THE CHEMISTRY OF THE SOIL. 89 



There arc few soils which will not derive benefit from the application of lime, 

 even when this substance is present in fair proportion. A. I >. Hall, the late 

 Director of the Rothamsted Station, states that Knglish experience shows thai 

 soils containing less than 1 per cent, carbonate of lime require liming. This 



represents aboul .', per cent, lime, and there are not a great number of soils 

 in New South Wales which contain as much as this, whereas the hulk of our 

 soils contain considerably less. Liming is beneficial on a great variety of 

 soils, and is to be regarded rather as a means of improving the land "than as 



a direct plant -f 1. The soils on which it is particularly beneficial are the 



following : — 



1. Soils deficient in lime. 



2. Sour soils, on which it acts as a sweetening agent, neutralising the 



soil-acidity. On land which is newly opened up, or land which is 

 being reclaimed from swamps, the addition of lime is an essential. 



3. On stiff clay soils. The action of lime on this class of soils is to 



lighten them and render them more friable and amenable to tillage 

 operations. 



4. On sandy soils, lime acts in an opposite manner, as will be shortly 



explained, consolidating them and increasing the cohesive and 

 capillary power of the soil. 



5. On land which is destined for leguminous crops, or such crops as are 



specially benefited by the presence of lime, such as sugar-cane, 

 maize, &c. Where a green crop is sown to be ploughed under 

 (green-manuring) the previous application of lime to the soil is of 

 the greatest benefit in promoting the growth of the green crop. 



Nature of Lime. 



Burnt-lime, stone-lime, or quicklime is obtained by burning limestone 

 (carbonate of lime) in kilns of special construction. In the process of burning 

 or calcining, carbonic acid and water are driven off, and the burnt product is 

 pure lime (calcium oxide) of greater or less purity according to the purity of 

 the original stone. Other substances, having the same composition as lime- 

 stone, also yield lime on being burnt, such as chalk, marble, shells, ifcc. If 

 the lime has been properly burnt it forms a very hard, stony substance, nearly 

 white, which slakes, or combines with water, with great avidity, crumbling 

 to a fine white powder, and evolving sufficient heat to convert a part of the 

 water into steam. In slaking, it combines with the water, slaked lime being a 

 hydrate of lime. As its function in the soil is principally mechanical, a test of 

 its goodness lies in the readiness and completeness with which it slakes. Both 

 under-burnt and over-burnt lime slake badly, though from different causes. 



Burning Limestone on a Small Scale. 



If only small quantities are to be burnt at a time, the use of a kiln may 

 be dispensed with and the lime burnt in the open or in an excavation on the 

 side of a hill. This is best done by placing the wood and limestone in 

 alternate layers. About 1 ton of wood is required to 2 tons limestone. 



A method reported as successful by the General Manager of the State 

 Brick and Lime Works is as follows :— He excavates about 10 feet into a 

 bank, thus making the sides of the excavation act as the three sides of a kiln, 

 and then lays about 18 inches of timber on the bottom; then 18 inches 

 limestone on the top of this, filling up the excavation with alternate layers 

 of wood and limestone ; he then lights the timber at the bottom, and the 

 fire burns through the lot. The lime produced is quite good enough for 

 agricultural purposes. 



