28 THE CHEMISTRY OF THE FARM. 



for turnips, but such guanos are more usually converted 

 into superphosphate before they are applied to the land. 



Sulphate of Ammonium. — This substance is prepared 

 from the ammoniacal products of gas works ; in its 

 crystallised form it is the most highly nitrogenous of all the 

 manures at a farmer's disposal, containing about 20 per 

 cent, of nitrogen. 



It should be ascertained in every case that the manure 

 is free from sulphocyanate of ammonium, as this substance 

 is very injurious to plants. If sulphocyanates are present 

 a solution of the salt will become blood-red on the addition 

 of ferric chloride. 



Sulphate of ammonium is a " special " manure, valuable 

 solely for its nitrogen. It is a powerful manure for corn 

 crops, for which it is best employed in conjunction with 

 superphosphate. 



Nitrate of Sodium. — An enormous deposit of the crude 

 salt, containing much chloride of sodium, is found in Peru. 

 The nitrate sent to this country has been purified by 

 crystallisation; it will contain about 15.6 per cent, of 

 nitrogen. The most usual impurity is common salt. 



This manure, like the preceding, is valuable solely for 

 its nitrogen, It is an excellent manure for all crops 

 requiring artificial supplies of nitrogen, especially corn 

 crops and mangels. For corn crops it is best employed 

 together with superphosphate. Nitrate of sodium should 

 not be mixed with a damp superphosphate, else nitric acid 

 may be lost. It is best to mix the two immediately 

 before use ; or the superphosphate may be sown with the 

 corn, and the nitrate applied afterwards as a top dressing. 



