the Chloride, Bromide^ and Iodide of Silver. 289 



than the chloride, and more than twice as well as the iodide. We should 

 naturally expect the iodide from its comparatively loose crystalline nature 

 to conduct heat less well than either the bromide or chloride. 



4. Effects of Heat on the Bromide of Silver. 



Precipitated bromide of silver was fused, and cast in warm glas& 

 tubes. The mass when warm was found to be somewhat tenacious ; the 

 surface of the fused rod was smooth and brilliant, the fracture crystal- 

 line. Bepeated fusion seemed to render the substance more crystalline. 

 Although crystalline the substance was very compact, and altogether un- 

 like the crystalline condition of the iodide ; the rod contracted a good 

 deal in cooling, and easily came out of the tube in which it was fused. 

 Eods 6 inches long by 5 inch diameter had their ends levelled by means 

 of a fine steel saw, and were placed in the expansion-apparatus, and 

 tested as described in the case of the iodide bars. The coefficient of 

 cubical expansion for 1° C. was found to be 



•00010500. 



Fizeau by his optical method found the coefficient to be •000104061. 

 The coefficient increases with the temperature, at least to the extent of 

 •000004 for each 100° C. increase of range. The expansion is very con- 

 siderable in passing from the solid to the liquid condition, and between 

 380° (which I believe to be near its melting-point) and a temperature esti- 

 mated at 750° 0. The volume at — 60° C. has been taken as unity in 

 order for better comparison with the iodide in the accompanying Curve 

 Table (p. 290), and an addition of -000004 to the coefficient has been made 

 for each 100° C. of temperature. Then if we suppose a^ molten mass of 

 bromide of silver to be cooling down from 750° C. to — 60° C, the fol- 

 lowing is an approximation to the volumes of the mass at the various 

 temperatures indicated : — 



Volume at 750 C = 1-167940 



„ 380 (Hquid) = 1-122840 



„ 380 (soHd) = 1-048120 



,,300 = 1-038760 



„ 200 = 1-027460 



„ 100 = 1-016560 



„ „ = 1-006060 



,,-60 = 1-000000 



The specific gravity at 7° C. was found to be 6-245 in the case of a 

 specimen which had been often fused, and 6-293 in the case of a speci- 

 men which had been only once fused. This would give 5-595 as the 

 sp. gr. of the molten bromide at the fusing-point. 



