293 Mr. G. F. Rodwell on the Effects of Heat 



On the Effects of Heat on some Chloro-brom-iodides of Silver/' 

 By G. F. Rodwell, F.R.A.S., F.C.S., Science Master in Marl- 

 borough College. Communicated by Frederick Guthrie, 

 F.R.S., Professor of Physics in the Royal School of Mines. 

 Received April 13, 1876-^. 



In a recent communication to the Society I have given the approximate 

 coefficients o£ expansions of the chloride and bromide of silver, and the 

 coefficients of contraction and expansion of the iodide of silver. It was 

 thought that some interesting results might be obtained by alloying 

 these bodies together, and thus forming various chloro-brom-iodides of 

 silver, and by investigating the physical properties of such bodies and 

 the effects of heat upon them. Accordingly these bodies were fused 

 together in the proportions requisite to form the following com- 

 pounds : — 



Ag I, Ag, Br„ Ag, CI,. 



Ag I, Ag Br, Ag CI. 



Ag, I„ Ag Br, Ag CI. 



Ag3 I3, Ag Br, Ag CI. 



Ag, I„ Ag Br, Ag CI. 

 Dr. Matthiessen (" On Alloys," Chem. Soc. Journ. 1867, p. 201) states 

 that he believes " in nearly all cases the two metal alloys may be considered 

 as solidified solutions of the one metal in the other ; " and he continues 

 as follows : — " By the term solidified solution I mean a solution of two 

 substances which has been allowed to solidify, as, for instance, if a mix- 

 ture of ether and alcohol were made, and sufficient cold could be produced 

 to soHdify it, we should produce a soHdified solution of these two sub- 

 stances in one another. Again, if the chlorides of potassium and 

 sodium, say in equal parts, be melted together and allowed to sohdify, 

 the solid thus produced is a soHdified solution of the chlorides of 

 potassium and sodium in one another. Glass is also a good example 

 of a sohdified solution ; to produce it, different siUcates are fused together 

 and allowed to soHdify. There is, however, an important point in the 

 definition of the term 'sohdified solution' which must not be over- 

 looked — namely, that the components are most intimately mixed to- 

 gether ; in fact they are homogeneously diffused in one another, and to 

 that extent that, even in the most powerful microscope, it would not be 

 possible to distinguish the components of a solidified solution. As 

 examples of this fact glass may be quoted, which presents under high 

 magnifying-power a homogeneous mass ; the silver and gold in the 

 gold-silver aUoys cannot be distinguished by the same test from one 

 another." 



Accepting Dr. Matthiessen's definition, we must regard the chloro- 

 brom-iodides of silver as solidified solutions of chloride, bromide, and 

 * Read May 4, 1876, See ante, p. 4. 



