NITROGEN AS NITRATE 



207 



to loosen up the masses of caliche and to break up the 

 overlying strata. From the mines the crude material is 

 taken to the works where it is dissolved in hot water, trans- 

 ferred to evaporating tanks, and the sodium nitrate allowed 

 to crystallize out (Fig. 4(i). It is then dried and sacked 

 for shipment. As it comes on the market nitrate of soda 

 is coarsely granular material, brown, gray, or pink in color 

 and most of it is about 90 per cent, pure, containing in 

 addition to sodium nitrate, some moisture, sodium chloride, 

 calcium, magnesium, and sodium sulphates. The nitrogen 

 content is nearly 16 per cent. 



Fig. 46. — Nitrate of soda in crystallizing pans. 



(6) Availability. — Since nitrate of soda is very soluble, 

 one part dissolving in about one part of water, and, more- 

 over, since its nitrogen is in the form which plants require, 

 it is an immediately available fertilizer. In addition to its 

 being very soluble it is not fixed or retained by the soil 

 to any extent, and is therefore easily lost by leaching. Con- 

 sequently applications of sodium nitrate should be made a 

 very short time before seeding, or as a top dressing. 



(c) Effect on the Soil. — In the soil sodium nitrate serve> 

 as an indirect fertilizer in that it reacts with insoluble potas- 

 sium compounds, making the potassium soluble. Experi- 



