186 Journal of Agriculture, Victoria. [11 March, 1918, 



Steer's limestone quarry, at "Warniambool, illustrated in Plate 156, 

 represents a good type of limestone deposit. 



Great diversity of opinion, as to the quantity of lime per acre wliieh 

 would constitute a fair dressing, exists among orchardists, and the quan- 

 tities of fresh slaked lime, which is the form most commonly used, range 

 from 10 cwt. to 2 tons per acre. In determining the suitable amount of 

 lime for an application the orchardist should be influenced chiefly by the 

 state of the soil as regards its acidity, its general physical condition, and 

 manurial wants, as well as its condition regarding drainage. The soil 

 should not be allowed to become wholly depleted of lime before being 

 rej)lenished with this ingredient. It is generally recognised now that 

 better results attend frequent light dressings of lime than accrue from 

 heavy ones applied at long intervals. 



Pkoducing Slaked Lime. 



Slaked lime is the form most commonly used as a manure by the 

 orchardists. It is obtained when the limestone or calcium carbonate 

 taken from the quarry is submitted to a red heat by being burned in a 

 kiln until the Avhole of the carbonic acid content of the stone is driven 

 off in the form of gas. What remains of the limestone after the gas has 

 all burned out is known as quicklime or calcium oxide. On water being 

 poured on the quicklime a chemical combina-tion takes place, resulting 

 in the formation of slaked lime or calcium hydrate. 



The following has been taken from an article on " The Chemistry 

 of Lime," by P. Rankin Scott, Chemist for Agriculture, published in 

 this Journal, October, 1912 : — 



In actual practice there are three distinct forms of lime com- 

 pounds applied to the soil, namely : — 



Calcium oxide (CaO) lime. 

 Calcium hydrate (CaHoOo) slaked lime. 

 Calcium carbonate (CaCOy) chalk, limestone, shell, kc. 

 What these forms are and the relation they bear one to the other 

 can be seen by means of the lime cycle : — 

 Calcium Carbonate 

 CaCO, 

 Limestone, <S:c. 

 Calcium Hydrate Calcium Oxide 



CaH^Oo CaO 



Slaked lime. Lime. 



The above cycle illustrates the changes of one form into the other. 



In connexion with the relative value of the different forms of lime 

 and desirable standards, Mr. Scott further writes: — 



56 lbs. of fresh burnt lime contains the same amount of lime as — 

 56 lbs. of fresh ground lime. 

 74 lbs. of water-slaked lime. 

 100 lbs. of carbonate of lime (as a powder — ground lime- 

 stone, chalk, (Src). 

 100 lbs. of old air-slaked lime. 

 172 lbs. of sulphate of lime (as gypsum). 



