[chadsey] decomposition OF POTASSIUM CHLORATE 27 



that even when most of the perchlorate has been decomposed, a con- 

 siderable amount of ohlorate remains. This is due to the fact, dis- 

 oovercd by Dr. Teed, and afterwards confirmed by Frankland and 

 Dingwall, that potassium perchlorate in its decomposition yields potas- 

 sium chlorate as one of its first products. It might be expected 

 therefore, that at temperatures above 500° little or no perchlorate 

 would be formed, or, if formed, that it would immediately decompose 

 to chlorate. Such, however, is very far from being the ease, as may 

 he seen in the diagram representing the formation of perchlorate. From 

 this we see that, whatever the temperature may be, the same percentage 

 of perchlorate is formed at some stage of the reaction, except in those 

 cases where, owing to the low temperature the reaction is very slow. 

 The perchlorate seems to reach a maximum of about 65 per cent of 

 the total chlorate heated. In the diagram we have represented the 

 weight of chlorate changed to perchlorate, and this multiplied by the 



ins-6 



fraction — gives the actual weight of the perchlorate. The highest 



number given in the diagram is 57-5, and, consequently, the greatest 



122-G 



percentage of perchlorate actually found is 57-5 x = 65. It 



■^ ° ^ -^ 138-6 



is possible that this is not the highest percentage that may be formed, 



for, owing to the conditions of the experiment it is manifestly almost 



impossible to interrupt the decomposition at the exact point at which 



the perchlorate content is highest. But a number of results obtained 



at different temperatures approximate to this value, and, in two cases, 



lines of extrapolation indicate practically the same height on the diagram 



as the maximum point. 



It seems beyond doubt, therefore, that, whatever the temperature 

 may be, the reaction at first proceeds toward the formation of a definite 

 maximum of perchlorate. If the temperature be sufficiently high, 

 the perchlorate is then decomposed into chlorate, chloride, and oxygen. 

 The only apparent difference in these cases is the difference in the 

 rate at whicli the reactions take place. At 550° the reaction has 

 advanced as far at the end of 15 minutes as in three hours at 500°. 

 The difference in rate between decompositions at 500° and dccomposi- 

 lici's at 5'0° is very much greater than that between those at 450° 

 and tlîose at 500°. A similar increase in rate for the next 50° would 

 mean tlin': the reaction had become explosive. Whether such an ad- 

 vance takes pliice has not ueen tested, but it is improbable that it 

 does so. 



It would di- ' tless be incorrect to suppose that none of the per- 

 chlorate is f"'opr,m'' "] until th3 maximum amount has been formed. 



