480 MM. C. Lea—Identity of the Photosalts of Silwer 
Coutchiching. 
Laurentian. 
With reference to their age, as follows: 
Keweenawan (Nipigon). 
Huronian (Animikie). 
Diabase dykes and gabbro. 
Granite, post-Laurentian. 
Laurentian. 
Keewatin. 
Coutchiching. 
.Petrographical Laboratory, Johns Hopkins University, March, 1887. 
Art. XLVII.—Jdentity of the Photosalts of Silver with the 
Material of the Latent Photographic Image; by M. Carny 
Lea, Philadelphia. 
In the first part of this paper I described certain strongly 
colored forms of silver chloride, bromide and iodide, obtained 
independently of any action of ‘light, for which I proposed the 
name of photosalts, “by reason of their identity with the pro- 
ducts of the action of hght on the normal silver haloids; both 
with the substance of the latent image itself and also with the 
principal results of the continued action of light on these ha- 
loids. It remains to prove this identity. 
First as to identity with the product of the continued action 
of light. 
Ti we expose silver chloride precipitated with excess of HCl 
to light, we get a deep purple black substance which boiled 
with dilute nitric acid gives up a little silver, at the same time 
somewhat lightening in color and forming a dull purple ma- 
terial which closely resembles some of the forms of photo- 
chloride described in the first part of this paper, most those pro- 
duced by the action of sodic hypochlorite or of ferric chloride 
on metallic silver: it shows the same reactions with ammonia 
that they do. The brighter colored photochlorides are not 
formed by the action of light on silver chloride. 
But these brighter colored chlorides can also be shown to 
be formed through the action of hght. Most salts of silver 
darken by exposure, and when these dark products are treated, 
first with HCl, and then after thorough washing, are boiled 
with dilute nitric acid, we can obtain results perhaps as varied 
as those which I described in the former part of this paper as 
arising from purely chemical action. 
Silver oxalate exposed for two days to sunshine, covered with 
water and with frequent agitation, changed to a deep brownish 
