107 

 Studies in Catalysis. 



By James H. Ransom. 



In l'J02 there was presented to this Academy by Mr. E. G. Mahin, 

 -working in my laboratory, a paper dealing with the action of heat on 

 mixtures of manganese dioxide and potassium chlorate. In this paper 

 it was shown that the nature of the reaction as well as the temperature 

 of decomposition depended on the purity of the oxide, in that the purer 

 and drier the material the higher the temperature of rapid decomposition 

 and the smaller the amount of chlorine and chlorine oxides. The study of 

 this action has been continued by the writer, and some new data accumu- 

 lated. 



Instead of using the puritied commercial article, manganese dioxide 

 was prepared in the laboratory by heating chemically pure manganous 

 nitrate to a high temperature as long as decomposition occurred, and 

 then washing out all soluble material. After this treatment the residue 

 was dried for some hours at a high temperature in vacuo. It was tlien 

 preserved in glass-stoppered bottles in a desiccator. Prepared in this 

 way the oxide is not hygroscopic. 



One to two grams of potassium chlorate, free from chlorides, was 

 mixed with about the same weight of the manganese dioxide and the 

 mixture heated in an air-bath, the temperature being controlled with a 

 gas regulator. With the purified material there was observed little or 

 no decomposition at 170° (as Mahin found), and only at 245° to 260° 

 was the action at all perceptible. At 300° to 310° the action completed 

 itself in a few minutes. It was observed that while little oxygen was 

 evolved below 245° the residue gave a test for chlorides, though the 

 tests made before heating gave wholly negative results. Some of the 

 experiments showed less loss in weight during heating than that corre- 

 sponding to the chloride found by titration against standard silver nitrate. 

 Occasionally, however, the loss was even greater than that calculated 

 so that it was felt that great reliance could not be placed in the difference 

 in weight, especially as the tubes were often heated continuously for some 

 days. The evidence of decomposition rests, therefore, on the formation 

 of chloride. 



After these facts were established twenty experiments were per- 

 formed to find the amount of chloride produced at different tempera- 



