1136 
MR. G. F. RODWELL ON THE EFFECTS OF HEAT ON CERTAIN 
that the iodide possesses its maximum of volume or minimum of density at a tempera¬ 
ture of -60° C. (-76° F.). 
M. Fizeau’s determination was adopted for the range of temperature between 
— 10° C. and +70° C. 
For higher temperatures the iodide was examined in the expansion apparatus 
(p. 1128). Careful castings were made of the iodide in tubes of thin warm glass, 9 inches 
long by 0'3 inch diameter. The ends were sawn plane and carefully worked on fine 
sand-paper so as to produce a rod 6 inches in length. Copper caps were fitted on the 
ends of the bar, and it was supported in the cradle G (fig. 4) of the apparatus. By 
turning the micrometer-screw the index was forced up to 135° of arc. Water was 
used for heating the bars up to 90° C., and ceresine for higher temperatures. On 
heating the bar the index began to retreat very slowly, showing contraction, and this 
continued until a temperature of 142° C. was attained, when the contraction became 
more rapid; between 148° C. and 151°*3 C. it was very rapid, at 156°'5 C. it ceased 
altogether, and the needle was motionless, showing that although heat was being 
absorbed neither contraction nor expansion was taking place; and at 163° C. expansion 
commenced and continued to the melting point. 
The contraction, as stated, commenced at 142° C. and terminated at 156 0, 5 C.; but it 
mainly took place between 148° C. and 151 0, 3 C. Thus in all for the 14 0, 5 C., during 
which the mass contracted, the index retreated through 18 revolutions of 135° to 0° 
of arc of the instrument, and these were related to the temperatures in the following 
manner:— 
1 revolution of the index took place during heating from 142° to 148° 0. 
14 „ „ „ 148° „ 151°-3 C. 
2 „ „ „ 151°-3 „ 153° 0. 
1 „ „ „ 153° „ 156°-5 C. 
Coefficients of cubical contraction and expansion for 1° C. 
Between. 
0° 
and 70° C. 
= -•00000417 
>> 
70° 
yy 
142° C. 
= -•00001749 
5? 
142° 
yy 
148° C. 
= -•00016363 
» 
i—* 
00 
o 
yy 
151°-3 0. 
= -•00420000 
yy 
151°’3 
yy 
158° O. 
= -•00120000 
yy 
153° 
yy 
156°-5 0. 
= -•00030000 
yy 
156°-5 
yy 
163° 0. 
= -00000000 
yy 
163° 
yy 
527° C. 
= + •00006921 
Plus has been placed before the coefficient of expansion on heating, minus before 
the coefficients of contraction. The increase of volume in passing from the solid to 
the liquid state was determined by the method described on p. 1132. 
If we take the volume at 0° C. as unity, the following volumes correspond to the 
temperatures given between 0° and the melting point:— 
