FERTILIZERS. 51 



formation of the organic portion of the plant. Besides 

 this direct support of plant-growth, they serve, also, the 

 very important purpose of increasing the supply of inor- 

 ganic plant-food ; for they aid in the disintegration of the 

 soil." 



Sulphate of ammonia, a by-product of works where coal 

 is used for the manufacture of gas, is one of the princi- 

 pal sources for nitrogen. It looks like rather coarse salt, 

 and is marketed from barrels up to huge tierces weigh- 

 ing from a thousand to fifteen hundred pounds. It is 

 readily soluble in water, but does not waste in the air. 

 Nitrate of potash (saltpetre) is usually too dear a source 

 for nitrogen to make it available. Nitrate of soda is 

 found in the interior of Chili, on the surface and in the 

 soil. It is a remarkably stimulating fertilizer, and, if there 

 is much rain, will waste before plants can take it up. Mr. 

 Lawes advises to apply it only when not more than three 

 feet in depth of the soil will be moistened. From one 

 hundred to two hundred pounds per acre is excellent to 

 give grass a start in the spring : it should not be applied 

 before the leaf has made a growth of three or four inches. 

 In dry seasons it is better and cheaper than sulphate of 

 ammonia, as the latter needs a degree of moisture to make 

 plant-food. Still, on the whole, the sulphate of ammonia 

 is considered the better investment: for, (1) it is not 

 likely to be lost in the atmosphere ; (2) it is not too solu- 

 ble ; (3) it has the power of clinging to the ingredients 

 of the soil, clay will hold it persistently, and even pure 

 sand, when washed with water, will retain a large portion 

 of it ; (4) its ammonia is easily changed into nitric acid 

 by ingredients in the soil. Nitrate of soda, we are told, 

 "is very liable to be adulterated with white sand or 

 broken quartz, and with salt or the cheap potash salts. 

 . . . The purchaser should see that it dissolves entirely in 

 water, and does not taste distinctly of salt." 



