50 FERTILISERS CONTAINING NITROGEN [chap. 



The salt is very soluble in water and is deliquescent, 

 so that it will gradually absorb enough water to liquefy 

 when exposed to the damp air of an English winter in 

 a manure shed. The salt is poisonous in quantity, and 

 both horses and stock have not infrequently been killed 

 by licking nitrate of soda or the bags in which it has 

 been stored. Nitrate of soda contains as much as 56 

 per cent, of oxygen and accelerates the combustion of 

 such bodies as wood or coal with almost explosive 

 violence, one accident at least has been recorded from 

 this source of danger. Nitrate of soda is not only 

 soluble in water, but it is not in any way retained by 

 the soil, so that it must wash through into the drains or 

 subsoil when percolation is going on. For this reason 

 it should only be applied as a top dressing when the 

 crop is growing. Like all other saline bodies which 

 form a strong solution with water, nitrate of soda will 

 scorch and destroy any green tissue with which it is left 

 in contact ; it withdraws water from the cells and kills 

 them by plasmolysis (see p. 18). Hence in sowing 

 nitrate of soda on a crop like cabbage, a certain amount 

 of care should be taken not to let the salt lodge in 

 the crown of the plant. 



Nitrate of soda may be mixed with other manures 

 except superphosphates and dissolved bones, the acid of 

 which gradually liberates nitric acid, so that such a 

 mixture should be sown immediately after it has been 

 made. 



Nitrate of soda is always sold by the producers with 

 a guarantee of 95 per cent, pure, which guarantee 

 should also be obtained by the farmer, for the material 

 should be sold exactly as it is imported. It usually 

 contains about 96 per cent, of pure sodium nitrate, 

 which is equivalent to 157 per cent, of nitrogen or 191 

 per cent, of ammonia. 



