Fertilizers and Feeding Stuffs, 377 



carbonate (or carbonate of lime), such as limestone, in order to 

 decompose this compound and drive off carbon dioxide. Thus, 

 calcium carbonate decomposes into calcium oxide and carbon dioxide. 

 Quicklime or burnt lime ordinarily contains, besides free calcium 

 oxide, small proportions of calcium carbonate and calcium hydrate, 

 together with the mineral impurities originally present in the lime 

 stone, as well as a certain amount of ash from the fuel employed, 



2. — Calcium Hydrate. 



The commercial form of this is known as slaked lime, and is 

 produced by adding^ the proper quantity of water to quicklime, the«e 

 two chemically combining with the generation of a considerable 

 amount of heat. Pure calcium hydrate would be a combination of 

 approximately 76 per cent, of calcium oxide and 14 per cent, of water, 

 but in ordinary slaked lime there would of course be present the 

 original impurities of the burnt lime, and a portion of the calcium 

 oxide Avould have changed to calcium carbonate. 



The above forms oi lime go under the term of caustic lime owing 

 to their alkaline nature. 



3. — CalciuTn Carbonate. 



This is commonly known as carbonate of lime, and is found in 

 nature as limestone, marble, chalk, coral, etc., but there is always a 

 certain proportion of other substances present as impurities in these 

 natural materials. In contradistinction to the caustic limes these 

 forms are termed mild jimes. Either of these natural forms of 

 carbonate of lime may be ground up finely for applying to the soil as 

 a manure, and this fine powdery product is sold nnder the name of 

 agricultural lime, but the term " lime," strictly speaking, should 

 only be applied to calcium oxide. When buying this agricultural 

 lime it is very necessary to know how pure it is, that is, the percentage 

 of calcium carbonate actually present. Pure calcium carbonate is a 

 combination of 56 per cent, of calcium oxide with 44 per cent, of carbon 

 dioxide, but no agricultural lime placed on the market is absolutely 

 pure calcium carbonate. Therefore, supposing an agricultural lime 

 is guaranteed to contain 55 per cent, of calcium oxide it is very 

 essential to know whether all that calcium oxide is present in 

 combination with carbon dioxide as calcium carbonate or not, for in 

 such a material other combinations of calcium oxide may not be of so 

 much use from a manurial point of view. 



From the above explanations it is evident that in all the above 

 forms of lime manures the essential constituent is the calcium oxide 

 that is present, either in the free state or in combination with water 

 (as hydrate), or with carbon dioxide (as carbonate). It is therefore 

 customary to value a lime manure by the amount of calcium oxide 

 present in it in any of these three forms. Lime manures do not 

 come under the scope of the Fertilizers Act, therefore it is not com- 

 pulsory on sellers to give a guaranteed analysis of such materials, but 

 when buying any of them it is advisable that such a guarantee be 

 insisted upon, for there is a very great difference ^n the composition 

 and quality of the various agricultural limes, for instance, that are 

 on the market at the present time. 



