[ 1125 ] 
XXVI. On the Effects of Ileat on certain Haloid Compounds of Silver, Mercury, 
Lead, and Copper. 
By G. F. Rod well j Science Master in Marlborough College. 
Communicated by Professor A. W. Williamson, For. Sec. R.S. 
Received November 11,—Read December 8, 1881.* 
[Plate 96.] 
Contents. 
Page. 
1. Introduction . 1125 
2. Method of research and apparatus employed. 1126 
3. Iodide of silver, Agl . 1133 
4. Bromide of silver, AgBr . 1137 
5. Chloride of silver, AgCl . 1138 
6. Chlorobromiodides of silver, having the composition:—Agl, Ag 2 Br 3 , Ag 3 Cl 2 ; 
Agl, AgBr, AgCl; Ag 2 I 2 , AgBr, AgCl; Ag 3 T 3 , AgBr, AgCl; Ag 4 I 4 , 
AgBr, AgCl. 1140 
7. Di-iodide of mercury, Hgl 3 . 1141 
8. Iodide of lead, Pbl 3 . 1144 
9. Lead-silver iodide, PbI 3 .AgI . 1146 
10. Iodide of copper, Cu 2 I 2 . 1151 
11. Copper-silver iodides, having’ the composition:—Cu 2 I 2 .AgI; Cu 3 I 3 .2AgI; 
Cu 2 I 2 .3AgI; Cu 2 l 3 .4AgI; Cu 3 I 3 .12AgI . 1154 
12. Discussion of the results. 1160 
1. Introduction. 
The researches described in the following pages, which were commenced in 1874, were 
suggested by observations made by Professor Clerk Maxwell and M. Fizeau. The 
former (‘ Theory of Heat/ p. 8), in discussing the effects of heat upon matter, 
writes : “ The body generally expands (the only exception among solid bodies, as far 
as I am aware, is iodide of silver, which has been found to contract as the tempera- 
* The author has been engaged at intervals during the last five years on an investigation of the effect 
of heat in producing expansion and contraction in iodide of silver and some other allied iodides and their 
alloys. A series of papers on the subject, written as the results were successively got out, have been 
published in the Proceedings of the Royal Society. 
The paper which forms the last of the series, and which contains the results obtained with an extended 
series of alloys, by the methods which were ultimately adopted as the best, was read before the Royal 
Society on December 8, 1881, and an abstract only of it has appeared in the Proceedings, The present 
memoir is made up of the paper in question, preceded by a general account of the whole investigation. 
