14 Conductivity of Aqueous Solutions. Part II. 



shell was designed for approximately equal strength throughout. The 

 large nut C has an ordinary V-shaped thread of 18 turns to the inch. 

 To tighten the nut, the lower part of the bomb is held at R, which is hex- 

 agonal, by a wrench bolted to a firm table ; while a second wrench, with 

 an effective length of 46 cm., is placed on the hexagonal part R' of the nut 

 itself. In this way sufficient pressure can be exerted on the gold packing- 

 ring to make the metal of which it is composed actually flow into the 

 groove beneath, filling any little scratches or other depressions which may 

 exist in the latter. Since there is a certain thickness of gold and platinum 

 interposed between the cover and the lower part of the bomb, and since 

 these both expand less than steel upon heating, it becomes necessary to use 

 a compensating brass washer W between the nut and the cover. The 

 proper thickness can be calculated from the known coefficients of expan- 

 sion of the three metals. Care must be taken that the bearing surface of 

 the nut C on the washer W is so large that the upward force of the 

 steam acting on the cover does not compress the brass washer, and thus 

 allow the cover to rise. Care must also be taken and this is very 

 important that the distance from the center of this bearing surface to the 

 axis of the bomb is less than the radius of the gold packing-ring; other- 

 wise the cover might turn on the ring while the nut was being tightened, 

 which would prevent a tight joint from being secured. For lubrication 

 a little finely powdered graphite is rubbed on the top of the brass washer 

 and into the threads of the large nut. 



To facilitate the removal of the platinum lining, the inside of the steel 

 shell was made slightly tapering (about 0.05 mm. in 10 cm.), and the little 

 grooves left by the boring tool were carefully ground out. 



In working with the bomb it proved to be necessary to drill through the 

 steel shell a number of small holes, one of which is shown at H in fig. 1. 

 In the present bomb there are about 75 of these (probably half as many 

 would have sufficed) well distributed over all its parts, A, B, and C. These 

 holes are 0.66 mm. in diameter so small that they do not seriously 

 weaken the shell, and that the platinum lining is capable of withstanding 

 the pressure over their areas. These holes are made necessary by the 

 fact that without them some water gets trapped between the lining and 

 the shell, owing to slight leakage or permeation of the platinum itself when 

 the bomb is first heated, the lining then being not in close contact with the 

 shell at every point; and this water on subsequent heating exerts, owing 

 to its expansion in the liquid state, an enormous pressure against the lin- 

 ing, causing little indentations in it and causing some water to flow back 

 into the bomb, whereby contamination of the solution with iron is pro- 

 duced. The holes remedy entirely this difficulty, which otherwise will 

 become aggravated on each successive heating. They also help to locate 



