20 Conductivity of Aqueous Solutions. Part II. 



If, after the bomb has been in use for some time, it is necessary to 

 remove the lower electrode, it may be done in the following way : The nut 

 A r can not be unscrewed, but enough of it can be removed with saw and 

 file so that the remainder will slip through the hole in the brass washer. 

 A light direct blow with the hammer on the end of the electrode rod is 

 then always sufficient to start it out. The brass remaining in the threads 

 of the electrode rod is easily removed with any pointed tool, and the elec- 

 trode is ready to use again. 



The cover B is made slightly concave to allow the air bubbles, which 

 might otherwise collect under it, to escape into the electrode chamber 

 above. To line the cover a round disk of platinum-iridium alloy contain- 

 ing 15 per cent iridium is taken, and the two tubes, T 1 and T 2 , are soldered 

 to this with pure gold. This alloy is used rather than pure platinum on 

 account of its greater hardness, which prevents the gold ring from cutting 

 into it. 



In the development of the bomb, the tube T 2 has probably caused more 

 trouble than any other part. This is due in part to the fact that at high 

 temperatures the pressure is sufficient to force water through the lining at 

 any unsupported spot. If the tube was made of heavy metal, and especially 

 when it was made of the 2 per cent alloy, it was itself capable, owing to 

 its small diameter, of withstanding the pressure without expanding enough 

 to come into perfect contact with the steel at all points ; as a result, the 

 bomb would leak at such points. Or, owing to the greater difficulty in 

 mechanically expanding the small tube to meet the shell, the fit would be 

 so poor at the start that the hydraulic pressure would tear it. Our earlier 

 work here was done with the 2 per cent alloy before we fully realized the 

 great difference in ductility between this and pure platinum. Because of 

 its extreme ductility gold was then tried. This worked beautifully at first. 

 but finally failed because the 22-carat gold solder employed in making the 

 tube disintegrated under the action of the hot water. Recourse was then 

 had to pure platinum, which completely solved the difficulty. The plati- 

 num tube is first expanded by driving in some plugs of cotton with the help 

 of a hammer and a brass rod almost as large as the inside of the tube. 

 Seamless tubing might be advantageously used here, but we used a tube 

 made of sheet platinum soldered with pure gold, and this proved to be 

 entirely satisfactory. 



The small tube T 1 is conveniently made by rolling up tightly some thin 

 sheet platinum and then flowing gold in to fill the spaces between the con- 

 volutions. This gold is fed in from the outside, while the whole tube is 

 kept hot in a large blast-lamp flame. Care must be taken not to use too 

 much gold ; otherwise a drop may form inside the tube, and its removal by 



