HALOID COMPOUNDS OF SILVER, MERCURY, LEAD, AND COPPER. H45 
eight times greater than the preceding; and (c) finally a'coefficient somewhat more 
than twice as great as that between 0° and 253° C., at temperatures above 265° C. 
Undoubtedly the iodide of lead, as in the case of the iodide of mercury, undergoes a 
molecular change, while rapidly expanding between 253° C. and 265° C., and before 
assuming the higher coefficient. This is supported by the fact that the highly brittle 
and crystalline rod showed itself capable of bending after having undergone the rapid 
expansion. It will be remembered that the iodide of silver, which is very crystalline 
and brittle below 145° C., becomes amorphous and plastic above that temperature. 
The familiar example of sulphur will also recur to the mind. 
If we suppose a mass of iodide of lead to be heated from 0° C. to the melting point 
(383° C.) the following will be the volumes at the respective temperatures :— 
Volume at 0° C.=1*000000 
„ 205 =1*015608 
„ 253 =1*019595 
„ 265 =1*027248 
„ 383 (solid).=1*048488 
„ 383 (liquid).=1*078080 
The curve is shown in Table A. 
Table A.—Table showing the relationship between the temperature and volume of 
iodide of lead, iodide of silver, and of the lead-silver iodide alloy, PbT 3 .AgT. 
7 G 2 
