M. 0. Lea—Chloride, Bromide and Lodide of Silver. 355 
make a solution of any other silver salt in ammonia and reduce 
it in the manner just described with ferrous sulphate. But in 
this case hydrochloric acid must be used instead of sulphuric 
after the reduction. This single reaction includes an almost 
endless variety of methods. The acid with which the silver 
was originally combined seems to be not without influence on 
the result; in some cases, for example, with arseniate and 
molybdate, the action of colored light on the red chloride seems 
to be somewhat modified. Silver phosphate on account of the 
ease with which it suffers reduction is very well adapted for 
this treatment. ; 
Photochloride by Partial Reduction of Oxide by Heat, and 
Treatment with HCl. 
This method has the advantage of avoiding all admixture of 
foreign substances, the last traces of which are very hard to get 
rid of, and seem to-exert an effect on the color disproportionate 
to their quantity. Accordingly the photochloride obtained in 
this way is very beautiful, the shades are from pink to copper 
red, and a tint resembling burnt carmine. 
Heat may be applied to the oxide in either of two ways, 
long continued heat at 212° ’., or near it; or the change may 
be effected by roasting. 
When slow heat is to be applied care must be taken that the 
oxide does not carbonate itself, which it easily does superficial- 
ly ; this is an objection because the carbonate, under these cir- 
cumstances yields white chloride with which the other becomes 
mixed. The air of a drying oven heated by a gas burner is 
especially bad in this respect. I have seen a surface of oxide 
form a coat of yellow carbonate in a few hours in this way. 
(Most oxide that has been kept sometime will effervesce briskly . 
with an acid.) The method is uncertain, sometimes giving ~ 
strongly colored products and sometimes pale pink. 
The oxide may be roasted in a shallow flat-bottomed por- 
celain basin. With a very moderate heat it changes from 
brown to black. When this is thoroughly accomplished and 
before gray reduction sets in, the oxide is to be treated with 
HCl. If this be done in the basin itself after cooling and with- 
out disturbing the position of the oxide, a curious variety of 
tints will be noticeable, depending upon slight differences in 
the heat affecting different portions. 
Silver Carbonate may be roasted in the same way as silver 
oxide, and yields a similar product. By heat its color changes 
from yellow to black; it is probable that the carbonic acid is 
driven off at a lower temperature than that at which oxide is 
reduced to silver, and that with it escapes part of the oxygen. 
The residue is converted by HCl into deep red chloride. 
