M. C. Lea— Reactions of Silver Chloride and Bromide. 191 
When cold nitric acid, sp. gr. 1:28, is poured over a goansity 
C 
quickly whitened by aqua regia, it is reasonable to conclude 
that the dark matter contain less chlorine than the normal, 
and is either a subchloride or an oxychloride. Beyond this, 
we know nothing with certainty 
When the dark substance was boiled for several minutes 
with the same nitric acid, no silver was extracted. But when 
the vessel was placed on a sand bath and kept at or near boiling 
point for eighteen hours, renewing the acid as it escaped, a dis- 
tinct effect was produced. The substance became a little lighter 
in color, and the acid was found to have taken up enough sil- 
ver to show a strong opalescence by addition of hydrochloric 
acid ; not enough however to give an immediate precipitate. 
monia and sodium hyposulphite have this in common, 
that both leave metallic salien behind when the darkened 
chloride is submitted to their action. In the case of the sodium 
salt, it is of course understood that it is presented in strong 
solution and very large excess. 
Silver Bromide. 
Silver bromide was precipitated with excess of KBr and 
well washed, and exposed to light. 
When cold nitric acid, sp. gr. 1°28, was allowed to stand for 
‘One minute over the darkened bromide it took up silver abun- 
dantly. Allowed to act for an hour at a heat considerably be- 
low 212° the color of the darkened bromide had considerably 
changed and at the end of seven or eight hours, com plete decom- 
position had taken place. The resulting AgBr is lemon yellow 
and has more the general appearance of iodide than of bromide. 
Philadelphia, Jan., 1878. 
influences. To a considerable on this v 
substitution of gold for the metallic silver. < 
The use of a fixi “reatment can of course never be dispensed as it is 
essential to remove the unaltered chloride. But it is evident that if a substance 
sage be found which would remove the te : chlo mechs nega reg 
wh by li a great advan 
ing that which has been da pores fem ti  apgardiaggir: Ges 
Stopped when the right strength was obtained, without being 
allow for nite effect sf the fixing agent, and the print obtained w 
probabl: be alwa: perfectly permanent. ~ ee : 
The fact that both sodium ky posulphite and ammonia in removing the unaltered 
chloride, reduce the altered to metallic silver, explains why the gold toning opera- 
tion succeeds much better when applied after the fixing operation, than before it. 
