Moist- Combustion Process. 139 



high temperatures ; and on this occasion we wish to explain 

 this difficulty and how it has been overcome. 



The difficulty arises from the fact that, at temperatures very 

 little above 100° C, a mixture of pure permanganate of potash 

 and caustic potash evolves oxygen gas. This fact we have 

 very carefully ascertained, both by noting the diminution in 

 oxidizing-power which the solution shows after being heated 

 to 180° in the oil-bath, and by actually collecting and mea- 

 suring the oxygen gas which was evolved during the heating 

 in the oil-bath. The gas is evolved very freely at tempera- 

 tures even below 140° C; and the numerical results accord 

 very fairly with this equation : — 



2(KMn0 4 ) + 2(KHO) = 2(K 2 Mn0 4 ) + H 2 + 0. 



Here, as will be observed, the permanganate of potash is re- 

 presented as losing one fifth of its active oxygen, and yielding 

 manganate of potash. 



It has long been known that at very elevated temperatures, 

 at temperatures bordering on low redness, permanganate of 

 potash parts with oxygen and forms manganate of potash — 

 that, in point of fact, at these elevated temperatures manga- 

 nate, and not permanganate, is the stable form of combina- 

 tion ; but we believe this easy evolution of oxygen at tempe- 

 ratures a little above the boiling-point of water is quite a 

 novelty. For the moist-combustion process it would be a very 

 uncomfortable novelty if we were unable to stop the evolution 

 of the gas by a convenient device, since the alkaline perman- 

 ganate would cease to keep a trustworthy record of the con- 

 sumption of oxygen during the process. 



We have, however, to add that we can stop the evolution 

 in a most convenient manner. . We mix some hyd rated bin- 

 oxide of manganese with the permanganate and alkali ; and 

 then there is no evolution of oxygen. Why this addition 

 should be effective is obvious ; and the chemist will have no 

 difficulty in understanding that the necessity of having to 

 make such a condition does not damage our process. 



We have to record, as an interesting reaction, the behaviour 

 of green oxide of chromium with strongly alkaline solution of 

 permanganate of potash. It acts very readily, and yields 

 chromate of potash and hydrated binoxide of manganese ; this 

 takes place at temperatures even below the boiling-point of 

 water. We are following up this experiment, and hope to 

 make new and rare metallic acids. 



