

Thermo-electric Poivers of Metals and Alloys. 105 



rising, and in some cases falling, to give assurance that the 

 temperature of the platinum wire was the same as that of the 

 junctions, and did not lag behind it. Satisfactory evidence 

 was obtained that the temperature of the platinum wire did 

 truly represent the temperature of the thermo-j unction buried 

 in the interior of the thermometer. 



We were thus enabled to obtain a series of numbers for 

 each metal, representing at defined temperatures the thermo- 

 electromotive force of that metal against lead. Having still 

 in our possession a small quantity of exceedingly pure lead 

 prepared in M. Stas's laboratory which was kindly given 

 to us by Mr. George Matthey for our previous resistance ex- 

 periments, we were enabled to measure the therm o-electro- 

 motive force of a couple formed of this pure Stas's lead and 

 the ordinary lead used by us as the associated metal for all 

 the couples. It was thus possible to reduce all our observa- 

 tions of thermo-electromotive force to a statement of the 

 electromotive force in C.Gr.S. units of a couple formed of a 

 metal M and of chemically pure lead, one junction being at 

 C C, and the other being at a platinum temperature pt as 

 defined by our standard platinum thermometer P x . In the 

 following Tables the results of all the corrected observations 

 are given, and graphically shown plotted down in the chart 

 (see Plate IV.). 



These lines of thermo-electromotive force thus found in 

 terms of platinum temperature are in all cases curved lines. 

 Wherever the curve has a maximum point so that its tangent 

 becomes parallel to the line taken as the axis of temperature, 

 the temperature at which this occurs is the neutral point of 

 that metal or alloy with regard to lead. If at any tempera- 

 ture the tangents of the curves of two metals are parallel to 

 one another, that temperature is the neutral point of those 

 two metals with regard to each other, or is the temperature of 

 inversion. 



The diagram of thermo-electric powers can be at once 

 obtained from that of the thermo-electromotive forces by 

 drawing a series of lines, the ordinates of which represent to 

 a proper scale the slope of the curves of thermo-electromotive 

 force. 



With regard to the purity of the metals employed in this 

 research, we may mention that the samples of platinum, gold, 

 silver, palladium, copper, tin, lead, cadmium, magnesium, 

 nickel (Mr. Mond's nickel deposited from nickel carbonyl), 

 zinc, and aluminium were either the same wires as were used 

 by us in- our investigation on specific resistance, or were <>f 



