130 Analysis and Valuation of Manures [205,206 



ANALYSIS OF BASIC SLAG 



205. a. The moisture is estimated as usual in 2 grams of sub- 

 stance. It contains neither organic matter nor combined water, 

 as is to be expected from a substance which is produced at the 

 high temperature of the Bessemer converter. 



205. b. Lime and Phosphoric Acid.— The phosphate 

 of lime which is contained in this substance has the formula 

 Ca 4 P 2 9 , and its constitution may be understood by consider- 

 ing it to be a compound of Ca 3 (P0 4 ) 2 and CaO. Thus the 

 four phosphates of lime met with in manures are 



CaO.P 2 5 .2H 2 or CaH 4 P 2 8 , soluble phosphate ; 

 2CaO.P 2 5 .H 2 or Ca 2 H 2 P 2 8 , reverted phosphate ; 

 3CaO.P 2 5 or Ca 3 P 2 8 , "tricalcic phosphate ; 

 4CaO.P 2 5 or Ca^Og, basic phosphate. 



Four methods are given here for the analysis of basic slag. 



206. The first method of analysis is similar to that of 

 mineral phosphates with the following differences : A mixture 

 of nitric and hydrochloric acids, equal parts, is used to dis- 

 solve the substance. This is in order to oxidise the large 

 amount of ferrous oxide present. 



Eight grams of citric acid, and a consequent increase in the 

 amount of ammonia, are used to keep the oxide of iron in 

 solution. Even then the magnesium ammonium phosphate pre- 

 cipitate will contain a trace of iron, and this must be removed 

 by adding '5 gram of citric acid before reprecipitating. For 

 the precipitation of this lime 3 to 4 grams of ammonium oxalate 

 must be used, and the precipitate redissolved and reprecipi- 

 tated. 



The extra amount of citric acid makes the precipitation of 

 the Mg 2 (NH 4 ) 2 (P0 4 ) 2 somewhat slower. The solution must 

 therefore be allowed to stand, with frequent stirring, for two and 



