Part III. 



LATER MODIFICATIONS OF THE APPARATUS AND METHOD. 



Since the work described in Part II of this publication was completed, 

 three other bombs and various heaters have been constructed and used, 

 and the experience gained in constructing these, and especially that gained 

 in adapting the apparatus to use at still higher temperatures, has led to 

 certain important modifications in the original apparatus and method, 

 which will be here described. 



21. NEW MATERIAL FOR THE SHELL OF THE BOMB. 



A hot-rolled, open-hearth, low-carbon steel has been employed in the 

 three new bombs instead of the crucible steel used in the original one. 

 This material works much easier in the lathe and thus makes the con- 

 struction of the shell easier. It is probably also better adapted to the 

 purpose, since ductility rather than extreme tensile strength is desirable. 



These bombs were all cut without forging from one bar of the steel, 

 as was also a test piece for the determination of its coefficient of heat 

 expansion. This last was determined in this laboratory by Mr. R. B. 

 Sosman by means of the Abbe-Fizeau dilatometer as improved by 

 Pulfrich.* For this purpose the specimen in the form of a ring 5 mm. 

 thick, and of 32 mm. external and 22 mm. internal diameter, was cut out 

 of the solid stock, taking care in machining it that the last cuts should 

 be very light, so as not to change the properties of the steel by the 

 mechanical treatment. Mr. Sosman found for the true coefficient of 



linear expansion (a = -r -7-) between the limits of temperature and 



/ at 



350: 



10 7 = 115 -f 0.101 t 



or for the volume of the bomb (V t ) at t : 



V t = V (l -f- 345 X 10- 7 / + 0.152 X 10- 7 1 2 ) 



22. SCREW-THREAD ON THE STEEL SHELL. 



The ordinary thread of the form > originally used has been replaced 



by a thread of the form ^, as is illustrated in fig. 9. This form of thread 

 reduces friction, prevents the spreading of the large nut with use, which 

 was noticeable with the ordinary thread and which, of course, weakened 

 the bomb, and prevents the slight lifting of the cover which took place, 



*Z. Instrumentenkunde, 13, 365, 401, 437 (1893). 



59 



