628 Circular No. 7. 



Equivalent 

 in composition 

 Calcium in to loo lbs. 



100 lbs. lump lime. 



(a.) CaO, Lump lime, freshly burned lime, 



quick lime 71 100 



(b.) Ca(OH)2 — Hydrated lime, water- 

 slaked lime 54 132 



(c.) CaCOa — Lime carbonates, air-slaked 



lime, ground limestone, marl 40 180 



(d.) CaS04-|-2H20 — Gypsum, land plaster 23 310 



(e.) Ca3(P04)2 Lime phosphate, ground 38 Pure 187 



phosphate rock 39 25;?^CaC03 181 



(f) CaH,(POJo+CaS04— Acid phos- 

 phate (15^'' P2O..,) .... 23 310 



(g.) (CaO)4P205 Basic slag, Thomas 



phosphate powder 43 165 



(h.) Ashes (containing quick lime) 15 to 30 450 



Strictly speaking, the lime manufacturers are concerned with only 

 the first three forms but these must compete to some extent with other 

 forms. Phosphate fertilizers may sometimes owe their benefits to their 

 lime contents. The same result might then be obtained from lime at 

 a much less cost. 



Tn general, we would avoid the use of any form of lime contain- 

 ing sulfate, owing to its tendency to develop an acid condition. 

 Sulfate fertilizers have been shown not only to increase the loss of 

 lime but to increase the soil acidity. Ammonium sulfate fertilizers are 

 particularly obnoxious in this way, as shown by the Pennsylvania, 

 Rhode Island and other results. The elimination of sulfate cuts out 

 gypsum and, as a source of lime, should exclude acid phosphate. The 

 other forms are to be considered on the basis of their availability, cost 

 of calcium, and supplementary material carried. 



2. The actual amount of calcium carried is clear, from the above 

 table. This must partly afifect the cost and will determine transporta- 

 tion and handling charges. 



3. Availahility of lime is closely related to the composition, (a.) 

 Chemically, the quick lime is most active, and on that point there is 

 no distinction between lump lime and hydrated lime, since in a moist 

 soil they must reach the same condition. All of the functions of lime 

 are most efifectively executed by this form. It passes into solution 

 readily. Consequently, it is generally considered that precautions 

 must be exercised in the amount applied. It has been considered to 

 destroy organic matter too rapidly. Whether there is a chemical effect 

 distinct from the biological effect is not clear. At any rate, it does 



