138 VecoDiposifion of Iron Pyrites. 



tlie mineral, about 3 grams, was placed in a glass-stoppered bot- 

 tle, with the addition of nitro-hydrochloric acid and bromine, 

 inserted in a beaker of water, and covered by a smaller inverted 

 beaker, to make a water-joint for safety, and tlins digested upon 

 a water-bath until complete solution. This was then diluted 

 and divided. In one pai-t, the iron was determined volumetri- 

 cally in the usual way, by means of potassium permanganate. 

 To the other, citric acid was first added to retain the iron in solu- 

 tion and the sulphuric acid was precipitated by a slight excess 

 of barium chloride. After thorough washing, this precipitate 

 was purified by Stolba's method, by digestion in copper acetate, 

 washed and weighed, then fused with mixture of sodium-and 

 potassium-carbonates, leached out with water, the other solution 

 treated with bromine, the residue and filtrate separately acid- 

 ified, the two solutions heated on the water-bath and combined, 

 and the re-precipitated barium sulphate again thoroughly 

 washed, dried and weighed. In all cases the first precipitate 

 was found before the fusion to contain a small proportion of 

 barium-salt as impurity, and in one case a coloration produced 

 by copper derived from the copper acetate. Of the analyses pre- 

 sented below, Nos. 1 and 2 were made upon the finely pulver- 

 ized mineral, N'o. 1 having been weighed immediately after ])ul- 

 verization, and No. 2 about three-quarters of an hour after- 

 wards. In both, it will be noticed that the amount of sulphur 

 is considerably less than that demanded by the theoretical con- 

 stitution of the mineral, especially in No. 2, whose material was 

 longest exposed to the air. A series of a dozen samples of i)y- 

 rite and marcasite, in finely divided condition, had been already 

 exposed to the air, and it was found that these manifested inci- 

 pient decomposition in all cases, often within one or two hours, 

 by a caking of the powder and a distinct sulphurous odor. A 

 portion of the Folkestone marcasite, about 0.2 gram, was also 

 enclosed with 2 c. c. of concentrated hydrochloric acid, in a her- 

 metically sealed tube ; the mineral had been, previously exposed 

 to the air for several hours, in the state of a fine powder. In an- 

 other tube, a freshly broken pure lump of the mineral was di- 

 gested in the same way. The former immediately yielded a yel- 

 lowish solution, revealing the presence of iron-oxide from par- 

 tial oxidation of the exposed powder ; however, on hanging a few 

 days in the sunlight, the solution gradually lost its color, appar- 



