LIME 



127 



I.I 



ME 



133. How to Tell the Need of Lime. One of the most 

 common indications of the need of lime is the failure of 

 red clover on soils where it once grew. This is generally 

 due to the exhaustion of lime. If red clover fails and 

 red-top thrives we should certainly make a test of 

 lime. Clover sometimes fails because of the root-borer, 

 but, in this case, it does not fail until it has produced the 

 first crop of hay. In some regions it fails because of disease 

 (anthracnose), but, in this case, it makes a good growth 

 until the disease attacks it. If clover and alfalfa produce 

 good crops, lime will not be needed. An easy test for the 

 need of lime is to lay off a plot 



four rods square in the field. 

 Apply a bushel of lime on half of 

 the plot and apply manure on 

 half of it in the other direction. 

 We then have lime and manure 

 alone and together as compared 

 with no treatment. The lime is 

 likely to have a greater effect 

 the second year. 



134. Forms of Lime. Lime 



occurs in the earth as limestone rock or calcium carbonate 

 (CaCO 3 ). When this is burned, carbon dioxid (CO 2 ) is 

 irivcn off and we have left quicklime (CaO). This is the 

 lime that is used in plastering. When this lime is water- 

 slaked to form plaster, it takes up water and we have 

 calcium hydrate, waterslaked lime, or hydrated lime ^Ca 

 (OH) 2 ). When this is put on the walls as plaster it dries 

 out and becomes white. As it loses water, it takes up car- 

 bon dioxid from the air and the calcium carbonate is 



Fio. 54. Experiment to deter- 

 mine whether lime is needed 



