200 



Allen, Crenshaiv, Johnston, and Larsen — 



ture and pressure. The discontinuity in the curve between 

 1165° and 1200° which is conditioned by the change of state 

 will be discussed later (p. 207). 



Maximum percentage of sulphur in pyrrhotite. — The most 

 concentrated solution of sulphur in ferrous sulphide obtained 



Fig. 8. Curve in space showing the dependence of the composition of 

 pvrrhotite on temperature and pressure. 



C (composition) = percentage of dissolved sulphur. 

 P = pressure in millimeters of mercury. 

 T = temperature. 



synthetically contains 6 per cent of sulphur and 94 per cent of 

 FeS. This solution was obtained at 600°, where the absorption 

 of sulphur from hydrogen sulphide is slow. At 575° the 

 reaction was so slow that the attempt to get a saturated product 

 was discontinued. At 550°, as we will show farther on, 

 pyrite is formed. The curve in fig. 9 shows an extrapola- 



