360 CHEMISTRY. 



These two parts can be obtained separate from each other 

 by processes which are described in the first chapter of 

 Hooker's "First Book in Physiology." The gelatin is of 

 great value as a fertilizer for any crop because of the nitro- 

 gen which it contains ; and the phosphate of lime is espe- 

 cially favorable to the development of seeds, and therefore 

 bone-dust is peculiarly appropriate as a manure for grain- 

 fields. It is on account of this phosphate of lime that bone- 

 dust is so beneficial to dairy lands. Milk and cheese both 

 contain this substance. There is about half a pound of it 

 in ten gallons of milk. Bone-dust is also an excellent ma- 

 nure for wheat; for though this is a silica plant ( 483), 

 the presence of phosphates in the soil is essential to the 

 formation of the seeds. If the soil be rich in silicates but 

 deficient in phosphates, excellent straw will be obtained, 

 but the grain will be small in amount : it will be a crop 

 better calculated to make bonnets than bread. It is calcu- 

 lated that 1 cwt. of bone-dust is equal to 25 or 30 cwt. of 

 stable-manure. Although bones contain such fertilizing 

 materials, they must be well pulverized in order that they 

 may be immediately available for the nutrition of plants. 

 It often takes even twenty or more years for the soil to 

 disintegrate fragments of bone of the size of a hazel-nut 

 or a pea, and yet such fragments arc frequently seen in the 

 bone-dust of commerce. 



503. Lime. While guano, bone-dust, stable-manure, etc., 

 act as direct nutrients, giving actual substance to the plant, 

 the action of lime is for the most part indirect. It acts in 

 many ways. In some cases its chief effect upon the soil is 

 mechanical, rendering it loose and porous. In other cases, 

 as stated in 496, it neutralizes the acidity of the soil, and 

 thus makes it fertile. In still other cases it excites a more 

 rapid decay of the humus, and thus provides more nutri- 

 tious matter in the soil for the plants. And still again it 



