ME. GEOEGE GOEE ON ELUOEIDE OE SILYEE. 
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placed in a platinum cup -51 millims. deep and 10 millims wide, and evaporated to dryness 
and heated to gentle fusion, left 66T6 grains of solid residue. After allowing *34 grain 
for the fluorine set free during the fusion, the result shows that 6 6 ‘5 parts of it dissolved 
in 37‘08 parts of water, or 1 part of water dissolves about 1*79 part of the salt at 
15°*5 C., or 1 part of the salt is soluble in *55 part of water at that temperature. The 
aqueous solution is strongly alkaline to litmus-paper. On adding distilled water to a 
hot saturated solution, a white cloud appeared which afterwards dissolved ; it probably 
consisted of a basic salt. On several occasions I have had reason to suspect a slight 
degree of solubility of finely divided metallic silver in a strong solution of the salt, 
similar to that of lead and silver in strong aqueous solutions of their respective nitrates. 
The salt is nearly insoluble in anhydrous alcohol. 
By weighing a known amount of the brown salt in a specific-gravity bottle filled up 
with tetrachloride of carbon, the specific gravity of it was found to he =5 - 852 at 1 5°*5 C. 
The saturated solution of it at 15° - 5 C. was very heavy, its specific gravity being 
= 2 , 61. I have not obtained crystals from it at that temperature*, but by placing it 
in a covered platinum cup in a freezing-mixture at — 23 0, 5 C. it solidified to a mass of 
needle-shaped crystals, radiating towards the centre of the cup, and finally to a solid mass 
of colourless salt with deep fissures in its surface produced by contraction. In another 
similar experiment the solution became a mass of crystalline plates at — 2 0, 25 C., very 
similar to those of the acid fluoride of potassium. During the formation of these 
crystals a yellowish-brown sediment formed at the bottom of the vessel, and on dissolving 
the crystals by means of gentle heat the sediment remained. The crust was now broken 
to pieces, and a little cold water added ; this caused it to cohere to a rather hard mass, 
which soon dissolved to a colourless liquid, leaving only a few blackish particles. 
There was no impurity present, and the probable explanation of the formation of the 
crust is that there was not sufficient water in the original solution to form the crystal- 
line hydrate, and when the hydrate crystallized it withdrew the water from the remain- 
ing portion of salt, and left it in the anhydrous state as a heavy powder which sank to 
the bottom. This result is remarkable if we consider the great degree of attraction for 
water which the anhydrous salt possesses, and shows that its tendency to form a crystalline 
hydrate is even more powerful. I have not experimentally determined the composition 
of the crystals, but from several circumstances I consider them likely to prove penta- 
hydrated. A saturated solution of the salt chilled to — 18° C. exhibited the pheno- 
menon of supersaturation on immersing a platinum wire in it. Melted fluoride of silver 
which had been gradually cooled was covered with crystalline markings. 
A fragment of the brown salt in a well-stoppered colourless glass bottle, exposed to 
daylight and sunlight during ten weeks, showed no signs of decomposition. A satu- 
rated solution of the salt in a platinum cup in a similar bottle similarly exposed during 
fourteen days evolved traces of hydrofluoric acid, but liberated no silver. 
* According to Fremy, ‘ Chemist,’ New Series, vol. i. pp. 556 & 557 ; Comptes Eendus, February 27, 1854. 
a concentrated solution of the salt yields very regular crystals. 
2 h 2 
