134 ELEMENTS OP ACHtlCtTLTttltE 



2. Sulphate of ammonia is another salt containing* 

 nitrogen, and is used to some extent as a fertilizer. It 

 is made up of the elements nitrogen, hydrogen, sul- 

 phur and oxygen, and contains about 20 per cent of 

 nitrogen. Sulphate of ammonia is produced as a by- 

 product by gas works which manufacture illuminating 

 gas for cities and towns. It is easily soluble in water, 

 but in the soil must be changed to a nitrate before it 

 becomes plant food. 



Nitrate of soda and sulphate of ammonia are the 

 only salts of nitrogen used for fertilizers. A large part 

 of the nitrogen of fertilizers comes from organic com- 

 pounds, such as cottonseed-meal, bones, dried blood, 

 fish scrap, etc. 



3. Cottonseed-meal is a by-product from the manu- 

 facture of oil from cottonseed, and is now produced in 

 immense quantities. In the oil mills the cottonseed 

 first have the hulls — the hard outer shell from which 

 the lint grows — taken off by machinery. The soft 

 inner portion of the seed, called the kernel, is then 

 heated in immense kettles, after which process it is 

 pressed much as apples are pressed for cider, only the 

 presses are much more powerful. Most of the oil which 

 the seed contains is pressed out by this process, and 

 the remainder of the kernels formed into a flat cake 

 which from the great pressure is as hard as a board. 

 In this form it is called cottonseed-cake, and before 

 it can be used must be ground up in mills, from which 

 it comes as cottonseed-meal, a substance of a rich, 

 golden yellow color, and about as coarse as corn-meal. 



Great quantities of cottonseed-meal are produced 



