296 Mr. G. F. Rodwell on the Effects of Heat 



In the expansion-apparatus the bar expanded as regularly but not 

 quite so rapidly as the alloy No. 1. Up to 124° C. the coefficient of ex- 

 pansion is nearly the same as that of the bromide of silver. Between 

 124° C. and 133° C. it contracted more than the preceding ; at 133° C. 

 the rod began to expand again, and it expanded now both more than the 

 bromide and more than alloy No. 1 during the same ranges of tempera- 

 ture. At the melting-point the volume is less than that of the bromide, 

 however, and at 750° C. it is nearly the same. 



The following results were obtained : — 



Coefficient of cubical expansion for 1° C. 



° 0. ° 0. 



Between and 100 = -00009529 



100 and 124 = -00010451 



„ 124 and 133 (contraction) = -00060000 



133 and fusing-point (295° C.) = -00020250 



Expansion in passing from the sohd to the liquid state = -05084000 

 Between 295° 0. and 750° = -00016130 



It is curious and anomalous that the coefficient of expansion of the 

 liquid between 295° C. and 750° C. should be less than that of the solid 

 between 133° C. and 295° C. ; but the results were concordant, and it 

 must be noted that the expansion between 133° C. and 295° C. is nearly 

 double that of the most expansible of metals. The coefficient between 

 these limits appeared to decrease as the temperature rose ; but as the mass, 

 or at least one of its constituents, undergoes at 133° C. a molecular 

 change, passing into an amorphous plastic condition, and as of necessity 

 there is some strain on the rod, it was thought that this decrease of the 

 coefficient might be due to increase of plasticity and consequent slight 

 yielding of the bar ; and the first determination (that is to say at the 

 lowest temperature possible above 133° C.) was taken, and the above 

 coefficient, which may consequently be somewhat too high, was deduced 

 from it. 



If we take the volume at 0° C. as unity we have — 



Yolume at = 1-000000 

 100 = 1-009529 

 124 = 0-012037 

 133 = 1-006637 

 295 = 1-039442 (solid) 

 295 = 1-090280 (liquid) 

 750 = 1-163720 



The alloy has two points of similar density at difEerent temperatures, 

 owing to the contraction which takes place between 124° and 133° C. 

 The one temperature is 133° C, the other at or about 70° C. 



