McELFRESH. — OCCLUDED HYDROGEN IN PALLADIU:\I. 



325 



merit. At this time, when the wire is nearly saturated, the hydrogen 

 escapes as a milky cloud of very small bubbles, many of which stream 

 around beneath the edge of the funnel and so escape to the open air. In 

 the second place, hydrogen is slightly soluble in the electrolyte, and where 

 a lar"e nuantitv of the latter is used the amount of hydrogen dissolved 

 mav be creat enoujrh to introduce a considerable error. For, by this 

 method, the computed value of the quantity of hydrogen absorbed by the 

 wire will include both that actually absorbed and also that dissolved by 

 the electrolyte. 



In order to overcome these difficulties, the final experiments employed 

 a voltameter whose capacity was only about 475 cubic centimeters, and 

 in which the palladium wire was surrounded by walls of filter paper so 

 arranged that the liberated hydrogen could not escape otherwise than into 

 the burette. 



The accompanying diagrams illustrate the construction of the appara- 

 tus. The voltameter is made by clamping quarter-inch glass plates, 



I 



7'/4'\n 



Figure 2. 



hb, in Fig. 2, to a rectangular frame, aa, of hard-rubber, a thin strip of 

 pure-gum rubber sheeting serving as packing. As thus constructed, the 

 voltameter is slightly more than one foot in depth, while its cross-section 

 measurements are shown in Fig. 2, which is one-half of actual size. 

 The increased width in the middle portion of the interior allows the 

 electrical lines of flow to be uniformly distributed around the circum- 

 ference of the palladium wire, which will thus be charged evenly from 

 all sides. The bevelled glass plates, cccc, fit loosely in narrow recesses 

 provided for them in the hard-rubber frame, aa. Their purpose is solely 

 to diminish the volume of electrolyte used. Fig. 3 — one-fourth of 

 actual size — shows the same piece of apparatus in elevation, and Fig. 4 

 shows a cross-section at a level just below that of the lower end of the 

 burette. The platinum wires, dd, parallel to the palladium wire, form 

 the positive electrode of the voltameter. In the process of charging, the 

 current, for a time, is sent in at the tops of the platinum wires and out 



