Mineral Sulphides of Iron. 173 



6 cm long for the head of the bomb. A hole about 6 ram in diam- 

 eter through the lower cap admitted the thermo-element. The 

 variation in temperature along the outer wall of the bomb, from 

 a point about 5 cm from the lower end to another 20 cm farther 

 up, was only about 5°, which is within the error of the direct- 

 reading galvanometer used. This instrument was calibrated 

 within that degree of accuracy, but as none of the tempera- 

 tures involved had reference to any critical point, it was not 

 considered worth while to measure more accurately. 



The action of hydrogen sulphide on ferric salts.— The first 

 action of hydrogen sulphide on ferric salts is, of course, the 

 immediate reduction of the latter and the simultaneous precip- 

 itation of sulphur : Fe 2 (S0 4 ) 3 + H 2 S = 2FeS0 4 + H 2 S0 4 + S. 

 No further action has hitherto been noticed, but in a closed 

 vessel where the hydrogen sulphide is prevented from oxida- 

 tion or escape, a second reaction proceeds, viz : FeS0 4 + S -f- 

 H 2 S = FeS a + H 2 S0 4 . At room temperatures, the velocity 

 of this change is very slow, but at 200° it is relatively rapid. 

 The following data prove beyond question the nature of this 

 latter reaction : 



3 g. FeS0 4 .7H 2 with 0*17 g. H 2 S0 4 , 0*75 g. sulphur and 

 100 cc water saturated at 0° with H 2 S, were sealed up in a glass 

 tube and heated about 2 days at 200°. The product was 

 purified by washing first with water, then digesting with 

 ammonium sulphide to remove excess of sulphur, washing again 

 with water, boiling out with 20 per cent hydrochloric acid, 

 and finally washing in an atmosphere of carbon dioxide and 

 drying in vacuo. 



Analysis: Product taken, 0-5044 g. Fe 2 3 found, 0*3346 g. 



Found Cal. for FeS 2 



Fe._ 46*44$ 46*56$ 



Another product was formed by heating at 100° for six days 

 the following system : 5 g. FeS0 4 .7H 2 0, 0*5 g. S, 0*17 g. H 2 S0 4 , 

 and 100 cc water saturated at 0° with H 2 S. The product was 

 purified in a way similar to the above. 



Analvsis: Product taken, 0*5003 g. BaS0 4 found, 1*9598 g. 

 " " 0*5006 g. Fe 2 3 " 0*3295 g. 



Found CaL for FeS 2 



Fe _ 46*06$ 46*56$ 



S 53*81 53*44 



•87 100*00 



Both these products were similar to natural marcasite in color 

 and luster. Their crystalline nature was very obvious to the 

 unaided eye, though the crystals were small. 



