28 BOARD OF AGRICULTURE. [Jan. 



count for the results, and hence the phosphoric acid must be 

 regarded as the valuable constituent of bones. This was the 

 reasoning which led to the true theory of the action of bone ; 

 the date of this conclusion is from 1830 to 1835. 



We find mention of the use of " saltpeter," or nitrate of 

 potash, in 1625, but there are no definite records until 1825 

 to 1829. 



In 1836, an effort was made by an English farmer to de- 

 termine the true cause of the wonderful eflTects of "salt- 

 peter." He knew that this manure contained nitric acid, 

 combined with potash, and he planned an experiment on 

 grass. Three equal areas were measured off and were 

 treated as follows: No. 1, watered daily with pure water; 

 No. 2, watered daily with water in which potash was dis- 

 solved ; No. 3, watered daily with water with which a little 

 nitric acid was mixed. The result was that No. 1 gave the 

 least yield, No. 3 was increased considerably, and No. 2 still 

 more. This experiment showed that the nitrogen of the 

 nitric acid and the potash were each useful to the growing 

 grass. Thus it was established, by practical farmers, that 

 nitrogen, phosphoric acid and potash are forms of plant food 

 that exhausted soils need. 



The second question mentioned at the commencement of 

 this talk concerning the services of plant food, was this : 

 "Where shall we get the materials they [plants] 



NEED ? " 



Phosphoric Acid. 

 Bone, as already stated, was the first source of this variety 

 of plant food. The following tabulated statement shows the 

 probable date of use and discovery of materials containing 

 phosphoric acid : — 



1750. Bones first used in England. 



1814 First bone mill used in England. 



1780. Bones first used in United States. 



1820. First bone mill used in United States. 



1837. South Carolina rock first mentioned. 



1839. Liebig suggested the use of sulphuric acid to dissolve bone. 



1840. Dissolved bone first used. 



1843. Spanish phosphate rock first mentioned. 

 1845. Spanish phosphate rock first used in England. 

 1861. Dissolved bone first used in United States. 



