BoxE-i»usT AND srPKi:rin>srn.\TE of i.imk. 317' 



Tin- i)li(>si)li;il(' of liino in bones is insoluble in water, Ihoiij^li 

 niin wilier conlaiiiinj; carbonic acid, and the water in soils, slowly 

 dissolve it. Hy Ireatini; the bones witii sulplinric acid, tiic phos- 

 phate of lime is decomposed and rendered soluble. ('onse(inently, 

 bone-dust treated with sulpiiurie acid will act much more rapidly 

 than ordinary l)one-dust. The sulphuric acid does not make it any 

 richer in phuspimric acid or nitroi:en. It simply renders them more 

 availalile. 



" And yet," said the Doctor, " the use of sulphuric acid for ' dis- 

 solvin;;' l»ones, or rather phosphate of lime, introduced a new era 

 in agriculture. It is the ^rand ai^ricultural fact of the nineteenth 

 century." 



"It is perhapp not necessary," said I, " to pive any direction for 

 treatin.: bones with sulphuric acid. We have got beyonil that. 

 We can now buy superphosphate cheaper tiian we can make it 

 from bones." 



" Bui IS it as good ? " asked the Deacon. 



"Soluble phosphate of lime," said I, "is soluble phosphate of 

 lime, and it makes no dilFerence whether it is made from burnt 

 bones, or from phosphatic guano, or mineral |)hosphate. That ques- 

 tion has been fully decided by tlie most satisfactory experiments." 



"BL'fore you and the Deacon tliscuss that subject," said the Doc- 

 tor, " it would be well to tell Charley wiiat supcrjjhosphate is." 



"I wish you would tell me," said Charley. 



"Well," said the Doctor," phosphate of lime, as it exists in 

 bones, is composed of tliree atoms of lime and one atom «)f phos- 

 phoric acid. Chemists call it the tricalcic phosphate. It is also 

 called the basic phosphate of lime, and not unfrequcntly the 

 'bone-earth phosphate.' It is the ordinary or common form of 

 phosphate of lime, as it exists in animals, and plants, and in the 

 various forms of mineral phosphates. 



"Then there is another pliosphate of lime, called the dicalcic 

 phosphate, or neutral phosphate of lime, or reverted phosi)hate of 

 lime. It is composed of one atom of water, two atoms of lime, 

 and one atom of pliosphoric acid. 



" Then we have wliat we call superphosphate, or acid phosphate 

 of lime, or more properly monocalcic phosphate. It is composed 

 of »wo atoms of water, one atom of lime, and one atom of phos- 

 phoric acid. This acid phosphate of lime t.« soluble in ipater. 



"The manufacture of superphosphate of lime is based on these 

 facts. The onr-Vmc phosphate is soluble, the threeWmo phosphate 

 is insoluble. To convert tlie latter into the former, all we have 

 to do is to take away two atoms of lime. 



