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XII. On Fluoride of Silver. By George Gore, F.B.S. 
Received October 5, I860,- — Read January 13, 1870. 
Formation* . 
Anhydrous or gaseous hydrofluoric acid had no visible action on metallic silver ; by 
electrolysis of the aqueous acid with a silver anode, the metal was dissolved and argentic 
fluoride formed ; by electrolysis of anhydrous hydrofluoric acid also, a silver anode was 
rapidly corroded. Metallic silver in contact with platinum, in a mixture of dilute hydro- 
fluoric acid and aqueous nitrate of potassium, was not corroded even with the aid of heat. 
A solution of nitrate of silver, mixed with dilute hydrofluoric acid, did not yield fluoride 
of silver on evaporation to dryness ; nor did it show any signs of decomposition on the 
addition of solutions of any of the soluble fluorides, except stannous fluoride, or a satu- 
rated solution of fluoride of potassium. The effects of anhydrous hydrofluoric acid 
upon oxide, peroxide, nitrate, chloride, iodide, and carbonate of silver have been already 
briefly described (Phil. Trans. Hoy. Soc. 1869, pages 191 and 192). 
Preparation. 
I prepared the salt as follows : — A solution of pure nitrate of silver was precipitated 
by pure carbonate of sodium, and the well-washed carbonate dissolved in dilute hydro- 
fluoric acid ; a little heat was absorbed. The clear liquid was heated to boiling, filtered, 
evaporated, and heated to incipient fusion ; transferred whilst hot to a bottle of platinum, 
and when partly cool retransferred to a gutta-percha bottle. 
The earthy-brown salt thus prepared contains a small amount of free silver (espe- 
cially if it has been stirred when nearly dry), some water, and traces of hydrofluoric 
acid. To remove the water and acid, I have sometimes heated it in a platinum cup 
covered with layers of filtering-paper kept cold by a vessel of water placed upon them. 
When nearly dry it had a greenish metallic lustre, due to the free silver ; and when 
made perfectly anhydrous, by heating nearly to its point of softening, it was black, with 
a grey satin metallic lustre. 
Analysis. 
To determine the amount of silver, I passed hydrogen, steam, or ammonia over the 
gently fused salt, or I precipitated the aqueous solution by hydrochloric acid. To find 
the amount of fluorine, I precipitated the solution by nitrate of lime; I also employed 
the following process, and found it much more accurate and satisfactory. About 50 or 
100 grains of the salt was weighed in a narrow closed cup of platinum, the cup then 
* All the operations upon fluorine compounds described in this paper were conducted in platinum vessels, 
unless otherwise stated. 
