184 



made more soluble and hence quicker in its action. The actual 

 composition of superphosphate varies with the material of which 

 it is made, and ranges from 35 to 40 per cent, down to 20 per cent, 

 phosphates rendered soluble. In this state, owing to its diffusi- 

 bility, superphosphate is able to permeate through a greater quantity 

 of soil, and penetrates further than other merely mechanically- 

 divided phosphates, and thus more readily taken up and assimi- 

 lated by crops. A good dressing consists of 2 to 4cwt. per acre ; 

 or, in conjunction with farm-yard manure, 2cwt. 



Fermented Bones can readily be prepared on the farm by 

 mixing with bones J their weight of earth or burying them in the 

 manure heap, moistening them with water, urine, or liquid manure, 

 and covering the whole heap with earth. After a time, depending 

 on the temperature, the bones enter into fermentation, and 

 crumble to powder when they are dug out and used. Fermented 

 bones act more rapidly than raw bones, and can be compared in 

 their action to bone superphosphate. 



The relation of phosphoric acid (P 2 O 5 ) to phosphate of lime 

 (Ca 3 P 2 O 8 ), such as is expressed in soil or manure analysis, is as 142 

 is to 310 or a fraction less than half. Thus bonedust containing 

 50 per cent, of phosphate of lime contains somewhat less than half 

 this amount of phosphoric acid, or, in exact figures, 22'58 per cent. 



Potassium is the constituent of a fertile soil or of fertilisers 

 which ranks third in costliness. It does not occur as such, but as 

 combinations, such as chloride (muriate), sulphate, carbonate, 

 nitrate, silicate, etc. 



Potash is also known as potassium oxide (K 2 0), and as such is 

 reckoned when valuing fertilisers. 



In manures it occurs as sulphate and as muriate (chloride of 

 potassium), the sulphate form being a little more costly than the 

 muriate. 



The chief sources of potash are 



Wood Ashes, which constituted for a long time the chief source 

 of supply of potash used for agricultural purposes. The incombus- 

 tible part of " ash " of farm crops and timber contains from one- 

 fourth to one-third its weight of potash. For this reason newly 

 cleaned land, well timbered, on which the wood has been burnt off 

 the ground, will have an ample supply of potash to supply the 

 requirements of the crops for some seasons, at all events. 



Kainit is, on account of its low price in Europe, in great favour 

 as a cheap form of potassic fertiliser. Owing to its great bulk, 

 however, the price in Australia is- about double what it is in Eng- 

 land. It is chiefly extracted from salt mines in Germany, and was 

 originally deposited from sea water, and is associated with salt, 

 gypsum, and other saline substances. The crude kainit found in 

 commerce contains 12 to 13 per cent, of potash (equivalent to about 

 25 per cent, sulphate of potash), 27 to 30 per cent, of magnesia 

 salts of little or no use as a manure, and 30 per cent, of common 



