128 
COTTON 
lizers, we find several materials for supplying 
nitrogen : 
Nitrate of Soda or Chili Salt-peter is a white 
solid which is mined in the rainless districts of 
South America, especially in Chili and Peru. 
When prepared for commercial use it contains 
from 15J to 16 per cent of nitrogen or 320 pounds 
to the ton. 
Nitrate of soda dissolves easily in water, and 
rapidly distributes itself through the soil where 
plant roots can make use of it. The plants take 
their nitrogen from the soil in the form of nitrate, 
regardless of the source of supply, hence this 
material is the most immediately available form 
of plant food found in commercial substances. 
When used in large quantities there is danger of 
loss because of the ease with which the material 
becomes soluble. 
Sulphate of Ammonia: — This substance con- 
tains about 20 per cent of nitrogen or 400 pounds 
to the ton. While quite available it must be 
changed first into nitrate form before being used by 
plants. 
Dried Blood: — Contains from 8 to 12 per cent of 
nitrogen and 7 to 14 per cent of phosphoric acid, 
and is the richest substance coming from animal 
products. 
Tankage: — A by-product of the slaughtering 
house, contains from 4 to 8 per cent of nitrogen and 
7 to 14 per cent of phosphoric acid. It slowly de- 
composes in the soil, but is a valuable material 
for cotton fertilizers. 
Dried Fish Scrap: — This substance is a by- 
product of the fish oil and canning factories. It 
contains both nitrogen and phosphorus, there 
