8 GENERAL BIOCHEMISTRY 



the green pigment, chlorophyll, in this synthetic process. It remained 

 for Willstatter and his students to shed further light on the chemical 

 composition of chlorophyll. 



One of the earliest chemists who exerted a real influence on Ameri- 

 can agriculture was Samuel L. Mitchell, who held the chair of chemis- 

 try and agriculture at Columbia College from 1792 to 1801. Mitchell 

 helped to found the New York Society for the Promotion of Agricul- 

 ture, Manufactures and the Useful Arts, and through his efforts con- 

 siderable interest was developed in the use of gypsum as a fertilizer. 



In 1806, Thomas Ewell, of Virginia, published an important treatise 

 in which he stated: 



Agriculture is most intimately connected with chemistry. The power of 

 seed to attract and unite to parts of the soil, so as to vegetate or increase in 

 bulk, is purely chemical. Chemical knowledge will teach the gardener and 

 farmer what particular soil is best adapted for particular seed; it will teach 

 the way of forming soils for foreign plants; of making manures to the greatest 

 advantage; of preserving grains, roots, etc.; of destroying the insects; and 

 of correcting the disorders injuring the valuable shrubs. 



In 1810 Gerard Troost, a Dutch physician, emigrated to this coun- 

 try. He not only conducted what appear to be the earliest studies of 

 the composition of Pennsylvania soils, but also made valuable con- 

 tributions to agriculture, mineralogy, and geology in Tennessee. 



In 1842 Samuel Luther Dana published his Muck Manual, which 

 exerted a tremendous influence on New England agriculture for the 

 next twenty years. The period 1840 to 1850 was marked by a consider- 

 able increase in scientific and industrial activities. Chemists were busy 

 studying the chemistry of soils, crops, foods, and fertilizers. 



Our brief description of prominent agricultural chemists will not be 

 complete without the mention of Evan Pugh, the first president of 

 The Pennsylvania State University. His well-known treatise entitled 

 "Sources of the Nitrogen of Vegetation" established him as a leader 

 among the agricultural scientists of his time. Although Dr. Pugh's 

 researches were not nimierous, they were characterized by an unusually 

 high quality of skill and accuracy. His administrative record at The 

 Pennsylvania Agricultural College was no less brilliant, and the 

 organization of the college curriculum, the inauguration of research, 

 and the high standards set by Dr. Pugh at that early date will always 

 stand as monuments to his memory. 



Samuel W. Johnson of Yale undoubtedly exerted a greater influence 

 than any other agricultural chemist of his time. Although Johnson 



