202 TILLERS OF THE GROUND .CHAP. 



carefully examined the results of the burning, his 

 examination being of the kind which a chemist 

 calls an analysis. What he found in the first place 

 was that the results of the burning were, roughly 

 speaking, always the same. Whether the plants 

 grew " on the most diversified soils, in the most 

 varied climates, whether cultivated on plains or on 

 high mountains," the same effects were produced 

 when they were burned. 



What was the effect of the burning ? In the 

 first instance he found that the burning plant gave 

 off a colourless gas, which stifles animals ; this gas 

 we call carbonic acid gas. Secondly he found that it 

 gave off small quantities of a gas called ammonia 

 the gas which brings the tears to our eyes when we 

 take a big sniff of a bottle of smelling-salts. 



When the plant had quite burnt away, Liebig 

 found that there was left behind a little mass, of 

 greyish ash, like that which is left when wood burns 

 away. In this ash he found what the chemist calls 

 salts,^ salts of potash, lime, magnesia, and so on. 

 Liebig said, therefore : All plants contain carbonic 

 acid gas, ammonia, and salts. He knew, however, 

 that ammonia does not occur in the living plant. 

 It is the proteid of the living plant which makes 

 ammonia when the plant is burnt. 



He knew also that the carbonic acid gas produced 

 by plants when they are burnt is got from the air ; 



