No. 4.] KEEPING UP FERTILITY. 103 



he said that he had been am})ly repaid for the expense and 

 trouble of coming to Amherst. 



Raw Materials and Chemicals. 



Eitlier of the terms "raw material" or "chemical," as 

 applied to the numerous substances most of which furnish 

 but one or two of the important elements of plant food, is in 

 a certain sense ina|)propriate. ]\Iany of them are directly 

 incorporated in mixed fertilizers. They are no more "raw" 

 before mixing than after. Dried blood and dry ground fish 

 are examples. The term "chemical" is appropriately 

 applied, perhaps, to substances like muriate of potash, sul- 

 phate of potash and nitrate of soda, which have been subjected 

 to a chemical process of manufacture before being put upon 

 the market ; but these are chemicals to precisely the same 

 extent after mixture in the complete special feililizers. They 

 do not undergo any further chemical change. They are 

 simply mechanically mixed with other materials. I prefer 

 the term "unmixed fertilizers." All may properly be 

 included under this single head, for all have a fertilizer 

 value. They differ, indeed, very widely in their degree of 

 availability, as well as in other qualities. Some are almost 

 entirely unavailable, such, for example, as leather and 

 apatite. These might properly be called "raw," because it 

 is best to subject them to special treatment before applying 

 them to the land. Others, like nitrate of soda and super- 

 phosphates, are immediately available. Between the two 

 extremes we have every possible degree of availability. I 

 shall consider separately materials valuable chiefly for 

 nitrogen, for phosphoric acid and for potash. 



NiTROGEx Fertilizers. 

 Some of the more important materials which are used 

 chiefly as a source of nitrogen mentioned in the probable 

 order of their availability are nitrate of soda, sulphate of 

 ammonia, dried blood and flesh meal. Besides these there 

 are a number of animal sul)stances rich in nitroofen but also 

 containing consideral)le phosphoric acid. The more im- 

 portant are dry ground fish, tankage and bone meal. 

 Cotton-seed meal, though less generally used, except by 



