Metals at High Temperatures. 389 



Table VII 5. 



Iron Bar. 



. 2' (mm.) ^s (mm.) 



July 19. July 21. July 25. Observed. Calculated. 



250° ) V510 j;"» I" 5 " 1-611 1-511 



315 [ 1-890 „,:, j- 1-889 2-476 2-475 



500 ) ' ' 3-459 3-459 



625 ).^„ ).„„ 0-990 4-449 (4-522) 



H* f^o till 



750 f 1 ™' P™ u 0-964 5-419 '(5'664) 



show an independent increase in length upon being magnetized, 

 which must at least be considered here. We should expect 

 with iron and steel in the weak field of the heating coil (at 

 250° 11=30, at 500°H=42 at the middle point of the bar) a 

 lengthening of the order of magnitude 5X10 -6 of the length,* 

 which for these measurements would be entirely negligible. 



The iron bar (thickness 6 mm ) was 482'7 mm long at 0° and showed 

 a permanent change after the three heatings of 0*01, —0-025 

 and — 0*025 mm respectively. 



Tables Ylla and Yllb contain the measurements, which are 

 very well represented by a parabola up to 500°. 



The equations are 



A s = 5'650* + 0'00254f (/jl) 

 A = (11705* + 5-254^} 10- 9 



Above 500° the expansion increases less rapidly. 



8. Steel 



In order that the difference in the nature of the material 

 be as large as possible, a bar of steel with a high percentage of 

 carbon was chosen. 



The original length of the bar (thickness 6 mm ) at 0° was 

 482-8 mm and decreased 0'10 mm during the first heating, but the 

 subsequent changes did not exceed 0-04 mm * 



The observations are contained in the Tables YUIa and 

 VIIB. 



If the curves 



A s = 4-428* + 0'00402* 2 ( i u) 

 A = {9173* + 8-336* 2 {10- 9 



be laid out through the points 250° and 500° the observed 

 value at 375° falls wide. The expansion of steel seems to be 

 somewhat irregular even below 500°. 



* Ewing, Induction in Iron, § 143. 



