284. Dr. W. Gregory on a new method 
silver. By converting the silver into the insoluble chloride, 
it is effectually purified from copper as well as from all other 
metals, the chlorides of which are soluble. But here the 
difficulty begins : the chloride of silver is a very unmanageable 
product, at least in the moist way. It is true that if placed in 
water acidulated with hydrochloric acid, in contact with zinc 
or iron, the chloride of silver is reduced. But the process is 
tedious, seldom complete, and in the end unsatisfactory; for 
some zine adheres to the reduced silver, so that it is not re- 
moved by digestion with moderately strong hydrochloric acid. 
This is proved by the action of ammonia, which extracts a 
good deal of oxide of zinc. Moreover, the zinc or iron is 
hardly everpure ; and its impurities, arsenic, carbon, and per- 
haps also copper and tin, remain with the silver. I have never 
got from silver thus reduced, a colourless solution of nitrate. 
It is no doubt better to decompose the dried chloride of 
silver by the action of carbonate of potash or soda at a red 
heat. But although the silver is thus obtained pure, the pro- 
cess requires much experience and dexterity. If the heat be 
too low, the reduced silver is disseminated in small globules 
through the mass; if too high, the alkali corrodes the crucible 
rapidly, and the contents fall into the fireplace or ash-pit. 
There is often also a portion of silver cast up by the effer- 
vescence on the sides of the crucible, in small globules, which 
do not readily run down into the fused mass below. Inshort, 
this process, always ticklish, often fails. It is therefore de- 
sirable, if possible, to dispense with a furnace heat. 
The method of reducing the silver from the impure nitrate 
by protosulphate of iron does not answer. It is long ere the 
action is terminated, and besides, some sulphate is always 
formed, which zs not reduced, and is partly precipitated with 
the metal, and partly retained in solution. 
The only remaining method, known to me, is that of re- 
ducing the silver from the impure (cupreous) nitrate or sul- 
phate, by means of copper. The chief objection to this method 
is that it is somewhat tedious; but it is also not improbable 
that a trace of copper may adhere to the silver, chemically 
combined, as is the case to a large extent with mercury in 
the Arbor Diane. At least I have generally found copper 
in the silver I have thus prepared. 
Considering these things, it appeared desirable to have 
once more recourse to the chloride, which can be easily ob- 
tained perfectly pure, and to decompose it without the con- 
tact of any reguline metal. The most obvious plan was to 
try the action of caustic alkalies in the moist way, and although 
it has been singularly enough hitherto overlooked, I find that 
caustic potash may be used with complete success. Diluted 
