Properties of Platinoid and Manganine. 305 



of manganine than if they were made of the platinoid. More- 

 over this hard drawn manganine wire could advantageously be 

 used as a slide wire, since accidental heating of a portion of 

 the wire would not alter its resistance appreciably and since 

 the thermo-electric effects at the junctions of the slider would 

 be insensible. On account of its high specific resistance very 

 fine manganine wire has been much * used as slide wire in po- 

 tentiometer work. 



A pair of thermo-electric junctions made of copper wire and 

 a piece of the manganine wire no. 18 which had been kept for 

 about a minute at red heat and then suddenly cooled gave an 

 electromotive force of 65*9 microvolts when one junction was 

 kept at 23° and the other at 93°. It is instructive to compare 

 this result with the results of experiments mentioned below 

 which were made with manganine wire thoroughly annealed 

 in the manufacture. 



The numbers given in Table II for the electromotive force 

 of platinoid against copper do not agree very well with the 

 results obtained by Messrs. Bottoinley and Tanakadate who, 

 found for the electromotive force of this combination the two 

 expressions —1246 — 5*44£ and —1294 — 4*88£ in c. g. s. units. 

 My experience seems to show, that as these gentlemen sus- 

 pected, different specimens of platinoid wire have different 

 places in the thermo-electric scale. A number of thermopiles 

 made of platinoid wire no. 28 and copper gave results which 

 agreed with one another perfectly, except for such extremely 

 slight differences as might properly be charged to errors' of 

 observation, but these results were quite different from those 

 obtained with the larger platinoid wire and much closer to 

 those of Messrs. Bottomley and Tanakadate. 





Table 



ITT. 





Temperatures 



The Electromotive Force 



of the 



of 



Platinoid Wire no. 28 



Junctions. 





vs. Copper. 



0° and 



10° 





152 



0° and 



20° 





306 



0° and 



30° 





465 



0° and 



40° 





628 



0° and 



50° 





799 



0° and 



60° 





973 



0° and 



70° 





1159 



0° and 



80° 





1356 



0° and 



90° 





1569 



0° and 



100° 





1787 



* H. M. Goodwin: — Zeitschrift f. Physikalisehe Chemie, xiii, 4, 1894. 



