FERTILIZERS AND PLANT FOOD. 227 



the demand for plant food became greater at home, this trade ceased, 

 and to-day this valuable form of nitrogenous fertilizer is extensively 

 used. Meat and fish scrap are also largely used. 



These are among the principal sources of the three substances, 

 which I have classed as deficient jylant food. 



A word of explanation as to what is meant by phosphoric acid, 

 potash and nitrogen. 



By phosphoric acid is meant a white powder which is made up of 

 the metal phosphorous and the gas oxygen. Chemists express this 

 as PjOj, which means two parts by volume of phosphorus and five 

 parts of oxygen. 



B3' potash is meant a white substance made up of the metal 

 potassium and the gas oxygen, expressed as KjO, or two parts by 

 volume of potassium and one of oxygen. 



By nitrogen is meant the gas which is abundant in its free form 

 in the air. Chemists indicate this by the letter N. 



The term ammonia is used and often misunderstood. It means 

 one part b}' volume of nitrogen and three parts of the gas hj'drogen, 

 or in chemical work written NH3. It must be remembered that 

 when a fertilizer is said to contain a certain amount of ammonia 

 that it really means that it contains nitrogen., but that the amount 

 of nitrogen is only fourteen-seventeenths as much as the amount of 

 ammonia. 



USE OF FERTILIZERS. 



Farmers use fertilizers in the same way that manufacturers use 

 their raw materials. And the same business methods and rules apply 

 in each case. Nitrogen, Phosphoric acid and Potash, or the crude 

 materials containing these are the farmers' raw materials and from 

 them he hopes to manufacture corn, oats, potatoes, ha}', fruit, etc., 

 through the agenc}' of the feoil which is his machine. The following 

 points should be duly considered in this manufacturing process : 



First. The amount of material required by various crops. 



Second. The utilization of all waste 'products, such as animal 

 manures, ashes, etc., which are produced on the farm. 



Third. The purchase of the most economical fertilizing materials 

 as an aid to those home produced fertilizers. 



Fourth. The use of all fertilizers in such a way as to get the 

 most profitable returns in as short a time as possible. 



In all of this the final result must be determined in dollars and 

 cents for this is the true business standard in farming as in manu- 

 facturing. 



