220 JONES AND SCHUMB. 



a few cc. of purified mercury being added to reduce any mercuric 

 chloride present. 



Several series of cells were investigated, in the first of which metallic 

 thallium electrodes in saturated thallous chloride solution were 

 measured against the decinormal calomel electrode, at 25° and at 0°; 

 in the second series, the normal calomel electrode was used, at the 

 same temperatures. The difference in potential between the two series 

 was compared with the difference observed between the decinormal 

 and normal calomel electrodes, at the two temperatures. In the third 

 series of cells, one of the two metallic thallium electrodes was replaced 

 by a saturated thallium amalgam electrode, for the purpose of testing 

 the validity of the assumption that the two have identical potentials 

 under the same conditions. 



The measurements were made on a Wolff potentiometer of 20,000 

 ohms resistance, on the dials of which the e.m.f. could be read off 

 directly to 0.00001 v. The gah-anometer was a sensitive instrument 

 of Leeds & Northrup manufacture (type H), and the standard Weston 

 cell had been certified by the Bureau of Standards. The potentio- 

 meter was occasionally tested for parasitic and thermoelectric dis- 

 turbances. 



The filling of the calomel chamljer involved no new principles. The 

 calomel layer was at least 1 cm. liigh, and the potassium chloride solu- 

 tion was shaken up at the temperature of the experiment with a calo- 

 mel-mercury paste for about an hour previous to the filling of the cell. 

 The thallium side of the cell was filled as follows. Referring to Fig- 

 ures 3 and 4: the cock, G, (Fig. 3) was closed and L opened. The 

 pressure of nitrogen thus forced over some of the thallous chloride 

 solution from the saturation bottle into the cell; and if the vent, E, 

 cock, D, and trap, F, (Fig. 4) were opened, the licjuid would fill both 

 the lower and upper compartments, B and C, to the desired height — 

 a little below the side-arm. The cock, L, was now closed and G 

 opened, whereupon nitrogen bubbled through both the saturation 

 bottle and the cell, escaping through trap F into the air. The two 

 well-cleaned and ignited platinum electrodes, T, were now connected in 

 parallel to the negative pole of a 16-volt storage battery. The positive 

 lead was introduced into the long tube, through the bottom of which 

 was sealed the platinum anode in chamber B. The stopcock, D, 

 (Fig. 4) was adjusted so that the desired current — as registered by a 

 milliammeter — was obtained for plating out the thallium elec- 

 trodes. This plating out was continued for a shorter or longer period, 

 according to the strength of the current. Frecjuently a fraction of a 



