Intelligence and Miscellaneous Articles. 237 



resistance of a cylindrical wire is expressed thus, C= pw» where L 



is the length, P the weight, R the resistance, and D the density of 

 the wire. 



Determination of the Density. — The density of thallium, as referred 

 to water, cannot be directly obtained, for it dissolves to an extent 

 which cannot be neglected ; 5 grammes lose during the operation 

 10 milligrammes. Naphtha was used which had stood over sodium, 

 and the following densities refer to naphtha at a temperature of 1 1° : — 



\ (Y\ 14-S51 1 Mean. 

 Thallium in plate prepared by M. Lamy I ^* 14-342 f *4*346. 



Thallium melted | ^] u-Hg } 1*330, 



Thallium in wire 1 millim. in diameter. . < L\ 14-992 f 14'276.- 



From these results it appears that the mechanical action of the 

 hammer and of the draw plate produce a slight diminution of density 

 of about yuVo-* The density of the naphtha having been found to be 

 0-8275, the density of melted thallium at 11° is 11'853, — a value 

 which well agrees with M. Lamy's numbers, 11*862 at 0°, the den- 

 sity of the same metal in the form of wire being 11*808. 



Determination of the Conductivity. — Four different wires were 

 experimented upon ; the ends of the wires were held in copper 

 clamps, and the wire was immersed in a vessel filled with naphtha. 



Length of 



the wire, 



L. 



mm. 



311 



Weight, 

 P. 



Dig. 



1773 



Resistance, 

 R. 



120-0 



Value of i 

 r L 2 D 

 C= PR- 

 5-36 



Tempc 

 ture 



o 



15 



190 



1255 



64-6 



5-38 



10 



260 



1182 



129-6 



5-21 



11 



190 



504 



161-4 



5*24 



12 







Mean 



. 5*30 



12 



The resistance was always determined a short time after the wire 

 had been drawn ; but its surface was nevertheless covered with a layer 

 of oxide ; yet, as it was not possible to observe an increase of resist- 

 ance from this time, it is presumable that the influence of this cir- 

 cumstance on the conductivity may be neglected. A wire exposed 

 to the air for twenty-four hours experienced an increase of resistance 

 of about y^. The mean of the values of C is 5-3 at the tempera- 

 ture of 12° compared with mercury at 14°. The conductivity of 

 mercury is 1*63, that of silver being 100, which gives for thallium 

 8-64, a value between that of lead 7*77, and that of tin 11*45, and 

 which is far less than the conductivity of the alkaline metals. 



Variation of the Resistance with the Temperature. — The resistance of 

 the same wire was determined at three different temperatures : — 



