160 Barker — Tliermoelectromotive Forces of Potassium 



means of a Sprengel pump, and drew in melted sodium from 

 a bath of paraffin." 



Naccari and JBellati* measured the tliermoelectromotive 

 forces of sodium-copper and potassium-copper couples, and, in 

 order to refer to lead, of a lead-copper couple. The circuit 

 was simply completed through a galvanometer of high sensi- 

 bility, and the deflection noted. Then, the resistance of the 

 couple and of the galvanometer being determined, and the 

 galvanometer calibrated by a Daniell cell of known electro- 

 motive force and resistance, the tliermoelectromotive force was 

 calculated. The metals were melted under petroleum of high 

 boiling point in wide vertical tubes, and narrower tubes filled 

 by simply inserting, with the upper end closed with the finger, 

 and then removing the finger and thus allowing the pressure 

 of the petroleum in the large tube to force the molten metal 

 up into the narrow tube. When the metal had cooled and 

 solidified, the tube was withdrawn and the ends of the copper 

 wires, which were threaded, forced into the solid metal. The 

 sodium tube was straight ; the potassium tube, in order that 

 measurements might be made with one junction at a tempera- 

 ture above the melting point, was terminated by a U. The 

 junctions were surrounded and protected by petroleum, con- 

 tained in glass globes provided with the necessary tubulures. 

 Heat was applied by means of a water-bath. 



I have not had access to the original communication, and 

 have had to depend on an abstract in the Journal de Physique,. 

 1877, which, while quite full in many respects, gives but few 

 numerical results, stating only the values found for the "spe- 

 cific heat of electricity" and the temperatures of the neutral 

 points. 



This is the most recent investigation of the thermoelectric 

 properties of potassium and sodium of which I have found a 

 record. 



The present communication deals with the measurement of 

 the thermoelectromotive forces of potassium platinum and 

 sodium-platinum couples for varying temperature-differences 

 between 0° and about 90°, and, for the purpose of comparison,, 

 of a mercury-platinum couple through the same range, by a 

 potentiometer method. There was available for this use a 

 Leeds potentiometer, adjusted to read directly in volts when 

 used in connection with a Weston standard cell of 1*0193 volts. 

 The potentiometer was carefully tested and some corrections 

 made. The certified electromotive force of the cell was veri- 

 fied by a comparison made by the National Bureau of 

 Standards. 



The galvanometer used was a high sensibility D' Arson val 



*Nuovo Cimento, xvi, pp. 120-130, 1876. 



