158 MANURES. 



finest bone-dust, we can understand that their action 

 as a manure would be correspondingly more rapid." 



In saying that the phosphate of lime is insoluble, 

 it is meant that it is insoluble in pure water. Water 

 which contains either carbonic acid, ammonia, or 

 common salt (and all soil water contains one or 

 more of these), has the power of dissolving it, and 

 making it available to roots. The action is slow, 

 but it is sufficient, and it is the more rapid the finer 

 the pulverization of the phosphate. The fine pre- 

 cipitated phosphate exposes much more surface to 

 the action of the water, and can consequently be 

 taken up much more rapidly. 



Super-phosphate of lime may be made from whole 

 bones, bone-dust, bone-black, or from the pure ashes 

 of bones, or from phosphatic guano. 



The reason why super-phosphate of lime is better 

 than phosphate, is therefore easily explained. The 

 phosphate is very slowly soluble in water, and conse- 

 quently furnishes food to plants slowly. A piece 

 of bone as large as a pea may lie in the soil for years 

 without being all consumed ; consequently, it will be 

 years before its value is returned, and it pays no in- 

 terest on its cost while lying there. The super-phos- 

 phate is very rapidly dissolved, and if evenly spread 

 is diffused by the water of rains throughout the soil, 

 coating its absorbent particles with a nutriment held 

 in a state of physical combination, ready to be 

 yielded to the action of roots; hence its much 

 greater value as a manure. 



It is true that the phosphate is a more lasting 



