PHOSPHATIC MANUKES 223 



The change may be represented by the following 

 equation l : 



No great harm is likely to result from mixing small 

 quantities of these two substances if it be done in the 

 open air immediately before they are applied to the 

 land. At the worst it can only spoil the superphosphate 

 by causing it to revert to the insoluble state. The only 

 advantage of mixing the manures is a slightly greater 

 facility of distribution, and it is doubtful whether this is 

 not more than neutralised by the labour of mixing. At any 

 rate, one strong argument against mixing them is that they 

 should not, as a rule, be applied at the same time of 

 year. Superphosphate should be applied some time 

 before the seed is sown, and nitrate of soda not until 

 after it has germinated. Superphosphate may, if desired, 

 be mixed with sulphate of ammonia. These manures 

 do not act upon each other and there is less reason for 

 not applying them at the same time than in the case 

 of nitrate of soda. For those who are at all uncertain 

 of the chemistry of the subject, the only safe rule is not 

 to mix superphosphate with anything before applying 

 it to the land, but there is no reason why any manure 

 should not be applied to the same soil that has already 

 received a dressing of superphosphate. It may also be 

 safely mixed with sulphate of potash and a mixture of 

 this kind can be obtained commercially. It is called 

 " Potassic superphosphate," and contains about 23 per 



1 The reaction may be more complex than is shown here. 



