136 ANNUAL. REPORT OF THE Off. Doc. 



records show that bones and phosphatic marls were used centuries 

 ago to produce better crops, but they were used without Iinowledge 

 of their action, but simply as a result of accident or observation. 

 The present theory of the relation of plants and plant food has made 

 it possible to place this question of fertilization upon a more ra- 

 tional basis. The principle facts upon which our knowledge of the 

 whole field of agricultural chemistry is based are briefly stated 

 about as follows: Chemistry is that branch of natural science which 

 treats of the composition of matter and the changes which occur as 

 a result of alteration of the molecules. Chemistry recognizes seventy 

 some different elements. A chemical element is any substance 

 which can not by any known means be separated into two or more 

 different kinds of matter. Of the total number of elements known 

 to chemistry, however, only fourteen are required for the production 

 of plants. These fourteen are carbon_, hydrogen, oxygen, nitrogen, 

 potassium, phosphorus, calcium, iron, sulphur, magnesium, chlorin, 

 sodium, silicon and manganese. We are already familiar with the 

 fact that as far as the supply of these materials for use of the plant 

 is concerned, eleven of them are always present in suitable condi- 

 tion. The three which are often found to be deficient ^re nitrogen, 

 phosphorus and potassium, or as w^e are more familiar with them — 

 nitrogen, phosphoric acid and potash. In the present discussion we 

 will include only one of these fertilizing elements — phosphoric acid — 

 discuss its sources, forms and some phases of its uses. Phosphoric 

 acid, or rather the element phosphorus — is not only essential to plant 

 growth but the functions it performs in the plant are quite varied. 

 Phosphorus is found in large quantities in yeast cells, in the form- 

 ing seedS;, in the muscles of animals, and in all cases where special 

 demand for chemical activity is made. It is in the seed especi^Iy 

 that the influence of fertilization with phosphoric acid is most ap- 

 X)arent. Phosphoric acid is generally found combined with lime, 

 forming calcium phosphate or so-called bone phosphate of lime. It 

 is found in large quantities in several minerals and constitutes about 

 85 per cent, of the ash of bones. The chief raw materials which fur- 

 nish it for the manufacture of commercial fertilizers are bone, bone 

 black, phosphatic guanos, basic slag and rock phosphates. Bones 

 consist of two different kinds of material in addition to water. The 

 larger part consists of phosphate of lime, the other portion being 

 ossein or gelatine and fat. As bones come into the market for use 

 as fertilizers they vary greatly in composition according to the man- 

 ner in which they have been treated. Raw bone refers to bones 

 which have been ground in the raw state without previous treat- 

 ment. Raw bone contains 4.5 per cent, nitrogen and about 25 per 

 cent, phosphoric acid. They contain in this condition considerable 

 fat which is objectionable as it increases the diflBculty of grinding, 



