Brown.] ^38 [May IS, 



acid gas over the minerals at an elevated temperature. In these trials, 

 0.2 gram of the mineral was placed in a porcelain boat and heated in a 

 glass tube in a strong stream of the gas. The sulphur in the series of 

 experiments at the lower temperature was collected by passing the gas 

 through bulbs containing Br + HCl ; at the higher temperatures, the 

 residue in the boat was analyzed and the sulphur lost estimated by diifer- 

 ence. In the experiments at low temperature the entire tube was exposed 

 to a temperature of 210°, as determined by thermometer. The HCl was 

 passed over in a strong stream for one hour. The action at this tempera- 

 ture was slight ; the results obtained do not, however, show the entire 

 amount of sulphur removed, as some remained in the cool end of the 

 tube, from the dissociation of the hydrogen sulphide. As the action was 

 so slight, no attempt was made to collect and estimate this sulphur 

 remaining in the tube. In the bromine and hydrochloric acid solution 

 was found sulphur as follows : 



Pyriteat 210° in current of HCl (a) 0.94 



(6) 0.93 



Marcasite at 210° in current of HCl (a) 0.77 



(b) 0.59 



More marked results were obtained by increasing the temperature. 

 Similarly conducted experiments were carried out at 310° and 325°, the 

 time of healing ranging from one to three and one-half hours. The tem- 

 perature of 310° was graded by keeping it between the melting points of 

 NaHSO^-H.^0 (300°) and NaNOj (313°), the higher temperature was 

 between the last 313° and the melting point of KCIO3 (334°). After the 

 HCl had been passed for a sufficient length of time, the tube was allowed 

 to cool (with the gas current continued until cold) and then the remain- 

 ing sulptjur estimated by oxidizing the contents of the boat with nitric 

 acid and potassium chlorate and precipitating and weighing as BaSO^. 

 The amount found, subtracted from 53.33 fc, gave the loss of sulphur. 

 In this case the results obtained by oxidation were reversed, the pyrile 

 lost more sulphur than the marcasite. This is an expression of the fact that 

 the hydrochloric acid gas (or its contained CI) acts more vigorously on 

 the iron of pyrite than on that of marcasite. The results of the reaction 

 were in each case ferrous chloride in the boat and free sulphur in the 

 tube, the latter from dissociation of the hydrogen sulphide. Is'o ferric 

 chloride was seen in the tube, except a trace wiih the pyrite. Each min- 

 eral was heated f<u' one hour at 310° in a current of the gas and showed 

 loss of sulphur as follows : 



Pyrite heated at 310° for 1 hour in HCl, sulphur lost 10.73 



Marcasite " " " " " 7.19 



About the same relative amounts were lost on heating for three and 

 one half hours at 325°. The results thus obtained were as follows : 



Pyrite heated at 325° for 3^ hours in HCl, sulphur lost 17.13 



Marcasite " " •' " " 10.70 



