1870.] 



Mr. G. Gore on Fluoride of Silver. 



157 



The specific gravity of the granular mineral is 3*198, and its hardness 

 5-5. 



The result of the above analyses is to show that, except for a little 

 chromite and a little augite, with possibly in the crystallized mineral a 

 little free silica, both that mineral and the collective silicate of the stone 

 consist of a ferriferous enstatite. 



The formula most in accordance with the analysis would be 

 (| MgiFe)0, Si0 2 ; 

 that of the enstatite in the Breitenbach meteorite is (f Mgi Fe)0, Si0 2 . 



The bulk of the Busti meteorite consists of a purely magnesian enstatite; 

 this of Manegaum is almost entirely an enstatite richer in iron than any 

 yet examined. Both bear evidence to the white flocculent mineral which 

 characterizes the microscopic sections of many meteorites, being composed 

 of this now important mineral enstatite. 



In publishing the results I have obtained in the attempt, so far as this 

 memoir goes, to treat exhaustively of the mineralogy of two important me- 

 teorites, I wish to record the obligations I am under to Dr. Flight, Assis- 

 tant in my Department at the British Museum, for his valuable aid in the 

 chemical portion of the inquiry. 



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

 Received October 5, 1869. 



(Abstract.) 



This communication treats of the formation, preparation, analysis, com- 

 position, common physical properties, and chemical behaviour of fluoride 

 of silver. 



The salt was prepared by treating pure silver carbonate with an excess 

 of pure aqueous hydrofluoric acid in a platinum dish, and evaporating to 

 dryness, with certain precautions. The salt thus obtained invariably con- 

 tains a small amount of free metallic silver, and generally also traces of 

 water and of hydrofluoric acid, unless special precautions mentioned are 

 observed. It was analyzed by various methods : the best method of deter- 

 mining the amount of fluorine in it consisted in evaporating to dryness a 

 mixture of a known weight of the salt dissolved in water, with a slight 

 excess of pure and perfectly caustic lime in a platinum bottle, and gently 

 igniting the residue at an incipient red heat until it ceased to lose weight. 

 By taking proper care, the results obtained are accurate. The reaction 

 in this method of analysis takes place according to the following equation, 

 2AgF + CaO = CaF 2 + 2Ag + 0. Sixteen parts of oxygen expelled equal 

 thirty-eight parts of fluorine present. One of the methods employed for 

 determining the amount of silver consisted in passing dry ammonia over 

 the salt in a platinum boat and tube at a low red heat. The results ob- 



