CHAPTER VI. 



Experiments with sulphuric acid and with the sulphates of potash and soda. 

 Proportion of sulphur in all crops. Kecorded experiments with sulphuric 

 acid. Suggestions for experiments with this acid. Composition and general 

 properties of the sulphates of potash, soda, lime, magnesia, and iron. Results 

 of experiments with the sulphates of potash and soda. Functions performed 

 in the soil by these substances. Suggestions for experiments with the sul- 

 phates of potash and soda applied alone. 



1. Proportion of sulphur contained in our usually cultivated 



crops. 



SULPHUR is an indispensable constituent of all cultivated crops. 

 Some contain more of it, and some less ; but all require it for 

 their healthy growth, and all obtain it from the soil by their 

 roots. Nearly all soils contain this sulphur in considerable 

 proportion in some of its forms of combination, though, as 

 appears to be the case with every other kind of food necessary 

 to vegetation, it is more easily attainable by the plant, or exists 

 in a more available form in some soils than in others. The 

 important part which this elementary substance plays in the 

 economy of organised nature, may be inferred from the fact, 

 that the wool alone which clothes the sheep now existing in 

 Great Britain, contains Jive millions of pounds of sulphur as 

 much as is contained in 30 millions of pounds of gypsum.* All 

 this sulphur is extracted from the soil in the herbage cropped 

 by the sheep; the soil, therefore, must contain naturally an 

 almost inexhaustible supply of it, or must have the annually 

 diminishing supply renewed by natural or artificial means. 



Messrs Way and Ogston have recently published a series of 

 determinations of the quantity of sulphur contained in several 



* Johnston's Elements of Agricultural Chemistry and Geology, 5th edition, p. 329. 



