actual material of the latent photographic image: 
adequate proof of this will be given in the second part of this 
paper. 
Rep SinvER CHLORIDE. 
Of the three haloids, the chlorine salt is the most interesting, 
because of its relations to heliochromy; it is also the most 
stable of the three compounds and exhibits perhaps a finer 
variety of coloration, though the bromide and iodide are also 
obtainable of very beautiful tints. The chloride shows all the 
warm shades from white to black through the following grada- 
tions: white, pale flesh color, pale pink, rose color, copper 
color, red purple, dark chocolate, black. 
These compounds are obtained in an endless variety of ways: 
by chlorizing metallic silver; by acting on normal chloride 
with reducing agents; by partly reducing silver oxide or silver 
carbonate by heat and treating -with HCl; by forming suboxide 
or a subsalt of silver and treating with HCl followed by nitric 
acid; by acting on subchloride with nitric acid or an alkaline 
hypochlorite, etc.; by attacking almost any soluble salt of 
silver with ferrous, manganous or chromous oxide, etc., fol- 
