9 



intimately mixed with the soil, thus requiring a smaller applica- 

 tion per acre than would be the case with a coarse limestone. 



Marl. — Marls are geologically confined to the Alluvial and Ter- 

 tiary strata. The composition of pure marls is quite similar to 

 limestone, the lime being present in the form of carbonate. They 

 differ in appearance from limestone in having an amorphous or 

 non-crystalline structure. In some of the Southern states more 

 or less phosphoric acid is found associated with marl deposits. 

 This very likely is due to the bones of small animals being de- 

 posited with the shells, which are in reality the source of marls. 

 There are hardly any two marl deposits which have the same 

 chemical composition — they contain varying quantities of earthy 

 matter and should always be purchased upon a guaranteed analy- 

 sis of calcium oxide. A deposit of considerable extent has been 

 discovered in the vicinity of Barton, Vermont. It appears to be 

 of good quality and should be a valuable source of lime provided 

 it can be secured so that 100 pounds of calcium oxide compare 

 favorably in cost with an equal amount in other lime products. 

 Dried marls are usually in a suitable mechanical condition for 

 direct application, and if of satisfactory quality, they are efficient 

 sources of lime. 



Quick or Burned Lime. — Chemically speaking, this material 

 is calcium oxide (CaO). It is known also as caustic or unslaked 

 lime. It is made by heating to a red heat in kilns either lime 

 rock or oyster shells. Kilns are constructed so that wood, coal 

 or gas can be used as a fuel. The heating process drives off the 

 carbonic acid (CO2) and the quicklime (CaO) results. This 

 material is the most active form of lime and is not ordinarily 

 used on the land. It will absorb moisture from the atmosphere 

 and thus increase largely in volume. It cannot, therefore, be 

 readily shipped in bags, and those who have used it in the ground 

 fonn complain that the fine dust, settling upon the perspiring 

 men and horses, causes serious burning and discomfort. Caustic 

 lime can, of course, be bought in barrels or in bulk in lump form, 

 so that 100 pounds of calcium oxide will cost less than when slaked 

 or hydrated, or in the form of carbonate. One hundred pounds 

 of quicklime contains as much calcium oxide as 178 1-2 pounds 

 of carbonate of lime (ground limestone and marl), or 132 pounds 

 of slaked or hydrated lime Ca(0H)2. 



Slaking Lime. Some advocate placing the Itmip lime in small 

 heaps, covering with soil and allowing to slake gradually. 



If a machine is available for spreading the lime it should pref- 

 erably be slaked in heaps of moderate size by the gradual addi- 

 tion of water, using care not to apply enough to render the lime 

 pasty or wet. The proportion of about two pailfuls of water to 

 each 100 pounds of lime, if so applied as to wet all the lumps as 



