122 



CHEMICAL FERTILIZERS 



some of the constituents, and that the citric solubility 

 increased with the lime content and decreased with the 

 magnesia content. Robertson showed the arbitrary results 

 of the citric solubility test (p. 126). Great difference of 

 opinion has been expressed as to the value of the citric 

 solubility indications ; some find that they are of great 

 value, and others find that they give results of little impor- 

 tance. As tested on the hay crop at Cockle Park, it was 

 found that the slags of medium solubility were the most 

 useful. When the results obtained from the hay crops at 

 Cockle Park are put into curves, there is an optimum point 

 in the curve, showing that the best results are obtained from 

 slags of a medium composition. The extreme types of slag 

 have not produced the best results. The only thoroughly 

 reliable estimate of the value of the slag is its percentage of 

 phosphoric acid. The fineness is undoubtedly an important 

 point, both owing to the difficulties of distribution on the 

 field, and on account of the different degree of solubility after 

 application. Experiments to test this point were made many 

 years ago at Cockle Park, in which it was found that slags 

 approaching the standard of the loo-mesh sieve produced 

 the best results, whilst those that were very coarse were 

 almost useless. A few typical analyses are given in Table 13. 

 In this table the citric soluble ingredients have been tested 



TABLE 13. 

 ANALYSIS OF BASIC SLAG. 



