278 SOIL AND FERTILIZER ANALYSIS 



materials, such as hair, wool waste, and leather is not per- 

 mitted by some states in making complete fertilizers unless 

 they are treated with sulphuric acid as in the manufacture 

 of "base goods." Their presence in the raw state can be 

 detected with a microscope, and the farmer is thus protected 

 against their use in this condition. 



Water soluble phosphoric acid is monocalcium phosphate, 

 CaH 4 (P0 4 ) 2 , citrate soluble phosphoric acid is the dicalcium 

 phosphate, Ca 2 H 2 (P0 4 )2. It is also called "reverted" phosphate 

 (Section 174). The name "citrate soluble" comes from the 

 fact that it is soluble in a neutral solution of ammonium 

 citrate. Both water soluble and citrate soluble phosphoric 

 acid are available to plants, so that analyses sometimes 

 give only the available phosphoric acid which includes 

 both forms. Insoluble phosphoric acid is tricalcium phos- 

 phate, Ca 3 (P0 4 )2. 



Water soluble potash is a simple determination, and 

 of course is that potash which is readily available to 

 plants. The guaranteed analysis does not state whether the 

 potash is in the chloride or sulphate form, or whether these 

 acid radicles are present. This is sometimes important 

 (Sections 178 and 179), and if so it would be necessary to 

 have the fertilizer analvzed further, or to buv known 

 materials. 



In discussing fertilizers, and sometimes even in naming 

 them, it is customary to use the percentage figures only, 

 in the order of nitrogen, phosphoric acid, and potash. Thus, 

 a 1-6-4 fertilizer is one which contains 1 per cent, nitrogen, 

 6 per cent, phosphoric acid, and 4 per cent, potash. 



In expressing the results of analyses it is sometimes custom- 

 ary to add: "Nitrogen equal to ammonia." This gives a 

 little higher figure and makes the fertilizer look richer than 

 it really is, unless the purchaser is in the habit of thinking of 

 nitrogen in terms of ammonia, the way the fertilizer manu- 

 facturers do. They buy all nitrogenous materials on the 

 ammonia basis. 



In the same way phosphoric acid is sometimes referred to as 



'bone phosphate of lime." Phosphoric acid is P 2 5 , bone 



phosphate is Ca 3 (P0 4 )2. Hence the percentage is more than 



