I] FERTILIZERS 11 



34 Zinc-Iron Method. — Official. 



Dissolve 10 grams of the sample in water and dilute to 500 cc. Place 25 cc. of 

 this solution, corresponding to 0.5 gram of the substance, in a 400 cc. distillation flask, 

 add 120 cc. of water, 5 grams of well-washed and dried zinc dust, and 5 grams of 

 reduced iron. To the solution add 80 cc. of saturated sodium hydroxid solution, 

 connect the flask with the condensing apparatus and conduct the distillation .simul- 

 taneously with the reduction, collecting the ammonia in standard acid. Continue 

 the distillation until 100 cc. have been distilled and titrate with standard alkali 

 solution. 



NITROGEN IN NITRATE SALTS. 



35 Ferrous Sulphate-Zinc-Soda Method. — Tentative. 



Place 0.5 gram of the nitrate salt in a 600-700 cc. flask, add 200 cc. of water, 

 5 grams of powdered zinc, 1-2 grams of ferrous sulphate, and 50 cc. of sodium hy- 

 droxid solution (36° Baume). Connect with the distilling apparatus, distil, collect 

 the distillate in the usual way in N/10 sulphuric acid and titrate with standard 

 alkali solution. 



ORGANIC NITROGEN SOLUBLE IN NEUTRAL PERMANGANATE.— OFFICIAL. 



36 Preliminary Test {Determination of Water-Insoluble Organic Nitrogen). 



Place 1 gram of the material on an 11 cm. filter paper and wash with water at 

 room temperature until the filtrate measures 250 cc. Dry and determine nitrogen 

 in the residue, as in 18 or 21, making a correction for the nitrogen of the filter, 

 if necessary. 



37 DETERMINATION. 



Place a quantity of the fertilizer, equivalent to 50 mg. of water-insoluble organic 

 nitrogen as determined in 36, on a moistened 11 cm. filter paper and wash with water 

 at room temperature until the filtrate measures 250 cc. Transfer the insoluble 

 residue with 25 cc. of tepid water to a 300 cc. Griffin low-form beaker, add 1 gram 

 of sodium carbonate, mix, and add 100 cc. of 2% permanganate. Cover with a 

 watch glass and immerse for 30 minutes in a steam or hot water bath so that the level 

 of the liquid in the beaker is below that of the water in the bath. Stir twice at inter- 

 vals of 10 minutes. At the end of the digestion remove from the bath, add immedi- 

 ately 100 cc. of cold water, and filter through a heavy 15 cm. folded filter. Wash 

 with small quantities of cold water until the filtrate measures about 400 cc. De- 

 termine nitrogen in the residue and filter, as in 18 or 21, correcting for the nitrogen 

 contained in the latter. The nitrogen thus obtained is the inactive water-insoluble 

 organic nitrogen. Subtract this result from that obtained in 36 to obtain the 

 percentage of organic nitrogen soluble in neutral permanganate. 



ORGANIC NITROGEN SOLUBLE IN ALKALINE PERMANGANATE.— OFFICIAL. 

 (Not applicable to fertilizers containing cottonseed meal or castor pomace.) 



38 PREPARATION OF SAMPLE. 



(a) Mixed fertilizers. — Place an amount of material, equivalent to 50 mg. of water- 

 insoluble organic nitrogen determined as directed under 36, on a filter paper and 

 wash with water at room temperature until the filtrate measures 250 cc. 



