400 Allen , Crenshaw, and Merwin — 



open at the top. The side tube was sealed direct to one arm 

 of a U-tube of the same diameter (5 mm ) stuffed with glass wool. 

 The U-tube was about 18 cm high and during the experiments 

 was surrounded by ice to condense any free sulphur. The 

 other arm of the U-tube was sealed to the absorption tube. 

 This was about l ctn in diameter drawn down to 5 mra at either 

 end and contained a layer of pure solid caustic soda about 6 cm 

 in length, which was kept in place by plugs of glass wool. 

 The free end of the absorption tube was sealed to a May-Nel- 

 son vacuum pump. When the apparatus was made ready the 

 sulphide was dropped through a small funnel into the vertical 

 tube, which was then sealed off at the constriction. 



The sulphide was heated by a small resistance furnace by 

 which the vertical tube was surrounded. The apparatus was, 

 of course, evacuated before the heating began and the pump 

 was kept running during the experiment.* The temperature 

 in all the experiments, where not otherwise stated, was carried 

 to 600° measured by a thermoelement, the hot junction of 

 which touched the glass on the outside of the tube close to the 

 sulphide. The time required to reach this temperature was 

 about three-quarters of an hour. The current was then turned 

 off, for under these conditions considerable decomposition of 

 the disulpkide into pyrrhotite and sulphur always took place, 

 thus leaving no reasonable room for doubt that all the gas was 

 driven off. 



After the heating was over, the furnace was removed and 

 the tube quickly cooled, air was admitted to the apparatus, the 

 absorption tube cut out, the soda dissolved in water and freed 

 from glass wool by filtering. The solution was then tested 

 with cadmium chloride and if yellow cadmium sulphide came 

 down, a sufficient excess of the reagent was added, the precipi- 

 tate filtered and washed, and finally dissolved in ammonia and 

 perhydrol. The solution was then just acidified and precipi- 

 tated hot with barium chloride. After the nature of the sul- 

 phur compound had been sufficiently well established the use 

 of the cadmium salt was omitted and the soda solution directly 

 oxidized by perhydrol. 



The results are shown in Table III. All the synthetic sul- 

 phides gave off hydrogen sulphide when heated, but the facts 

 plainly indicate that this was not present originally in the sul- 

 phide, but was formed by the action of water, during the heat- 

 ing, on the pyrrhotite, one of the decomposition products of 

 the disulphide ; f for when pure natural marcasite was ground 



* None of the gas escapes by this method. In the last experiment in 

 Table III, the apparatus was isolated from the* pump by a stopcock after 

 evacuation and before heating. The results were practically the same. 



f When the maximum temperature was only 350°, much less pyrrhotite 

 was formed and far less sulphur was obtained. 



