THE 
AMERICAN JOURNAL OF SCIENCE, 
[THIRD SERIES] 
— = - Amor, 
od 
5 a ae 
Art. XXXVI.—On Red and Purple Chloride, Bromide and 
Todide of Silver; on Heliochromy and on the Latent Photo- 
graphic Image; by M. Carry Lea, Philadelphia. Part I. 
In this series of papers it will be my object to show: 
(1.) That chlorine, bromine and iodine are capable of form- 
ing compounds with silver exhibiting varied and beautiful col- 
oration, peach-blossom, rose, purple and black. That these 
compounds (except under the influence of light) possess great 
stability: that they may be obtained by purely chemical means 
and in the entire absence of light. 
(2.) That of these substances the red chloride shows a tend- 
ency to the reproduction of colors. It seems not improbable 
that the material of the infinitesimally thin films obtained by 
Becquerel, Niepce de St. Victor, Poitevin and others in their 
experiments on heliochromy may be the red chloride. 
(3.) That these substances, formed by purely chemical means, 
constitute the actual material of the latent or invisible photo- 
graphic image, which material may now be obtained in the 
laboratory without the aid of light and in any desired quan- 
tity.. They also form part of the visible product resulting 
from the action of light on the silver haloids. 
For more than a generation past, the nature of the latent 
photographic image, that which forms the basis of development, 
has been in dispute. Two theories have been maintained. 
Am. Jour. Sci1.—Tuirp Suries, VoL. XXXIII, No. 197.—May, 1887. 
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