MANURES 107 



(A) Nitrogenous Manures. — The principal members of this 

 class are sodium nitrate and ammonium sulphate. 



Sodium Nitrate. — " Chili saltpetre " or " cubic nitre " is 

 found in certain rainless districts in Peru, Chili, and Bolivia. 

 It occurs near the surface in layers varying in thickness from 

 a few inches to 12 feet. The crude deposit is known as caliche^ 

 and varies greatly in composition. The different varieties 

 are mixed so as to yield a product containing : 



Per cent. 



Earth, stones, &c. 50 



Sodium nitrate 35 



Magnesium, calcium, and sodium chlorides . 10 



Water, sulphates, and other substances . . 5 



This mixture is treated with water and allowed to settle; 

 iodine, which is present as sodium iodate, NalOg, is extracted, 

 and the liquor evaporated and crystallised. The crystals 

 so formed, are dried by exposure to the sun, and exported. 

 The average composition of the commercial product is said 

 to be: 



10)-00 



During recent years much attention has been directed 

 to the presence of sodium perchlorate, KaClO^, in many 

 samples of nitrate, and to the injurious effects produced by 

 the application of such nitrate to many crops. Specimens 

 of nitrate of coda have been found to contain as much as 5 

 per cent, of this poisonous perchlorate, and in samples used 

 in Germany, an average of about 1 per cent, appears to be 

 present. English samples seem to be comparatively free from 

 this impurity. Pure sodium nitrate, NaN03, ^^ ^ white 

 crystalline salt, very soluble in water (100 parts of water dis- 

 solving about 80 parts of the salt at ordinary temperatures), 

 and debXuescent in moist air. It is not retained by any 



