HALOID COMPOUNDS OP SILVER, MERCURY, LEAD, AND COPPER. 
1153 
for every 126’53 of iodine lost 16 of oxygen is gained. No definite oxyiodide seems to 
be formed midway, but merely a mixture of CuO and Cu 3 I 3 . Cuprous iodide cannot 
be fused without some loss of iodine and oxidation of the surface. This mixture of 
iodide and oxide forms a black scum on the surface of the molten iodide, which is less 
fusible than the iodide, and which effectually protects it from the air. In casting, the 
more fluid iodide easily runs from beneath this partially oxidised surface. Some of 
the latter was fused after running off the pure iodide from beneath, and its specific 
gravity was taken, and was found, as we should expect, to be lower than that of the 
iodide; for. while the specific gravity of the latter is 5’6936, that of the partially 
oxidised surface was found to be only 5'6030. 
The iodide was found to contract considerably when it solidified. A deep hollow cone 
sinks into the mass in the act of solidifying. The change of volume which occurs in 
the passage from the solid to the liquid state was determined by the method of the 
platinum cone before described. 
Good rods of the iodide were cast by quickly fusing the powdered precipitate and 
pouring the fused iodide from beneath the semi-oxidised crust into warm glass tubes. 
The resulting cast rod was brittle and possessed a d,ark steel-grey colour, no doubt due 
to surface oxidation. The fracture was highly crystalline and the rods somewhat 
brittle. The rods were reduced by sawing to a length of 6 inches; the ends were 
rendered plane by rubbing on a level surface of sand-paper, and were furnished with 
copper caps. The expansion was determined in the apparatus described above 
(p. 1128). Unlike the iodides of lead and silver, the iodide of copper does not possess 
more than one coefficient of expansion, at least for temperatures below 300° C. 
The coefficient of cubical expansion for 1° C. was found to be 
•00007317. 
It increases but slightly with the temperature. 
If the cast rod is plunged into hot paraffine and allowed to cool very slowly the 
coefficient is somewhat lower. The determinations of the volume in the molten state 
were not satisfactory, owing to the high temperature at which the iodide fuses and 
the readiness with which it then superficially undergoes oxidation. 
The following volumes correspond to the temperatures given :— 
Volume at 0° C..=1-000000 
„ 100 .=1-007317 
200 .=1-014634 
„ 300 =1-021951 
„ 400 =1-029268 
» 500 =1-036585 
» 600 . . ‘.=1*043902 
„ 601 (solid).=1-043975 
„ 601 (liquid).=1-118401 
7 H 2 
