IRISH GARDENING. 



January 



Lime. 



Bv M. J. Jamison, Associate of the Royal College 

 of Science for Ireland. 



LI M E (calcium oxide) is obtained by burning 

 limestone (calcium carbonate). The heat 

 produced by coal, turf, &c., drives off 

 the carbonic acid gas (CO2), leaving behind 

 CaO, ash, and other impurities. The percent- 

 age of lime (CaO) depends on the quality of 

 the rock used for burning. Some limestones 

 contain 98 per cent, of the carbonate, whilst 

 " clayey" limestones contain about 68 per cent. 

 Again, some limestones contain much magnesium 

 carbonate brought about by the replacement of 

 the lime by magnesium. When lime contains 

 4 per cent, of magnesium (MgO) or over it is 

 considered as harmful to plant life as it is slow- 

 in taking up CO2. A pure limestone contains 

 in every 100 parts bj- weight 56 parts of lime 

 and 44 of carbonic acid gas. Lime is of a 

 caustic nature, and combines readily with water, 

 forming slaked lime Ca (OH2), which is slightly 

 less caustic. When much water is added to 

 slaked lime, milk of lime is produced. Since 

 lime is soluble to a small extent in water, if 

 milk of lime is allowed to settle a clear liquid re- 

 mains on the top, termed "lime water." By 

 blowing one's breath into lime water the car- 

 bonate is precipitated owing to the lime taking up 

 carbonic acid gas. The causticity of lime, both 

 unslaked and slaked, enables them to burn up 

 organic matter in the soil, setting free ammonia 

 from nitrogenous compounds, and also to act 

 as disinfectants. Their alkalinit\- enables them 

 to neutralise acids in the soil, making it more 

 suitable for bacterial and plant life, besides 

 sweetening the herbage. By their physical 

 action sandy soils are made more compact, 

 heavy clay soils are opened up by changing 

 them from a " one-grain " state to larger 

 aggregates, thus making the drainage better, 

 allowing air to pass through, and finally render- 

 ing them more easy of cultivation. If a stiff 

 soil is allowed to settle under water-logged 

 conditions, there comes a time when the grains 

 are so packed together that no water percolates 

 through ; but if lime water is added, water begins 

 again to flow owing to the aggregation of the 

 grains to form larger particles. Lime sets free 

 potash from combinations in the soil, and also 

 when absorbed, or rather absorbed by the soil — 

 that is, if we add a potash solution to a soil. 



and after a time wash all the potash possible 

 out of it, then, by adding lime in solution, 

 pota.sh will again appear in the filtrate. We 

 must not, however, consider this as a chemical 

 replacement, but rather a physical effect, caused 

 by the absorptive capacity of the soil grains 

 for certain substances in solution. 



When lime is applied to the soil it is some- 

 times left in small heaps and allowed to absorb 

 moisture from the air to slake it, but the 

 more common practice is to throw water on 

 successive lajers and shovel into a heap. Too 

 much water renders the mass pasty and difficult 

 to spread. The slaked lime is spread on the 

 land at the rates of from one to two tons per 

 acre, and harrowed in. Owing to its slight 

 solubilit}- part maj' become washed out of the 

 soil during hea\'y rains. However, in dilute 

 solutions the soil can absorb 94 per cent, of the 

 lime, but if the solution is made twenty times 

 stronger 54 per cent, only is absorbed. Of late 

 jears much of the burnt lime has been ground, 

 and is sold under the name of " ground lime." 

 In this state it is easily spread b\- machinery, and 

 is more caustic in its action than slaked lime. 

 The cost of grinding is about 6s. per ton and 

 of bagging 3s. The bags generally burst 

 owing to the slaking of the lime, and become 

 of no value. Ground lime should be bought 

 under a guarantee of at least 85 per cent, of 

 CaO. Many samples only contain 50 per cent., 

 whilst as much as 22 per cent, of magnesium 

 ma)' be found. Often unburnt limestone is 

 ground owing to defective burning. This is by 

 no means harmful to the land, but it is not 

 economical, as 56 cwts. of burnt lime contains 

 as much lime as 5 tons of the unburnt, pure 

 sample. So far ground lime is expensive, but 5 

 to 6 cwts. per acre is considered a fair dressing 

 every year. 



Gas lime is often applied to land. When 

 fresh it contains 28 to 40 per cent, of water, 

 and on an average 34 per cent, equivalent of 

 CaO, very little of which is in a caustic state. 

 It is applied at the rate of two to four tons per 

 acre. The lime, having been previously used as 

 a purifier for coal gas, contains many sulphur 

 compounds, some of which are injurious to plant 

 life. However, when gas lime has been exposed 

 to the air for a few months these are oxidised 

 and rendered harmless. 



Chalk is a soft limestone, and is applied to 

 the surface of the soil, thus exposing it to rains 



