1894.] 'J [Brown. 



mediate use (o avoid any chance of oxidation of the ground material ; 

 the stock samples of the two minerals broken to nul size were kept in 

 stoppered bottles. The grinding of material was continued as long as 

 grit appeared, but no bolting was resorted to. 



As the experiments of Prof. Smith on oxidation by the electric current 

 showed such remarkable results, my first experiments were on oxidation. 

 As an oxidizing agent potassium permanganate (KMiiO^) was used, sev- 

 eral strengths of which were tried for varying intervals of time with each 

 mineral, and the amount of sulphur oxidized to sulphuric acid determined 

 in the liquid by precipitating as barium sulphate. Tlie object was to 

 secure a complete series of results which would show the comparative 

 rates of oxidation of the sulphur in the two minerals, i Neutral aqueous 

 solutions of the potassium permanganate were used, and the strengths 

 of solution employed were j^^ normal, one per cent., three per cent, and 

 five per cent.; the periods of oxidation extending over one, two, three, 

 four and five hours, and the entire series being performed at ordinary 

 temperatures and at 100°. As duplicate determinations were made in the 

 majority of cases (I made about 130 determinations of su'phur as barium 

 sulphate), this work consumed a large amount of time and prevented as 

 full a study of some other reactions of the two minerals as had been orig- 

 inally intended. The following are the detailed descriptions of mj'' pro- 

 cesses and results : 



Action op yj^ Normal Potassium Permanganate Solution at 

 Ordinary Temperature. 



These oxidations were performed as follows: Two-tenths of a gram 

 of the finely powdered mineral was placed in a stoppered bottle of about 

 100 c.c. capacity, then 50 c.c. of the permanganate solution added and 

 the contents of the bottle violently shaken to break up lumps. This 

 shaking was repeated about every fifteen minutes while the oxidation 

 lasted. The temperature of the room was at the same time recorded. As 

 stated, the oxidation was continued for one, two, three, four and five 

 hours with each mineral, making at least ten experiments necessary for 

 each strength of solution. After the solution had acted for the required 

 time it was rapidly filtered through asbestos with aid of the filler pump, 

 the filtrate transferred to a beaker, 20 c.c. of concentrated hydrochloric 

 acid added, and the whole heated until all manganese was reduced to 

 manganous chloride. If not too acid the solution was then diluted to 

 about 300 c.c. and the sulphuric acid precipitated as barium sulphate. 

 When very acid, excess of hydrochloric acid was removed by evaporation 

 or by adding ammonia, the ammonium chloride seeming to facilitate the 

 precipitation. The precipitate was washed with hot water and then 

 w^eighed. All precipitations were made at boiling temperature and di- 

 gested hot for at least two hours, and then cold for at least twelve hours 

 more before filtering. The filtrates from most of the cold tests were re- 



