Art. XVI. — Physical GonHtanU of Thallium. 



(With Plate XVII.) 



By W. HuEY Steele, M.A. 



[Read November 10, 1892.] 



Being in possession of a piece of thallium, and being 

 unable to find its constants in the ordinary books of reference, 

 [ determined a few of tliem as follows. The investigation 

 was conducted in the Physical Laboratory of the Universit}^ 

 of Melbourne. 



(1) Coefficient of Expansion. 



A piece of the thallium was drawn into a wire about 

 foui'teen inches long, the ends cut off square, and a nick 

 made near each end. It was put into a glass tube through 

 which steam could be passed at will from a small boiler. 

 The ends of the tube being firmly clamped, micrometer 

 microscopes were focussed on the ends of the wire. These 

 instruments, supplied by the Cambridge Scientific Instru- 

 ment Co., read to xo^oo ^^^^^^- I'l^e positions of the ends of 

 the wire and of the outer and inner edges of each nick were 

 observed, the observations being repeated several times. 

 The temperature of the thallium was assumed to be that 

 indicated by a thermometer left lying beside the glass tube 

 all night, 16-8° C. Steam was then passed along the tube 

 till it was fairly dry, and after about fifteen minutes, the 

 observations of the positions of the nicks and ends of the 

 wire were repeated, the temperature being assumed to be 

 1 00° C. The gain in length of the whole wire was observed 

 to be •02()1 inch, between the outer edges of the nicks 

 •()25o inch, and between inner edges •0255 inch. On re- 

 placing the glass tube by a scale, the length of the wire was 

 found to be 13"83 inch, and the distance between the nicks 

 13'69 inch. Dividing the increase in length by the rise in 

 temperature (83-2°), and by the length measured, the co- 

 efficients come out 0000227, -0000224, 0000224, giving as 

 mean result -0000225. 



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