THE DEVELOPMENT OF AGRICULTURAL CHEMISTRY 5 



which of them contributes most to that increase of food: nitre, water, 

 air, fire, and eartli." 



During the latter half of the eighteenth century a considerable in- 

 terest was manifested in all phases of agriculture. Textbooks were 

 written, experimental work was stimulated, and societies were formed 

 for the promotion of agriculture. In 1755 the Edinburgh Society of 

 England employed a chemist by the name of Francis Home "to try how 

 far chemistry will go in settling the principles of agriculture." Home, 

 believing that the whole system of agriculture was dependent upon 

 plant growth, prosecuted his research along the lines of plant nutrition, 

 finally drawing the conclusion that there were at least six plant-food 

 materials: air, water, earth, salts of different kinds, oil, and "fire in a 

 fixed state." After the work of Home there was no important advance 

 in agricidtinal chemistry for 40 years. From what has been stated, it is 

 evident that anything like an adequate idea of the growth and com- 

 position of plant bodies could not be obtained until certain of the im- 

 portant chemical elements had been discovered and the composition of 

 water and other common substances had been established. 



During the period 1770 to 1800 some of this necessary work was ac- 

 complished, but its importance in agriculture was not appreciated at 

 the time. This work, the discovery of oxygen by Priestley and by 

 Scheele, the discovery of the composition of water by Cavendish, and 

 the explanation of combustion by Lavoisier, served to open the way 

 for the development of what we consider modern chemistry. 



After the work of Home further progress in scientific agriculture was 

 hardly possible until greater use was made of accurate chemical meth- 

 ods of investigation. Although Ingen-Housz receives credit for the dis- 

 covery of the role that carbon dioxide plays in plant economy, it re- 

 mained for De Saussure to place this discovery on a firm scientific basis 

 by the use of quantitative methods. His book, Researches upon Vege- 

 tation, published in 1804, was really the first scientific work showing 

 the source of the carbon compounds in plants. He established, by 

 means of quantitative experiments, that the increase in the amounts 

 of carbon, hydrogen, and oxygen, when plants were exposed to sun- 

 light, was obtained from the carbon dioxide of the atmosphere and 

 the water of the soil. This early investigator also stated that the 

 mineral elements derived from the soil were essential to plant growth. 

 In proof of this point he gave the results obtained for the analyses of 

 the ash of many different plants. He believed that plants obtain the 

 greater part of their nitrogen from the soil. These views of De Saus- 

 sure have since been investigated and verified by many different scien- 

 tists and are substantially those held at the present time regarding the 



