﻿Mr. G. Gore on Fluoride of Silver. 309 



local attraction at stations on the arc of meridian and out at sea (in 

 Minicoy, an island 250 miles west of Cape Comorin or Punnoe) ; for 

 the sensible negative quantity at Damargida and positive quantity at 

 Kalianpur indicate a deficiency of matter below the first and an 

 excess below the second, which exactly tally with the results inde- 

 pendently brought out by relative deflections of the plumb-line as 

 obtained by the survey : and the two large and most important effects, 

 negative at Kaliana and positive at Minicoy, may be said to be almost 

 annihilated by this method of correction. This last case of an excess 

 of gravity out at sea (where the surrounding ocean has a deficiency 

 of matter) being explained by his method he regards as a very strong 

 argument in its favour. And he finishes by saying that if his me- 

 thod is thus far successful in the particular supposition of the dis- 

 tribution below, whether in excess or defect, being uniform, which 

 is most likely not strictly the case, there is every reason for con- 

 cluding that pendulum- observations give support to the hypothesis 

 regarding the Constitution of the Earth's Crust, when viewed on a 

 large scale, admitting of local peculiarities, like the deficiency of 

 matter near Damargida and the excess near Kalianpur, and the 

 similar deficiency near Moscow. 



January 12, 1871. — General Sir Edward Sabine, K.C.B., President, 

 in the Chair. 



The following communications were read : — 



"On Fluoride of Silver."— Part II. By George Gore, F.R.S. 



This paper contains an exhaustive account of the behaviour of 

 argentic fluoride in vessels of platinum, carbon, and various fluo- 

 rides in contact with chlorine, bromine, and iodine at various tempe- 

 ratures. "When argentic fluoride is completely decomposed by chlo- 

 rine in platinum vessels at a red heat, the reaction agrees with the 

 following equation : 



4AgF+4Cl+Pt=4AgCl, PtF 4 . 



"Vessels of cryolite and of fluor-spar were found incapable of re- 

 taining argentic fluoride in a melted state. Other vessels were also 

 made by melting and casting various mixtures of earthy fluorides at a 

 high temperature ; and although forming beautiful products, pro- 

 bably capable of technical uses, they were not capable of retaining 

 silver fluoride in a state of fusion. Numerous vessels were also made 

 of seventeen different fluorides by moulding them in the state of clay 

 and baking them at suitable temperatures; these also were found 

 incapable of holding melted fluoride of silver. Argentic fluoride was 

 only superficially decomposed by chlorine at 60° Fahr. during thirty- 

 eight days. When heated to 230° Fahr. during fifteen days in a 

 platinum vessel in chlorine, it was very little decomposed. Chloride 

 of silver heated to fusion in a platinum vessel in chlorine corroded 

 the vessel and formed a platinum-salt, as when fluoride of silver was 

 employed. 



An aqueous solution of argentic fluoride agitated with chlorine 

 evolved heat and set free oxygen, in accordance with the following 



Phil Mag. S. 4. Vol. 41. No. 273. April 187] . Y 



