(3) Ground Ihnestone. Raw limestone first ground very fine is 

 now offered by some dealers, and is reconunend in certain quarters. 

 In deciding whether to use this form of lime, the following points 

 should be remembered : 



(a) Limestone is a carbonate of lime and it will require about 

 175 pounds of this compound to furnish as much actual lime as will 

 be contained in 100 pounds of burned lime. 



(b) Limestone however finely ground is soluble only to a small 

 extent and its action will be far slower in most soils than that of 

 freshly slaked burned lime. 



(4) Agricultural lime. Some companies are now putting on the 

 market special preparations of lime which are recommended as 

 especially fitted for use in agriculture. These are usually in a very 

 fine mechanical condition and are in most cases made up in part of 

 fine ground carbonate of lime and in part of slaked lime. The 

 package in which these are offered makes them exceedingly conven- 

 ient for handling and for application, but pound for pound such 

 grades of lime are less effective than equal amounts of burned lime. 



(5) Marl. Marl is a deposit consisting of variable proportions 

 of carbonate of lime (coming from disintegrated shells) and fine 

 earth. When applied to soils in suitable quantities, it is likely to 

 produce much the same effects as will be obtained from an applica- 

 tion of air slaked lime. It is not, however, so rich in actual lime as 

 the latter, and it will require more than one pound of marl to pro- 

 duce the effects likely to be produced by application of that amount 

 of air slaked lime. Statements of the average composition of marl 

 can have no particular value. In order to determine whether it is 

 better economy to use marl or some other form of lime, it will be 

 necessary to know its composition. Efficiency will be measured, in 

 large degree at least, by the relative proportions of actual lime. 



(6) Land plaster. Land plaster, if pure, is made up of finely 

 ground sulfate of lime (gypsum) which contains only about 40 

 pounds of actual lime in 100. It is less energetic in its action on 

 most soil constituents than lime in other forms. It is, however, 

 often beneficial and may serve numerous useful purposes which will 

 not be discussed here. At prevailing prices it is not, however, 

 usually advisable to select plaster as the material to be used for the 

 correction of the faults most common in soils needing liming. 



A 



