182 



PROCEEDINGS OF THE AMERICAN ACADEMY. 



the pnmp connection with a metal piece like that shown in Fig. 6, 

 which takes the place of the lower part of the bomb. 



The construction of the auxiliary electrode is similar to that of the 

 lower one : it will be evident from Fig. 7. The jxart, a, has to be made 

 just as small as is consistent with making the joint tight on the end of 

 the crystal. The platinum covering consists of a little platinum box 

 similar to that used on the lower electrode, a short piece of tubing, b, 

 and a piece of platinum wire, c. 



The gold packing rings are made as follows : A 

 I^iece of gold wire about 3 mm. shorter than the 

 circumference of the finished ring is cut off, the ends 

 filed square and then soldered together with coin 

 gold. The wire is then annealed and placed on a 

 / Y /// /\ cast-iron spreader. By pushing a tapered brass plug 



H^^^^^^ -'^ into this spreader, it is expanded and the ring 

 ll^^t^v^— — 'j stretched. By placing a reference mark on the ta- 



pered plug, the ring can be stretched to just the same 

 size every time. It, of course, comes off perfectly 

 round, and after annealin<j is readv for use. Each 

 ring is used but once ; but after a number have been 

 used they are remelted and made into fresh wire. 



The total weight of platinum used in our bomb 

 is about 185 grams. This, together with the fine 

 construction work involved, makes the initial cost 

 considerable, but the platinum, of course, retains the 

 larger part of its value. 



Before adopting the sheet-platinum lining, at- 

 tempts were made to produce a satisfactory 2:)]atinum 

 plate on the inner surface of the bomb by the 

 electrolytic process described by Langbein * ; but 

 although a firmly adhering deposit was obtained, it was found not to be 

 dense enough to protect the surface beneath from attack and the liquid 

 from consequent contamination. 



IV. Procedure for the Conductivity Measurements. 



In making a set of conductivity determinations, the valve seat at the 

 top of tlie tube Ti (Fig. 1) is first put in order by putting in a gold 

 filling, as has already been described in Section III. Then any loose 



\7 



Figure 7. 



* Langbein's Electro-Deposition of Metals, 378 (1902). 



