Intelligence and Miscellaneous Articles. 547 



to 208°. The only difference which exists between these two bodies 

 is, that with sulphur the ordinary temperature is sufficiently near 

 that at which the change of state takes place for the transformation 

 to be gradually effected ; whilst in tlie case of selenium, it is requi- 

 site to raise it to a more elevated temperature in order to cause it 

 to pass from the amorphous iuto the crystalline state. 



In many chemical reactions the selenium is separated from its 

 solutions in the form of an amorphous red powder. It is obtained 

 thus by precipitating selenious acid by sulphurous acid, by the 

 chlorides of tin, zinc, iron, or by exposing a solution of hydroselenic 

 acid to the atmosphere, or by diluting with water a solution of 

 amorphous or crystallized selenium in concentrated sulphuric acid. 

 These precipitates have only to be exposed to the action of the 

 solar rays to make them gradually pass into the crystalline state. 



In other circumstances selenium may be precipitated at the ordi- 

 nary temperature in the crystalline state; for instance, when solu- 

 tions of seleniuret of potassium or ammonium are exposed to the air. 



Selenium exhibits very different densities in its two allotiopie 

 modifications. In its amorphous state the specific gravity is 4'26- 

 4 - 28, whilst in the crystalline it is 4"80 ; its conductibiiity for elec- 

 tricity likewise varies considerably; the vitreous selenium insulates 

 almost perfectly, whilst the crystalline substance is a very excellent 

 conductor. In this state it exhibits a very curious phenomenon, 

 that of the resistance decreasing in proportion as the temperature 

 rises, provided its point of fusion be not attained. 



The author concludes his memoir by some observations on the 

 analogy which exists between the phenomena of allotropy presented 

 by sulphur and selenium and that which M. Sohrcetter has published 

 regarding phosphorus; he thinks that the latter chemist commits a 

 mistake in considering the red phosphorus as amorphous ; and 

 although we have not yet been able to obtain this modification in 

 the crystalline state, he believes that it is the state of pho-phorus 

 corresponding to the crystalline sulphur and selenium, and that very 

 probably this body, in passing into that state, likewise disengages a 

 quantity of heat. — Poggendorff's Annalen, lxxxiv. p. '211. 



METEOROLOGICAL OBSERVATION. BY P. J. MARTIN. 



The perpendicular column of light seen in the horizon at sunset 

 in April, as described by your Orkney correspondent, was also seen 

 in this part of Sussex. I did not get sight of it more than once; 

 because, supposing it to be of a transient and local character, I did not 

 look for it again. Here it was singularly vivid, and faded gradually 

 away, or rather followed the sun, as described by your friend and 

 the correspondents of the Times. It had none of the character of 

 the zodiacal light, but rather looked like the columnar prolongation 

 of the sun described by oriental travellers as frequent in the east ; 

 and it immediately suggested to my mind (as it seems to have done 

 to some of the above-mentioned observers) the columnar light in 

 Martin's " Exodus," the " pillar of fire " moving before the Israeli- 

 tish host. 



Pulborough, June 4, 1852. 



2 N 2 



