Section 5. Construction of the Bomb. 75 



a leak in case one exists, for when the bomb is connected to the hydraulic 

 pump to be tested, as will be explained later, they permit the water to 

 escape at a point near where it gets through the platinum lining. To fur- 

 ther this end a small hole is also drilled from the outside obliquely into 

 the air space around each of the electrode rods. 



The lining of the lower part of the bomb A was made of a platinum- 

 iridium alloy (2 per cent iridium) 0.40 mm. thick. The flange F was orig- 

 inally made of the same material, but the closing of the bomb compressed 

 the platinum each time under the ring so that it grew hard and thin and 

 finally cracked at the bottom of the groove. For this reason platinum- 

 iridium alloy containing 15 per cent iridium had to be substituted for the 

 flange. This is so hard that it bids fair to wear indefinitely, and yet it is 

 not so brittle that it can not be forced into the groove in the steel without 

 cracking. The flange could just as well be welded to the platinum cup, 

 but in our bomb it was soldered to it with pure gold. Pure gold was also 

 used freely in making repairs on the present lining when it tore, as it fre- 

 quently did at the start, before the necessity of the small holes in the shell 

 and of several other precautions was understood. 



The lining is made so as to fit as well as possible at the start. It is then 

 inserted in the shell, and expanded by driving in plugs of cotton as hard as 

 possible, with a hammer and piece of hard wood. The shell is then placed 

 in the lathe, and the lining is still further expanded by the use of an agate 

 burnisher lubricated with soap. The flange is next hammered over to fit 

 the steel, sheet lead being used under the hammer to prevent injury to the 

 platinum alloy. The most delicate operation connected with the lining 

 of the bomb is perhaps the next step, which consists in making a depres- 

 sion in the flange to fit the V-shaped groove in the steel below. This 

 groove in the steel should not be sharp as shown in fig. 1, but should be 

 slightly rounded at the bottom (to prevent cracking the hard flange) and 

 its sides should make an angle of 90 with one another. The depth of the 

 groove is such that when a wire 0.8 mm. in diameter is laid in it, about 

 one-half of the wire lies outside the groove. A little steel roller is made 

 to fit the groove in the shell, and this roller, after being hardened and 

 polished, is pivoted in a fork which fits into the tool post of the lathe. 

 The shell with the lining in it is then slowly rotated in the lathe while the 

 roller, well lubricated with soap, is firmly pressed against the flange over 

 the groove. 



After the lining has been made to fit as closely as possible, it should 

 be removed from the shell and heated to redness to anneal it. Even the 

 flange had better be treated in this way, since it is hard enough even after 

 annealing. To remove the lining after it has been fitted in in the preceding 

 manner, the following plan was adopted : Take a stick of soft wood, per- 



