on some Chloro-brom-iodides of Silver. 



293 



iodide of silver in one another. Such bodies are found native : emholite 

 {en^oXiov) is a chloro-bromide of silver in which the ratio of the chloride 

 to the bromide varies indefinitely. Minerals having respectively the 

 composition Agg Br Q\, Agg Br^ CI3, Ag^ Brg CI, Agg Br^ CI-, and Ag^ Br 

 CI3 have been analyzed by Domeyko, Pield, Miiller, Eichter, and 

 others. They occur chiefly in Chili, and constitute the principal ore of 

 the silver-mines of Chanarcillo. They are described as possessing specific 

 gravities which vary between 5*75 and 6*2 ; and according to Dana the 

 colour is " greyish green, and asparagus-green to pistachio or yellowish 

 green, and yellow ; often dark, becoming darker externally on exposure." 

 Dana further states that an iodobromide of silver is found native in 

 Chili ; but of this I am unable to find any description. 



In examining the following results, we must bear in mind that we are 

 dealing with bodies which are very differently affected by heat. For 

 while the chloride and bromide of silver have higher coefficients of ex- 

 pansion than the most expansible metals (such as zinc), the iodide of silver 

 contracts slightly when heated to a temperature of 142° C, while between 

 142° and 145°-5 C. it undergoes considerable contraction ; then expands 

 to the melting-point, undergoes considerable increase of volume in pass- 

 ing from the solid to the liquid condition, and expands slightly beyond 

 this temperature and the melting-point. Moreover the iodide passes 

 into an amorphous condition between 142° C. and 145°-5 C, and possesses 

 a point of maximum density at 142° C. The following volumes are 

 given for comparison with those of the alloys (the coefficients for both 

 the bromide and chloride are not given because they are practically the 

 same, and one serves for both) : — 



Bromide of Silver. 

 ° 0. Volume. 



At 750 = 1-167940 



380 (Hquid)... = 1-122840 

 383 (solid) ... = 1-048120 



300 = 1-038760 



200 = 1-027460 



+ 100 = 1-016560 



= 1-006060 



- 60 = 1-000000 



Iodide of Silver. 

 ° 0. Volume. 



At 750 (liquid) = 1-052946 



450 (liquid) = 1-044990 



450 (soHd) = 1-008659 . 



142 (max. density) = TOOOOOO 

 145-5 (aft. sudden ex.)= 1-015750 

 + 70 = 1-017009 



- 10 = 1-017342 



- 60 = 1-017394 



Contraction 

 on cooling, 

 expansion 

 on heating. 



Expansion 

 on cooling, 

 contraction 

 on heating. 



The alloys were examined in the same manner as I have previously de- 

 scribed in determining the coefficients of expansion of their constituents*. 



They were cast into rods 8 inches long by 5 to § inch diameter in warm 

 glass tubes ; then by means of a fine steel saw they were cut into lengths 

 of 6 inches, and examined in the expansion-apparatus described and 



■On the Effects of Heat on the Chloride, Bromide, and Iodide of Silver," see ante, 



