116 Fertilizers 



Powder waste. 



Powder waste also consists largely of common salt, 

 though frequently containing appreciable percentages 

 of nitrogen in the form of a nitrate. Its use can only be 

 recommended when it can be obtained at a low price per 

 ton, or for the handling, and upon soils that show a marked 

 benefit from its application. 



Gas lime. 



"In gas works, quicklime is used for removing the impuri- 

 ties from the gas. Gas lime, therefore, varies considerably 

 in composition, and consists really of a mixture of slaked 

 lime, or calcium hydrate, and carbonate of lime, together 

 with sulfites and sulfides of lime. These last are injurious 

 to young plant life, and gas lime should be applied long 

 before the crop is planted, or at least exposed to the air 

 some time before its application. The action of air con- 

 verts the poisonous substances in it into non-injurious 

 products. Gas lime contains on an average 40 per cent of 

 calcium oxide, and usually a small percentage of nitrogen." 



Where it can be used to advantage, its cost should, as 

 in the case of the other, be based on the proportion of 

 actual lime present. 



Gypsum or calcium sulfate. 



Gypsum is a sulfate of lime, containing water in com- 

 bination. Pure gypsum contains 32.5 per cent of lime, 

 46.5 per cent of sulfuric acid and 21 per cent of water. 



Plaster of paris is prepared from gypsum by burning, 

 which drives off the water it contains. 



Gypsum, like other forms of lime, furnishes directly 

 the element calcium, and also exerts a favorable solvent 

 effect upon the soil. It was formerly used in large quan- 



