THE DEVELOPMENT OF AGRICULTURAL CHEMISTRY 7 



rather tlian from the carbonic acid from the soil. r)efore this time 

 many workers adhered to the humus theory of Thaer. The pubHca- 

 tions and lectures of Boussingault and De Saussure had made little im- 

 pression on the proponents of the humus theory. After Liebig's tirade, 

 there were few who dared to oppose his theory of carbon dioxide as- 

 similation. In the first edition of his book Liebig called attention to 

 the fact that farms from which certain products were sold gradually 

 became less productive because of the decrease of nitrogen, but he 

 made one serious mistake. He overestimated the amount of ammonia 

 present in the atmosphere and underestimated the value of nitrogen in 

 the soils and manures. A study of the chemical composition of the 

 ash of plants was also made by Liebig. His results led him to propose 

 the mineral theory of plant nutrition. Previous to this time De Saus- 

 sure had proved that plants contained certain mineral elements, but he 

 had laid no emphasis upon their importance as plant foods. Liebig's 

 publications on the composition of the mineral substances present in 

 plants and his emphasis on their importance as plant foods led to the 

 commercial preparation of manures, which in later years has developed 

 into the great commercial fertilizer industry. 



In 1837 John Lawes began a series of experiments on the application 

 of various manures to potted agricultural plants on his home farm at 

 Rothamsted, England, He soon discovered that to carry on his work in 

 a proper manner he needed the assistance of a trained chemist and 

 engaged the services of J. H. Gilbert, one of Liebig's former students. 

 Thus in 1843 the second agricultural experiment station was estab- 

 lished at Rothamsted. It is still in operation at the present time, hav- 

 ing been endowed with funds by John Lawes. Many of the Rotham- 

 sted experiments have been conducted continuously since 1844, and 

 results of the greatest value to agriculture have been obtained as a 

 reward of the earnest, persistent work of Lawes and Gilbert. 



Our modern science of bacteriology is, in a large measure, the out- 

 growth of the early work in agricultural chemistry. As men studied 

 and worked they found that chemical explanations were not sufficient, 

 and from the earliest times until the present the chemist has made use 

 of all the other sciences, indiscriminately, to aid in the solution of his 

 problems. 



The pioneers in agricultural chemistry first confined their attention 

 to the chemical phases of plant growth. Ingen-Housz and De Saussure 

 showed that atmospheric carbon dioxide is the source of carbon in 

 plant compounds. Later Lommel and Pfeffer emphasized the impor- 

 tance of light in the synthesis of organic compounds in the plant, and 

 Sachs, Leow, Baeyer, and others pointed out the important function of 



