Sections 24 and 25. Modifications of the Apparatus. 61 



pari; of platinum and in part of gold. This plan is illustrated in fig. 11. 

 a, a is the flange, which is now made of a platinum-iridium alloy con- 

 taining 12 per cent of iridium ; for this alloy is sufficiently hard for the 

 purpose and can be rolled into the groove in the shell without the slight 

 danger of cracking inherent in the use of the 15 per cent alloy, b, b is 

 the body of the lining and is made of commercially pure platinum, which 

 has the advantage of being somewhat more ductile than the ordinary 

 platinum containing about 2 per cent of iridium, c, c is a cup of fine gold, 

 formed by pressing a sheet of gold through a die. It is about 1 cm. high 

 and is fused at its upper edge only to b, b. Its advantages over platinum 

 are that it is more ductile and therefore easier to fit in place ; that it prob- 

 ably does not offer so easy a passage through its pores to water at high 

 temperature ; and that its expansion-coefficient is nearly equal to that of 



steel, thus diminishing the difference in expansion of the 

 "I f^- lining and shell, d is a circular disk of platinum-iridium 



alloy with 15 per cent iridium, about 1.3 cm. in diameter. 



The use of some such hard and smooth material is imper- 

 b ative at this point, since otherwise the lining would 



become indented under the V-shaped ridge on the end of 



the quartz insulator, and it would then be very difficult, 



after the first time, to put in an electrode so that it would 

 d" be tight. 



Fig. 1 1 The flange is still, as it was originally, soldered with 



fine gold to the body of the lining. The upper end of the 

 gold cup is very easily fused to the platinum by bringing the flame of the 

 blast lamp onto the outside of the platinum a little above the level of the 

 cup. Before fastening the cup in place it is well to put in the platinum 

 piece, d. For this purpose the gold cup is inverted, and the disk, which is 

 about 2 mm. larger than the hole in the cup, is placed over it. The flame is 

 then brought onto the platinum. 



The thickness of the different pieces of sheet metal used in the lining 

 is, as originally, 0.41 mm. 



25. A METHOD FOR REMOVING THE LINING BY HYDRAULIC PRESSURE. 



The original method for removing the lining, described in Part II, 

 section 5, was applicable only in case the bomb had not been previously 

 heated. In case it had been heated, no method was available for removing 

 the lining without spoiling the flange and seriously straining the metal 

 composing the body of the lining. But by utilizing the chuck described in 

 section 23 the lining can at any time be readily removed without injury by 

 a method to be now described. The same method would also be applicable 

 to the removal of the lining from calorimetric bombs, or even to the 



