1881.] Effects of Heat on the Chloride, tyc, of Silver. 291 



fore its temperature, could not be found. But since the calorimeter 

 had slightly risen in temperature, the ice must have been above 80° C. 



From the nature of the experiment, as carried out on the present 

 scale, the weight of the ice which can be dropped into the calorimeter 

 is only small, and therefore the rise in temperature is but slight. But 

 since a fall in temperature of a much larger amount ought to have 

 been obtained had the ice been at 0°, it is considered that the above 

 experiments are conclusive. Great care was taken, in order to obtain 

 correct temperatures in the calorimeter. The latter was inclosed in 

 several casings, and the water was allowed to stand in it for several 

 hours before the experiment, so that it might first attain the tempera- 

 ture of the room, whilst the time which elapsed between the readings 

 of the thermometer before and after the ice was dropped in would not 

 be more than from 10 to 15 seconds. 



In the course of the next few weeks I intend to make one or two 

 more determinations, and, if possible, on a larger scale. 



V. " On the Effects of Heat on the Chloride, Bromide, and 

 Iodide of Silver, and on some Chlorobromiodides of Silver." 

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

 Marlborough College. Communicated by Professor Tyn- 

 dall, F.R.S, Received November 26, 1880. 



1. The Chloride, Bromide, and Iodide of Silver. 



Since I had the honour of submitting to the Society papers on the 

 above subjects, " Proc. Boy. Soc," vol. 25, p. 279 — 303, accurate 

 determinations, by a new method, of the melting points of the sub- 

 stances with which the experiments were made have been described 

 by Mr. Carnelley. He finds that the melting point of iodide of silver, 

 hitherto generally described as "a low red heat," is 527° C. ; of the 

 bromide of silver 427° 0. ; and of the chloride 451° C. These num- 

 bers are in all cases higher than those which I adopted, and I have, 

 consequently, recalculated those portions of the results which are 

 affected by the new determinations, and they are given in the follow- 

 ing table. The volume of the chloride and bromide at — 60° C. has 

 been taken as unity for better comparison with the iodide, which, 

 according to Fizeau, possesses its maximum volume at that tempera- 

 ture. It will be remembered that the iodide of silver in cooling from 

 its melting point contracts like ordinary solids until it reaches a 

 temperature of 142° C, at which point it possesses its maximum 

 density, it then suddenly expands to a volume greater than that which 

 it possesses at the fusing point, and continues to expand as the 

 temperature diminishes. 



