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XLV. On the Thermo-electric Tension of Minerals. 

 By Walter Flight, D.Sc* 



PROFESSOR BUNSENf has already called attention to the 

 strongly electro-negative properties of copper pyrites and 

 pyrolusite, with respect to copper or an alloy of antimony and 

 zinc, and to the consequent value of these minerals for the con- 

 struction of a sensitive thermo-electric pile. In order to com- 

 plete these investigations, experiments were made with all pro- 

 curable minerals which conduct electricity, for the purpose of 

 ascertaining how they comport themselves in this respect. 



For this purpose the following apparatus was used :— Two 

 square pieces of thick platinum-foil, m and n, 10 millims. in 

 length, were firmly nailed with sprigs made of platinum wire to 

 the board A, leaving a groove between them 1 millim. in width. 



Each of these plates pressed tightly against a platinum wire, the 

 other ends of which communicated with their respective binding- 

 screws. To the binding-screws were fastened the wires of the 

 galvanometer. 



A piece of firebrick was sawn into the shape B, 21 millims. 

 w 7 ide and about 120 millims. long. Hound its narrow end (p) 

 was bound a strip of platinum-foil 10 millims. in width. 



To test any given mineral by means of this apparatus, apiece 

 about the size of a small pea, thoroughly cleaned, was placed on 

 the platinum plate n, which we will call the test-plate, and a 

 piece of antimony of the same size on the other plate m. The 

 firebrick holder was then taken in the hand, and its platinum end 

 p heated in the Bunsen flame ; it was then rested on the two sub- 



* Communicated by the Author, 

 f Poggendorff's Annalen, vol. cxxiii. p. 505 (1864). 

 Phil. Mag. S. 4. Vol. 30. No. 204. Nov. 1865. Z 



