MECHANICAL PREPARATION OF SOILS. 



47 



integrating influence of the atmosphere. Oxygen enters into combination with 

 all soils ; and it can be demonstrated that about one-half of the materials of 

 the globe's crust, including its animal and vegetable pi'oducts, is composed of 

 ox3'gen. The chemist can only obtain it as a gas ; but when combined, it 

 assumes divers forms, and occurs as liquids and solids, as well as a gas. About 

 a half by weight of flint, rock-crystal, and other forms of silica, is oxj'gen ; 

 about a third of alumina, or pure clay, by measure, and a fifth of the atmo- 

 sphere by weight, are oxygen ; and no plant or animal can exist without 

 oxygen entering largely into its constitution. 



123. '^Lirnc, employed as a manure," to quote Dr. Scoffcrn's "Handy- 

 Book," ''performs three well-marked functions at least, perhaps more : in all 

 it is a powerful ameliorator of soils, and under two series of conditions it 

 should be used in different fonns. New-burned caustic lime is a powerfully 

 corrosive body ; when brought into contact with animal and vegetable 

 tissues, it rapidly disorganizes them. Even if the tissues be living, still the 

 quicklime will effect their disorganization. Hence arise the following deduc- 

 tions. When we have to deal with a rank new soil, teeming with noxious 

 weeds, and with seeds ready to spring into life on the first opportunit}'-, or 

 when the object is to convert hai'd animal tissues, such as horn or kelp, or even 

 softer ones, as clippings of woollen cloth, into a useful manure, unslaked 

 lime is employed. On the other hand, when the object in adding lime to 

 the soil is to supply the calcareous element as a mechanical means of ame- 

 liorating the texture of the soil, and a physiological means of supplying food 

 to certain crops, and where there are no weeds nor noxious germs to destro}^, 

 nor organic tissues to decompose, then the employment of lime should be 

 in the mild or slaked state." In both its forms, therefore, lime is a powerful 

 agent in the improvement of soils, especially those in which clay and peat exist 

 to any extent. 



