236 
ME, GEOEGE GOEE ON FLUOEIDE OF SILVEE. 
tion of the salt at ordinary temperature: — aluminium, magnesium, silicon, iridium , 
rhodium , and carbon of lignum-vitce nearly equal, platinum, palladium, tellurium*, gold. 
The iridium was much more strongly positive if it was covered with a film of oxide. 
Chemical Behaviour. 
In many of the experiments great corrosion and injury of the vessels was caused by 
reduced silver alloying with the platinum ; and the products of the reactions were very 
difficult and tedious to remove. The solvents employed for cleaning the vessels were 
usually dilute nitric or hydrochloric acids, strong aqueous ammonia, or saturated solu- 
tions of iodide of potassium or nitrate of mercury f. In some cases the residue of silver- 
salt had to be reduced to metal at a red heat by means of hydrogen or alkaline carbonates. 
With Hydrogen. — The reduction of the salt by hydrogen has been already described 
(Phil. Trans. Hoy. Soc. 1869, p. 183). Fragments of the brown salt in hydrogen in a 
colourless glass vessel at 60° Fahr., exposed to sunlight during two days, exhibited no 
chemical change. A solution of the salt in a platinum vessel at 60° Fahr., containing 
a little free hydrofluoric acid, was not decomposed by passing a stream of hydrogen 
through it. 
With Nitrogen. — A globe of glass of the form A, fig. 6, was 
filled with pure nitrogen; the platinum retort B enclosing a 
platinum boat, containing a weighed amount of the previously 
fused salt, was now fixed on air-tight by means of a washer of 
vulcanized india-rubber at C, and its outer end heated to redness 
during half an hour, the mouth of the vessel being closed air- 
tight by a bung of vulcanized india-rubber, and immersing it in 
a basin of mercury. On opening the mouth of the cooled vessel 
under mercury, no alteration of volume of the gas was found, and the loss of weight of 
the boat and its contents was only -26 grain. The residual gas was found by proper tests 
to be nitrogen. Nitrogen, therefore, is not absorbed by, and does not decompose, 
argentic fluoride at a low red heat. 
With Ammonia. — A fragment of the brown salt, weighing 104 grains, was fixed in an 
iron clip and introduced into a colourless 4-ounce bottle filled with dry ammonia gas 
over mercury, a stick of caustic potash having been previously placed in the gas ; the 
bottle was then exposed to sunlight. In a few minutes the salt became darker in colour, 
and a slow absorption of the gas continued during about twenty-six days ; a slight odour 
of ammonia then remained, and the salt had absorbed about 98'3 cub. centims. or T0914 
grain, or about 844 times its volume of the gas. Light was not necessary, as the ab- 
sorption was observed to occur during the night. The ammoniated salt was odourless, 
and was probably analogous to the corresponding compound of argentic chloride and 
* The tellurium contained traces of copper. 
f The most convenient plan I have employed for recovering noble metals from the acid liquids used in clean- 
ing the pieces of apparatus, has been to immerse a plate of zinc in them in a vessel of ebonite. 
