44 



immediately soluble in the soil moisture, and ready for 

 absorption by the roots. Such a mixture is known in 

 commerce as super-phosphate, and is quite easily made by 

 the cultivator himself on the small scale, provided that he 

 has some knowledge of the corrosive nature of the acid he 

 is employing. The mixture dries in a few days, and if the 

 acid has not been used in excess, it may be safely preserved 

 in gunny-bags until required. Owing to the solubility of 

 its phosphatic portion, it will always be best used, at least 

 in orchards, as a top-dressing only. It must be remembered 

 too that half its bulk consists of sulphate of lime or gyp- 

 sum formed in the decomposition of the bones by the acid. 

 This of itself is a valuable manurial ingredient. It is the 

 form in which plants most readily take up the lime and the 

 trace of sulphur they require, and its effect upon any iiv 

 jurious soda carbonate, causing brackness in the soil is 

 immediate and effective. Thomas' slag comes into the 

 cultivator's hands in a very fine powder, and the phosphatic 

 lime it contains is much more readily broken up by the 

 action of the carbonic acid in the soil than is the case with 

 ground bones. On an average it is found to contain from 

 06 to 41 per cent, of phosphate of lime, and therefore it 

 compares favourably with the medium class of superphos- 

 phates which contain from 26 to 28 per cent, and with 

 pure dissolved bones containing 20 per cent, soluble 

 phosphate and 10 per cent, insoluble matter. 



49. Confining our attention to the use of phosphates in 

 oichards only, it would appear that Thomas' slag has a 

 distinct advantage over other sources. It gives out the 

 element required, slowly, yet with sufficient readiness. It 

 does not throw all its content of phosphoric acid into the 

 soil the first season ; hence what may be termed its staying 

 power has a distinct and great advantage. The man who 

 applies bone-meal, hoping to secure this same staying power 

 for a number of years, most certainly gets it, but unfor- 

 tunately the amount of phosphoric oxide liberated per 

 season by his bone-meal is excessively small. In fact, for 

 a phosphatic manure it does not work quick enough. The 

 sum of the whole matter may be put thus : superphosphates 

 work too quickly, plain ground bones work far too slowly. 

 Thomas 7 slag strikes a medium between the two. 



