I] FERTILIZERS 5 



water at 65°C. until the volume of the filtrate is about 350 cc, allowing time for 

 thorough draining before adding new portions of water. (1) Transfer the filter 

 and its contents to a crucible, ignite until all organic matter is destroyed, add 10- 

 15 cc. of strong hydrochloric acid, and digest until all phosphate is dissolved; or, 

 (2) Return the filter with contents to the digestion flask, add 30-35 cc. of strong 

 nitric acid, 5-10 cc. of strong hydrochloric acid, and boil until all phosphate is dis- 

 solved. Dilute the solution as prepared in (1) or (2) to 200 cc. If desired, the filter 

 and its contents may be treated according to methods 5 (b), (C) or (d). Mix well, 

 filter through a dry filter and proceed as directed under 6 or 9. 



(b) Non-acidulated samples. — In case a determination of citrate-insoluble phos- 

 phoric acid is required in non-acidulat«d samples treat 2 grams of the phosphatic 

 material without previous washing with water, precisely as in (a), except when the 

 substance contains much animal matter (bone, fish, etc.), in which case dissolve 

 the residue insoluble in ammonium citrate by any one of the processes described 

 under 5 (b), (C) or (d) and determine phosphoric acid as directed in 6 or 9. 



14 CITRATE-SOLUBLE PHOSPHORIC ACID.— OFFICL&L. 



The sum of the water-soluble and citrate-insoluble subtracted from the total 

 gives the citrate-soluble phosphoric acid. 



15 DETECTION OF NITRATES.— OFFICIAL. 



Mix 5 grams of the fertilizer with 25 cc. of hot water and filter. To a portion of 

 this solution add 2 volumes of concentrated sulphuric acid, free from nitric acid and 

 oxids of nitrogen, and allow the mixture to cool. Add cautiously a few drops of a 

 concentrated solution of ferrous sulphate so that the fluids do not mix. If nitrates 

 are present the junction shows at first a purple, afterwards a brown, color or if only 

 a very minute quantity be present, a reddish color. To another portion of the solu- 

 tion add 1 cc. of a 1% solution of sodium nitrate and test as before to determine 

 whether sufficient sulphuric acid were added in the first test. 



ORGANIC AND AMMONIACAL NITROGEN ONLY. 



Kjddahl Method.— Official. 



1 6 REAGENTS. 



For ordinary work N/2 acid is recommended. For work in determining very 

 small amounts of nitrogen N/10 acid is recommended. In titrating mineral acids 

 against ammonium hydroxid solution use cochineal or methyl red as indicator. 



(a) Standard hydrochloric acid. — Determine the absolute strength as follows: 

 Preliminarij test. — Place a measured portion of the acid to be standardized in an 

 Erlenmeyer flask with excess of calcium carbonate, to neutralize free acid, and a 

 few drops of potassium chromate as indicator. By titration with silver nitrate 

 solution determine exactly the quantity required to precipitate the chlorin. Final 

 determination. — To a measured portion of the acid to be standardized add from the 

 burette 1 drop in excess of the required quantity of silver nitrate solution as deter- 

 mined by the preceding test. Heat to boiling, protect from the light, and allow to 

 stand until the precipitate is granular. Filter on a tared Gooch crucible, previously 

 heated to 140°-150°C.. wash with hot water, testing the filtrate to prove excess of 

 silver nitrate. Dry the silver chlorid at 140°-150°C., cool and weigh. 



(b) Standard sulphuric oczcZ.— Determine the absolute strength of the acid by 

 precipitation with barium chlorid solution as follows: Dilute a measured quantity 

 of the acid to be standardized to approximately 100 cc, heat to boiling and add drop 



