The Science of the Soil 93 



The result is then known as hydrate of lime. When quicklime is exposed 

 for a time to the air, it gradually absorbs carbonic acid gas, and thus 

 reverts to a chalky or carbonate of lime condition. 



Chalk or limestone (calcium carbonate) is known to geologists as organic 

 rock, because it is made up of the remains of shells and bones of sea and 

 freshwater fish. This may be seen by rubbing down some fragments in 

 water and examining the dried sediment under the microscope. Minute 

 shells, pieces of coral and sponges, and broken fragments of shells will be 

 observed, as well as the remains of other marine creatures. Limestone hills 

 and rocks are to be found in many parts of the world thousands of feet 

 above sea level, and bear silent testimony to the upheavals that must have 

 taken place on the surface of the globe in past ages. In the same way our 

 coal seams represent ancient forests and fertile vegetation that have become 

 submerged, and afterwards covered with deposits of other layers of soil. 



Lime. Lime, to use the popular term, is a most important ingredient 

 in soils, and may be employed in various forms, such as marl, gypsum, 

 quicklime, chalk, slaked lime, gas lime (or " blue billy "). For a heavy, wet, 

 clayey soil a heavy dressing of quicklime is one of the ways of bringing it 

 into a good state of cultivation. In milder forms of chalk (carbonate of 

 lime) or gypsum (plaster of Paris) it is a valuable adjunct to good garden 

 soils, especially if they have been overdressed with organic manures. 



The advantages of adding lime to the soil may be summed up as 

 follows: 



1. It makes a stiff or clayey soil drier and more porous by making 

 the sticky particles coagulate or flocculate, and thus leave passages for the 

 air. This may be proved by putting a little lime into a glass of muddy 

 water. The particles that would otherwise float about for a long time soon 

 come together in flocks and drop to the bottom, leaving the water clear. 



2. Lime, being an alkali, is fatal to sourness and acidity in the soil, 

 and renders it "sweet" and favourable to vegetation. Where magnesia 

 is in excess the addition of lime will rectify any ill effects. 



3. Without the presence of lime in the soil beneficial micro-organisms 

 would not be generated from the organic constituents, and there would 

 be a lack of nitrogenous food. On the other hand, when a soil has 

 become too rich in nitrogenous foods, that cause luxuriant, sappy, and 

 unproductive growths, the addition of lime will soon restore the balance, 

 although at first giving apparently greater vigour to the shoots. 



The presence of lime in any soil may be detected in a simple way. 

 Take a fair sample and place in a glass, and pour over it some fairly 

 strong acid, such as hydrochloric. If lime is present a vigorous fizzing or 

 effervescence will take place; if not, it may be assumed that little or no 

 lime is present and it should be added. 



Peat. This name has been applied to the remains of plants that have 

 accumulated in the course of centuries on the margins of shallow lakes 

 and in marshy land. The lakes or marshes gradually disappear with 

 the encroachment of the vegetation, and the latter becomes pressed down 



