1505.] 



The Use of Lime. 



401 



good quality, should contain 90 per cent, or over of carbonate 

 of lime (CaC0 3 ), which is simply lime in combination with 

 carbonic acid. The burning in the limekiln drives off the 

 carbonic acid as gas into the air. From 1 ton of pure lime- 

 stone n£ cwt. of burnt lime are produced, while 8f cwt. of 

 carbonic acid gas pass off into the air. 



The burnt lime thus obtained from the lime-kiln greedily 

 absorbs and combines with water, and readily unites again 

 with the small amount of carbonic acid gas present in the air. 

 It should, therefore, be as little exposed to rain and to the air 

 as possible, and applied to the land without undue delay. 



Where coal is cheap the price of good lime at the lime-kiln 

 is probably on the average about 9s. a ton. It is usually bought 

 by the farmer at so much a ton at his nearest station, including 

 the cost of railway carriage. 



In purchasing lime the main point is to have a guarantee of 

 the percentage of pure lime (CaO), not carbonate of lime. It 

 should be possible from our best limestone quarries to obtain 

 lime guaranteed to be of not less than 85 per cent, purity, and 

 actually better than this. It is also desirable that there should be 

 a guarantee that not more than 4 per cent, of magnesia is con- 

 tained in the lime, as there seems to be undoubted evidence that 

 an excess of this substance is distinctly harmful to crops. There 

 must also be no appreciable amount of unburnt limestone or 

 chalk left in the lime. 



Methods of Application. — Probably the most common method 

 of applying lime to the soil is to put it on the land in little 

 heaps, and there to allow it to slake naturally, or to add a small 

 amount of water from a water-cart and then to cover up with 

 soil. In a short time the lime will become slaked, and may be 

 spread with a spade or shovel, after which it should be harrowed 

 into the soil as soon as possible, as lime is much more effective 

 when it is covered by the soil immediately it has been spread. 

 The best method of application, however, is to slake the lime 

 into a fine powder, as is done by a mason's labourer, before 

 applying it to the soil. In doing so the lime shells are spread 

 in layers about a foot deep, one above the other, in a sheltered 

 position, each layer being slaked with water at the rate of rather 

 under 6 cwt. per ton of lime when the latter is good, and less 



K K 



