54 CHEMISTRY. 



52. Preparation of Oxygen from Potassium Chlorate. The 

 most common way of obtaining this gas is by heating a 

 substance called potassium chlorate. This contains a large 

 quantity of oxygen. In every hundred grammes of it there 

 are thirty-nine grammes of this gas. This is more than four 

 times as much as there is in the mercuric oxide, the sub- 

 stance from which Priestley obtained the oxygen for his 

 experiments. Over a gallon and a half of oxygen can be 

 obtained from an ounce of potassium chlorate. There is only 

 a little more of this gas in this substance than in the diox- 

 ide of manganese ; but the former gives up all its oxygen 

 on being heated, while the latter, as we told you in 51, gives 

 up but a third part of what it contains. And, besides, the 



potassium chlorate 

 needs to be heated 

 but little compared 

 with the manganese 

 dioxide to evolve 

 the gas. The heat 

 of a spirit lamp or 

 of a Bunsen burner 

 is sufficient. Fig. 6 

 shows the method 

 of generating and 

 collecting the gas. 



53. Explanation of the Process. The potassium chlorate 

 is composed of three elements the two gases, oxygen and 

 chlorine, and the metal potassium, in the proportion KC1O 3 . 

 The oxygen is driven off by heat, and the chlorine remains 

 united with the potassium, making what we call potas- 

 sium chloride. Expressed in formulae thus: KClO 3 +heat 

 KCl-f-O 3 . Of chlorine and potassium we shall speak par- 

 ticularly hereafter. There is some danger of explosion in 

 obtaining oxygen from potassium chlorate alone, because 





