202 



The Need fo^ Lime and How to ^Ieet it. 



[JrNE. 



but arising from the fact that magnesian lime always takes 

 longer to slake and revert to carbonate than a straight calcium 

 lime, and sometimes takes so long that the soil remains 

 partially sterile for months after it is applied. This "burning " 

 effect is particularly noticeable on light soils. 



^Yhen therefore dolomitic limestone is under consideration, 

 our conclusions will be very largely dependent upon whether 

 the stone is to be ground or burnt; if the former, we shall 

 probably decide to use it, making a mental note that we would 

 rather it had been straight calcium limestone, but if lime is 

 to be made from it then we shall proceed w^ith the utmost 

 caution, getting a few tons burnt in a clamp or a neighbouring 

 lime kiln as an experiment, and testing the lime before 

 embarking on kiln building and quarry plant. 



Before leaving this thornv question of the magnesia content 

 of the stone, there is one other point on which much misunder- 

 standing exists, which it may be useful to discuss. The 

 calcium carbonate content of a Dolomite is frequently spoken of 

 as though that alone could have an agricultural value; this is 

 quite erroneous, for the magnesium carbonate is also capable 

 of neutralising soil acidity, and from this point of view a stone 

 analysing 59 per cent, of calcium carbonate (CaC03) and 

 39 per cent, of magnesium carbonate (^MgCOg) is not a 59 per 

 cent, limestone but a 98 per cent., neglecting its somewhat 

 slower action, and the possible toxic effect on certain soils. 



Another impurity frequently met with in limestone is com- 

 bined silica, which can have no toxic effect, but in both the 

 ground and the burnt stone it is not only an adulterant but 

 withdraws an equivalent amount of the calcium present from 

 taking an effective part in soil neutralisation. Other impurities 

 likely to be met with are iron, uncombined silica, and organic 

 and earthy matters, none of which need be considered as they 

 are only diluents, and usually occur in quantities too small to 

 be of much importance. 



Method of Utilisation. — Having found and analysed the stone 

 we must decide whether it will be better to reduce it to powder 

 in a mill, or to burn it toquick-hme in a kiln. If the limestone con- 

 tains a high percentage of calcium and the distance over which 

 it will have to be drawn is great, and providing there is an 

 ample supply of coal and wood readily available, then burning 

 the stone is clearly the right thing ; on the other hand a Dolomite 

 is usually better applied to the soil as ground stone. Between 

 these extremes there are a great number of intermediate cases 

 which must be decided on their merits. 



