Disintegration of Platinum and Palladium Wires. 481 



there is a second good clenvage parallel to the possible faces 

 which have been selected as the form {110}. 



The fracture is conchoidal. The specific gravity of the 

 crystal was determined by suspending it in methylene iodide, 

 and has the value 3*185 at 22° C. The hardness is about 

 that of felspar. The lustre is vitreous, but pearly on b. The 

 plane of the optic axes is 1 0, the acute bisectrix is perpen- 

 dicular to 1, and the crystal is optically positive. 



By refraction through a prism bounded by two of the faces 

 of the form v it was possible to obtain the value of the index 

 of refraction, 7 = 1-622 (sodium light), of a ray vibrating 

 parallel to the acute bisectrix. By immersing the crystal in 

 a liquid of about the same refractive index as itself, an 

 approximate value for the angle between the optic axes was 

 obtained, 2V=69^°. 



Chemical examination of a portion of the crystal has shown 

 it to be a hydra ted silicate of sodium and calcium containing 

 about 6 per cent, of oxide of tin, which seems to replace an 

 equivalent quantity of silica. 



Before the blowpipe the substance loses water, but remains 

 infusible ; it is not dissolved by concentrated hydrochloric acid. 



LIII. On the Disintegration of Platinum and Palladium 

 Wires at High Temperatures. By Walter Stewart, 

 M.A., D.Sc, late 1851 Exhibition Science Scholar, University 

 of Glasgow*. 



ACCORDING to Aitken'sf investigations, air which has 

 been freed from dust has partially lost the power of 

 forming clouds in the presence of water vapour. Prof. 0. 

 Lodge"): found that the power is recovered after a platinum 

 wire has been brought to a " glowing " temperature by an 

 electric current in the dust-free air. From this it has been 

 concluded that solid particles are projected from the wire, or 

 that the wire surfers disintegration ; and under suitable con- 

 ditions a dark-coloured deposit is seen on the walls of the 

 vessel containing the air after the glowing. Elster and 

 Geitel § observed that in an atmosphere of hydrogen a glow- 

 ing platinum wire does not disintegrate. This was confirmed 

 by Nahrwold ||, who determined also by direct weighing the 

 amount of the disintegration of the glowing wire in air. 

 Nahrwold concluded that the disintegration, if not determined, 



* Communicated by Lord Kelvin. 



t Aitken, "On Dust, Fog, and Clouds," Trans. R.S.E. 1883; Proc. 

 PS E. 1881, vol. xi. pp. 14, 122; ' Nature,' 1883. 



X Pro!" O. Lodge, ' Nature,' vol. xxxi. p. 268 (1885). 



§ Elster and Geitel, Wied. Ann. xxxi. p. 126 (1887). 



|| R. Nahrwold, Wied. Ann. xxxi. p. 467 (1887) ; xxxv. p. 116 (1* 



Phil. Mag. S. 5. Vol. 48. No. 294. Hov. 1899 . 2 L 



