6o4 Journal oj Agriculture, Victoria. [lo Oct., 1912. 



therefore, 100 lbs. of calcium carbonate yield.s 56 lbs. of calcium oxide, 

 which remains as a solid, and 44 lbs. of carbonic acid, which is driven' 

 off as a gas. 



2nd — 



Calcium Oxide Water Calcium Hydrate 



CaO + H/J = CaH.O, 



This change is brought about b\ wetting the (calcium oxide CaO> 

 lime; the molecular weight of each substance being — 



CaO + Water = CaH.,0.^ 



56 + 18 ^ 74 



56 lbs. of calcium oxide and 18 lbs. of water yield 74 lbs. of calcium 

 hydrate. 

 3rd— 



Calcium Hydrate + Carbonic Acid = Calcium Carbonate + Water 

 CaHoO, + CO., = CaCOg + H,0 



This change is brought about bv the carbonic acid of the air and soil ;. 

 the molecular weight of each substance being — 



CaH.p., H- CO., = CaCO, + H.^O 



74 + 44 = 100 + iH 



therefore, 74 lbs. of calcium hydrate and 44 lbs. of carbonic acid yield 

 100 lbs. of calcium carbonate, and 18 lbs. of water. This was the 

 quantity of water combined with the calcium oxide to form calcium 

 hydrate, so the cycle is completed. 



From the above results it is evident that heat applied to calcium car- 

 }x>nate alters its composition with reduction, of weight ; that the residue 

 of lime left combines first with water to form calcium hydrate, and this 

 calcium hydrate, if left exposed to the atmosphere, reverts back again 

 to calcium carbonate, with no actual loss. 



There is another important compound of lime which lies outside of 

 the cycle given above, viz., the bi-carbonate of calcium CaHo (COg)^, 

 formed by the addition of one part of water, and one part of carbonic 

 acid gas to the ordinary carbonate, thus CaCO;, + H.^0 + CO2 = CaH._, 

 (COg).^. It is through this form of lime compound that the chief losses 

 of lime from the soil occur. Unlike the single carbonate of lime (chalk, 

 limestone, &c.) this double carbonate is .soluble in water, and when it is 

 formed by the carbonic acid dissolved in the soil water coming in contact 

 with particles of calcium carbonate, the latter is dissolved and pas.ses 

 away, or leaches out of the .soil by means of drainage or in gravitational 

 water. 



Lime Proper or " Burnt T.ime." 



Lime (calcium oxide CaO) is always made commercially by taking 

 advantage of the action of heat on limestone or other form of calcium 

 carbonate. The general procedure adopted consists in burning the natural 

 deposit in a specially constructed kiln, into which carbonate of lime and 

 fuel are added in alternate layers from the top until the kiln is filled. 

 The fuel is then ignited, and the process of burning can be kept on 



