Section 6. Method of Procedure. 23 



and after reannealing is ready for use. Each ring is used but once; but 

 after a number have been used they are melted down 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. We have estimated that the cost of reproducing such a bomb, 

 including the labor of a machinist and all the materials except the plati- 

 num, is about 125. 



Before adopting the sheet-platinum lining, attempts were made to pro- 

 duce a satisfactory platinum 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. 



6. PROCEDURE FOR THE CONDUCTIVITY MEASUREMENTS. 



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

 top of the tube, 7\ (fig. 1), is first put in order by putting in a gold filling, 

 as has already been described in section 5. Then any loose particles of 

 graphite or dirt adhering to the flange and cover in the neighborhood of 

 the gold packing-ring are removed with absorbent cotton saturated with 

 benzene, and the screw thread on the lower part is cleaned in the same 

 manner. Both the upper and lower parts are now rinsed thoroughly with 

 good water, using the fine stream from a wash bottle to remove more 

 effectually any loose particles of graphite which may have got into the 

 bomb upon previously opening it. By this means, too, water can be forced 

 through the fine tube, 7\. If the solution to be investigated is a dilute one, 

 the rinsing must be very thorough. Finally the bomb is rinsed out with 

 some of the solution, and as much as possible of this is then shaken out. 

 The bomb is then ready for use. 



Suppose now it is desired to make a series of measurements at the tem- 

 peratures up to 281. An amount of solution which will almost, but not 

 quite, fill the bomb at this temperature is measured in from a pipette pre- 

 viously graduated to contain this amount, as will be described in section 7. 

 A gold packing-ring is annealed and cleaned by heating it in the flame of 

 a burner, and it is placed in the groove. The cover is then put in place, 

 taking care not to disturb the ring. The thread in the large nut is next 

 washed out with benzene, to get rid of any solid substance which may 

 have condensed there in a previous heating. With a piece of cloth or 



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



