1S94. 



233 



[Brown. 



permanganate solution, after it had acted the required time, was treated 

 as in the experiments conducted at ordinary temperatures described above. 

 Much more active oxidation toolv place at this temperature (100^), but 

 the tendency of the mineral to cake together was much more marked, 

 and now this took place with pyrite as well as with marcasite. Moreover, 

 the deposition of manganese dioxide in every case was now very great, 

 causing often a stoppage of the oxidation until it could be dislodged. As 

 these oxidation exj^eriments had already occupied much time only one 

 trial was now made at each concentration of solution for each hour from 

 one to five, unless, as before, marked discrepancies occurred, when two 

 or more trials were made. The series of results are hence not so regular 

 as they would have been had more trials been made, these irregularities 

 arising from the difficulties that have been mentioned, as well as from the 

 fact that the dilute solutions soon became exhausted, and that all solutions 

 sufTered some evaporation, but some more than others, causing irregular 

 strength with the same solution. Nevertheless, the results agree in kind 

 with those obtained at ordinary temperature, but diflfer widely in degree. 

 Whereas at ordinary temperature the greatest amount of sulphur oxidized 

 in marcasite by the five-hour trial with o per cent, permanganate was 4.17 

 per cent., at 100° this became 16.86 per cent, or about four times as much. 



Action of jig Normal Potassium Peiimanganate Solution at 100°. 



The results given in the following table show perhaps more strongly than 

 either of the other series of experiments at 100° the effect of the different 

 disturbing causes that have been mentioned. It especially shows the 

 effect of caking of the pyrite, which now came in as an important dis- 

 turbing factor. The result of this caking is shown in the three- and four- 

 hour results with pyrite, both being very low. Marcasite, on the other 

 hand, invariably caked and stuck to the bottom of the bottle, but as this 

 was a constant source of error in this case, the results show a gradual and 

 fairly even increase. Irregular results with marcasite were now largely 

 conditioned by the evaporation of the solution or by the fact of whether 

 the mineral was evenly caked over the inner surface of the vessel or con- 

 centrated in spots. The result of this latter way of caking will be better 

 seen in some of the subsequent series of experiments. 



Table Showing the Relatice Oxidation of Sulphur in Pyrite aud Marcasite 

 by a T^g- Normal Solution of KMnO^ at 100^ C. 



