172 



Allen, Crenshaw, Johnston, and Lav sen — 



Fig. 1, 



Synthesis of iron disulphide.~-A])ip2LTa,tu$. — All the experi- 

 ments on the synthesis of pyrite and marcasite were done in 

 sealed tubes, enclosed in steel bombs and 

 heated in resistance furnaces. Several kinds 

 of glass were tried for the tubes, all of which 

 were naturally more or less attacked. The 

 Jena combustion glass and so-called " durax " 

 glass were the only kinds which were found 

 to stand satisfactorily the action of water 

 solutions at the higher temperatures (up to 

 350°), and even these are pretty rapidly 

 attacked by alkaline solutions. To prevent 

 bursting, the glass tubes were enclosed in 

 heavy steel bombs (see fig. 1), about 80 cm in 

 length by 25 mm inside and 43 mm outside diam- 

 eter, having thus a thickness of nearly a 

 centimeter. These bombs were closed at 

 one end by an iron plug, P, which was 

 welded in. The other end was threaded 

 on the outside and closed with a cap. To 

 insure a tight joint, three concentric grooves 

 about l mm deep were cut on the open end of 

 the bomb. On this was laid a copper disc, 

 E, 3 ram thick, on which was placed a steel disc, 

 _/), l cm thick. The cap was then screwed down 

 by means of a long steel lever. The steel 

 disc was used to prevent the shearing of the 

 copper disc in screwing down the cap. The 

 joint was lubricated with oil and graph- 

 ite. The glass tubes were put into the 

 bombs and water was added before closing 

 the latter, so that the pressure on the inside 

 of the glass tubes would be compensated. 

 These bombs will hold satisfactorily up to 

 temperatures of 400°. 



Furnaces. — The furnaces in which the 

 bombs were heated were electric resistance 

 furnaces, the coils of which were of nickel 

 wire O'S™ 111 in diameter, wound on a sheet- 

 iron tube 5 cm in diameter, which was first 

 wrapped with asbestos paper. The tube and 

 coil were surrounded by another sheet-iron 

 cylinder 15 cm in diameter. The space between the two was filled 

 with light magnesium oxide. Caps, also of sheet-iron, fitted 

 tightly over both ends of the outside tube, leaving at the upper 

 end (the furnaces were set in an inclined position) a space about 



Fig. 1. Bomb used 

 in heating sealed 

 tubes. 



