M. BettendorfF on Arsenic. 455 



coating. In boiling water it disengages a small amount of hy- 

 drogen. Gently heated in the air it burns, with formation of 

 brown oxide ; but if suddenly heated more strongly, it burns with 

 explosive violence, and scatters about the most brilliant stars. 

 In this respect it differs from everything, with the exception of 

 uranium. 



BettendorfF* has described two allotropic modifications of 

 arsenic. When pure arsenic was volatilized in a rapid current of 

 hydrogen, metallic hexagonal arsenic was deposited in the imme- 

 diate neighbourhood of the heated part, and a little further on 

 there was some black amorphous arsenic, while the whole front 

 part of the tube was filled with a bright yellow fume, which as 

 it deposited became darker and finally grey. It was found on 

 analysis to be pure metallic arsenic ; it was quite amorphous, 

 and was found under the microscope to consist of small globules 

 arranged together in a chaplet-form. Its specific gravity was 

 found to be 4*71 ; and when heated from 358° to 360° it changes 

 into crystalline metallic arsenic of the specific gravity 5*72, with 

 such disengagement of heat that part of the arsenic volatilizes. 



The black amorphous arsenic with a vitreous lustre is obtained 

 when arsenic vapour is cooled to from 210° to 220°. It is best pre- 

 pared by bending one end of a combustion-tube in a U-shape, 

 and immersing this part in an oil-bath heated to 220° while the 

 arsenic, which is placed near the upper end of the tube, is volati- 

 lized in the current of hydrogen. After the experiment the in- 

 terior of the U-tube is lined with a splendid mirror, which by 

 gently tapping is obtained in a number of thin brittle scales. Its 

 specific gravity is 4*71 ; and on heating to 360° it passes into 

 crystalline arsenic, with considerable development of heat. It 

 resists chemical attack much more energetically than crystallized 

 arsenic. 



Gondolot has describedan important modification in Boussiu- 

 gault's method of preparing oxygen. Tubes either of wrought 

 or cast iron are covered on the inside with a lute of magnesia, 

 and externally with asbestos, in order to diminish the porosity 

 and the waste in the fire. These tubes are fastened in a brick 

 furnace provided with arrangements for regulating the draught 

 so that the tubes can be heated either to bright or to dull red- 

 ness. The tubes contain baryta, with which is mixed lime, and 

 a small quantity of manganate of potash, which prevents fritting. 

 Air is then passed through the tubes at a low heat, at which the 



* Liebig's Annalen, October 1867. 

 t Compies Rendus, Marcii 9, 1868. 



2H2 



