270 



MR. V. H. VELEY ON THE CONDITIONS OF THE 



advisable not to completely dry the tinely-clivided metal, so as to avoid a possible 

 absorption of oxygen. 



The effect of platinum black is most striking; the interval of time is reduced 

 practically in the ratio of 5 : 3, even though the temperature was lowered 18, in 

 order to obtain a rate of decomposition sufficiently slow for convenient observation. 



Decomposition of Potassium Chlorate into the Perchlorate, Chloride, and Oxygen. 



2KC1O 3 = KC10 4 + KC1 + O 2 . 



It is usually stated in the more recent text-books on chemistry (see page 259), 

 that finely divided chemically inert substances do not accelerate the evolution 

 of oxygen from potassium chlorate. To decide this point a quantity of potassium 

 chlorate was re-crystallised ; into two similar-shaped retorts were introduced 

 70 grams of the salt ; to one portion 7 gram of precipitated barium sulphate 

 was added. The retorts were placed side by side in a small square air bath, provided 

 with two holes in one side, through which the necks of the retorts passed. The air 

 bath was packed with asbestos, to distribute the heat of the lamp as uniformly as 

 possible. After the evolution of oxygen had commenced, but before systematic 

 observations were taken, 104 c.c. of gas were given off from the chlorate containing 

 the barium sulphate, but only 51 '2 c.c. from that without the sulphate. The 

 observations are divided into sets of 50 c.c. each, being the capacity of the two 

 graduated tubes which served to collect the oxygen. The time was noted at which 

 each measure of oxygen was evolved from the retort containing potassium chlorate 

 and barium sulphate, and simultaneously the volume which had been evolved from 

 the retort containing potassium chlorate only was read. 



