15 



make it quick enough in its action. To improve it in this respect a method 

 was introduced whereby the most of the insoluble tri-calcic phosphate of bone was 

 converted into soluble mono-calcic phosphate. This was accomplished by treat- 

 ment with sulphuric acid and the product became known as superphosphate or 

 acid phosphate. Gradually the cheaper rock phosphate has replaced the bone 

 meal in the preparation of the acid phosphate, until to-day comparatively little 

 of the bone meal is being used for this purpose. The bone in the finely ground 

 condition is really too valuable applied direct to be used in this way, especially 

 as the tri-calcic phosphate of the rock material treated with the sulphuric acid 

 forms just as available a form of plant food as would be got from the bones. Most 

 of the superphosphates on the market contain about 14 to 16 per cent, available 

 phosphoric acid. The chief advantage of this m'aterial over the undissolved forms 

 is that the phosphoric acid is quickly available. Basic slag cannot be used for 

 this purpose because it contains a large amount of iron, and under the treatment 

 with sulphuric acid phosphoric acid would be converted into the iron phosphate, 

 which would be much more insoluble than in the form in which it was originally 

 held. The ground bone and basic slag are not quick enough in their action to fully 

 roieet the needs of quick growing crops, but may be used with such crops as grow 

 through long periods, as meadows, orchards, vineyards, etc. The rock phosphate 

 will be still slower in its action, and should be applied to soils that are fairly 

 rich in organic matter, because under these conditions the phosphoric acid may 

 be brought into solution by the acids which are formed in the decay of the 

 organic matter. Basic slag should also be applied to soils rich in organic matter, 

 or even to those which have a tendency towards sourness, as it contains a con- 

 siderable amount of lime. 



Superphosphate, on the other hand, should never be applied to soils that are 

 inclined to be sour, because it is of an acid nature. The chief advantage of the 

 superphosphate over the other forms is that it contains soluble phosphate which 

 dissolves on being placed in the soil, and is thus more evenly distributed through 

 the ground than can be done by mechanical distribution. In a longer or shorter 

 time it is reverted to the insoluble form in which it was originally, but in the 

 meantime it has become so distributed through the ground that the roots can come 

 more in contact with it and it is better absorbed. 



POTASH MANUEES. 



Until the discovery of tlie potash mines in Germany in 1860, wood ashes 

 were the chief source of this constituent as a fertilizer. To-day, practically all 

 potash salts used in the world comes from the famous mines in Germany. It 

 is placed on the market in a variety of forms, but the chief materials that reach 

 this country are kainite, muriate of potash and sulphate of potash. 



The Jcainite is a crude salt containing about 12.5 per cent, of actual potash, 

 which is largely in the form of the sulphate. Along with it, however, there are 

 large quantities of ordinary salt and small percentages of chloride and sulphate 

 of magnesium. Freight rates make it almost prohibitive to bring this product 

 inland. 



