FIXATION OF NITROGEN 47 



German professor Liebig presented to the British 

 Association the famous report afterwards published 

 as a book on Chemistry in its Application to Agri- 

 culture and Physiology. By applying the exact 

 methods of chemistry to agriculture Liebig succeeded 

 in establishing that plants derive the Carbon of 

 their tissues from the Carbon Dioxide of the air, and 

 not from the Carbon compounds that may be present 

 in the soil. He did more than this, for he pointed 

 out that " the crops on a field diminish or increase 

 in exact proportion to the diminution or increase of 

 the mineral substances conveyed to it in manure." 

 In one essential point, however, he fell into error. 

 He came to regard the Ammonia of the air as analo- 

 gous with the Carbon dioxide in the air, and preached 

 the doctrine that the plants were able to derive their 

 nitrogenous food from the atmosphere. In the 

 Farmer's Magazine, for instance, he wrote : 



" If the soil be suitable, if it contains a sufficient 

 quantity of alkalis, phosphates, and sulphates, 

 nothing will be wanting. The plants will derive 

 their Ammonia from the atmosphere as they do 

 Carbonic Acid." 



Liebig's discoveries were of classic importance, 

 partly because of the valuable contribution they 

 made to agricultural knowledge, but still more 

 because of the stimulus they gave to agricultural 

 research along exact lines of experiment. He had 

 not, however, found the whole truth. His patent 

 manure, when tried in the field, was a failure, partly 

 because he presented his mineral foods to the plants 

 in forms unsuitable for their absorption, and partly 



