

CHEMICAL MANURES. 



position of which is analogous with the earthy parts of bone. Such 

 are, briefiy summarized, the chief historical facts regarding the 

 discovery of phosphorus and phosphoric acid in the three kingdoms 

 of nature. Since then chemists have continued their investigations ; 

 they have searched for this substance everywhere, and they have 

 found it more and more as analytical methods have been improved. 

 Its presence in urine and in bones led to its presence in all the 

 fluids and organs of man and animals being suspected, and very 

 soon it was found to be so. It was found in all plants and in all 

 their organs. It was thenceforth recognized that the phosphorus 

 contained in the body of animals was of vegetable origin. But 

 from whence do plants derive this substance ? The answer to that 

 question was sought for a long time. Even up to the middle of 

 the eighteenth century, when scientists like Saussure (1740-1799) 

 and others were led by simple logic to look for phosphoric acid in 

 the soil, agronomists persisted in regarding it as a derivative of 

 other substances, because very little of it was found in the soil, and 

 this little might very well be brought on to the land by farmyard 

 ■dung. However, improved analytical methods were bound gradu- 

 a,lly to elicit the truth. 



Origin and Distribution of PhospJioric Acid in Nature. — If it 

 be interesting for the farmer and the chemist to follow the migrations 

 of an air-bell, and the curious phenomena under the influence of 

 which the molecule of nitrogen becomes successively ammonia or 

 nitric acid, then vegetable organism, then finally muscular fibre, it 

 is none the less instructive to follow the migrations of the molecule 

 of phosphorus. Let us endeavour to grasp these migrations, and 

 to trace them, starting from the point of origin of phosphoric acid, 

 i.e. the presence of this body in the primitive and crystalline rocks. 

 The analysis of the primitive rocks, and of the metalliferous veins 

 which they contain, proves that phosphoric acid is almost always 

 one of their constituent elements. ^ Associated with lime, the 



1 The two men of science who studied the question most profoundly were 

 Forchammer of Copenhagen and Stockhardt of Germany. The latter found 

 phosphoric acid in several rocks in which it was believed to be absent. The 

 I)ercentages of phosphoric found in different rocks are as follows : — 



TABLE L— PERCENTAGE OF PHOSPHORIC ACID IN VARIOUS 



ROCKS. 



