MANURES. 



37 



is necessary for its very existence that this minute supply 

 should be at that precise spot. (Liehig.) 



Phosphates, then, to produce their best effect, must be 

 made soluble, as it is only in this state that they can pene- 

 trate every portion of the soil. Broken bones dissolve 

 and part with their phosphoric acid very slowly in the 

 soil, but what good effect they produce continues a long 

 time. If finely ground, the present good effect is much 

 more evident. By mixing them in this state with sul- 

 phuric acid, it combines with a portion of the lime, con- 

 verting it into gypsum or sulphate of lime ; while the rest 

 remains in combination with the phosphoric acid as a bi- 

 phosphate (superphosphate) of lime. This is soluble in 

 water, and when applied to the soil is diffused through it, 

 and can be readily, and if not in excess, soon totally 

 absorbed, by the rootlets of growing plants, and conse- 

 quently its good effects upon the soil will soon disappear. 

 One peck of bones, thus prepared, will have as much pres- 

 ent effect as 16 bushels of ground bones undissolved. 

 (Lindley.) 



The soluble phosphates, in estimating the values of ma- 

 nures, are now regarded as the most important ingredient, 

 next to ammoniacal salts, and, as before stated, are often, 

 indeed, more necessary to supply. 



Sulphur* — Plants contain, either deposited in their roots 

 or seeds, or dissolved in their juices, variable quantities 

 of compounds containing sulphur. In these, nitrogen is 

 an invariable constituent. These are always accompanied 

 by alkaline phosphates and alkaline earths, and for both, 

 in each seed there exists a fixed and unchangeable rela- 

 tion; whenever the percentage of phosphoric acid in- 

 creases or diminishes in any seed, there is the like increase 

 or diminution in the compounds of sulphur. In the seeds 

 of cereals and in those of leguminous plants, two of these 

 compounds exist, and a third in the juices of all plants, 



