544 



Mr. G. F. Rodwell. 



for eight minutes, during which the cover was three times 

 momentarily removed. Violet fumes of iodine escaped on each 

 occasion, but on weighing the loss was found to amount to only 



•11036 per cent. 



Again, the mass was kept fused for four minutes, and the crucible 

 cover was twice removed, but the loss had only increased to 



•1584 per cent. 



After a third fusion the total loss only amounted to 



'1718 per cent. 



Hence it is manifest that iodide of lead may safely be fused out of 

 contact with air, with scarcely appreciable loss. When, however, the 

 crucible cover was permanently removed, the iodide rapidly decom- 

 posed. 



When the iodide was heated in a current of carbonic anhydride y 

 it sublimed unchanged in crystals ; while if it was heated in a 

 current of dry oxygen it rapidly decomposed, fine crystals of iodine 

 collecting in the fore part of the tube. 



The specific gravity of iodide of lead, in common with the iodides 

 of copper, silver, and potassium, is less than the mean specific gravity 

 of its constituents. Karsten found it to be 6'0282, Boullay 6*11, and 

 my own determinations gave 6'12. The calculated specific gravity is 

 6-629. 



The fusing point as determined by Mr. Carnelley is 383° C. 

 The coefficient of cubical expansion for 1° 0. was found to be 



•00007614 



for temperatures between 0° 0. and 205° 0. It increased to 



•00008317 



between 205° 0. and 253° C. 



Between 253° C. and 265° C. the mass expanded rapidly, with a co- 

 efficient nearly eight times greater than the previous, viz. : — 



•0006378. 



After the subsidence of this rapid expansion it no longer retained the 

 original coefficient, but assumed one of more than double the amount,, 

 viz. : — 



•000180. 



At temperatures some distance from the melting point the rod began 

 to bend, and it became necessary to assume that this last coefficient 

 continues to the melting point. The expansion in passing from the- 

 solid to the liquid condition was determined by the method described 

 in my previous paper. 



