328 



PROCEEDINGS OF THE AMERICAN ACADEMY. 



is very carefully protected from the electrolyte by means of a special 

 acid-proof cement which covers the submerged portion of the copper wire 



and the soldered end of the palladium. 

 The two branches ^of the copper wire are 

 further protected by soft-rubber tubing 

 ("pure-gum"), which forms a water-tight 

 jacket, its lower ends being closed with 

 cement. To the lower end of the palla- 

 dium wire are soldered two long copper 

 wires which lead to outside connections. 

 Incasing one of these wires in a rubber tube 

 of very small bore serves to insulate them 

 from each other ; a rubber tube of larger 

 bore contains the pair of wires, thus insulated 

 from one another, and protects them from contact with the water in the 

 outer jar. The palladium wire increases in length as it absorbs hydrogen, 

 and must be subjected to a considerable tension if it is to be kept straight. 

 To this end a glass tube, about two inches long, is drawn over the lower 

 lead-wires until it encloses the lower end of the palladium; the upper end 

 of this tube is filled with cement ; and over its lower end is drawn the 

 larger rubber tube mentioned above. In this way a water-tight jacket is 

 provided for the lead-wires, from the soldered junction to the outside 

 connections, and no metal, excepting the platinum and palladium elec- 

 trodes, is anywhere exposed to the electrolyte. The glass tube passes 

 through a hole in the bottom of the hard-rubber frame, and a soft-rubber 

 washer cemented to the latter allows freedom of motion to the tube and 

 at the same time prevents escape of electrolyte. This washer is shown 

 as r in Fig. 3. A heavy iron weight, I, is attached to the rubber-incased 

 lead-wires, and serves to keep the palladium wire straight as its length 

 increases under the charging process. 



In order that the electrolyte may easily be kept at a constant level in 

 the voltameter, a branch tube in the side of the burette, near its lower 

 end, leads outward, and finally dips into a larger jar of the electrolyte 

 placed near the voltameter. This jar is shown on a small scale in Fig. 3. 

 When the burette is filled with electrolyte this branch tube also fills, 

 and thereafter the level of the electrolyte in the voltameter may be 

 adjusted by raising or lowering this outer vessel. 



The voltameter, with the iron weight hanging below it, is suspended 

 in a glass jar of about 40 liters' capacity, filled with water. This water 

 bath serves to prevent sudden changes of temperature, while a mechanical 



