12 ELEMENTARY AGRICULTURAL CHEMISTRY 



potassium chlorate is to expel all the oxygen and to leave a 

 residue of potassium chloride, KCl. The reaction is therefore 

 represented by the equation 



2KC103=2KCl + 30,. 



The operation can be conducted in a hard glass flask or retort, 

 and the gas collected over water, in which it is only sparingly 

 soluble. If manganese dioxide, Mn02, be mixed with the 

 potassium chlorate the latter yields its oxygen at a much lower 

 temperature, and without fusion. A curious fact is that in 

 such a case the potassium chlorate is alone affected, the 

 manganese dioxide remaining unchanged at the end of the 

 operation. Oxygen compressed into steel cylinders is now 

 an article of commerce. Most of the oxygen so supplied is 

 prepared from the air by a process known as Brin's. This is 

 based upon the behaviour of barium monoxide, BaO, when 

 heated in air. Under proper conditions oxygon is absorbed 

 and barium dioxide or peroxide, BaO,, is formed, the other con- 

 stituents of the air passing away unchanged. By the action 

 of a higher temperature or lower pressure the barium dioxide 

 decomposes into the monoxide and free oxygen. The barium 

 monoxide is then again ready to absorb a fresh portion of 

 oxygen from the air, and so the process can go on almost in- 

 definitely. The reactions involved may be thus represented : — 



(1) 2BaO -f 02 = 2BaO, 



from the air 



(2) 2BaO, = 2BaO + 0, 



the equations in this case being simply reversed. The appa- 

 ratus employed on the large scale is ingenious and somewhat 

 complicated. 



Oxygen is a colourless, odourless gas, very slightly soluble in 

 water, 100 volumes of water under ordinary conditions dis- 

 solving about 4 volumes of the gas. It shows a great tendency 

 to combine with other substances, and the act of union is usually 



