12 METHODS OF ANALYSIS (Chap. 



(b) Raw materials. — Place an amount of material, equivalent to 50 mg. of water- 

 insoluble organic nitrogen determined as directed under 36, in a small mortar, add 

 about 2 grams of powdered rock phosphate, mix thoroughly, transfer to a filter paper, 

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

 When much oil or fat is present, it is well to wash with ether before extracting with 

 water. 



39 DETERMINATION. 



Dry the residue of 38 at a temperature not exceeding 80°C. and transfer from the 

 filter to a 500-600 cc. Kjeldahl distillation flask. Add 20 cc. of water, 15-20 small 

 glass beads, or fragments of pumice stone, a piece of paraffin the size of a pea, and 

 100 cc. of alkaline permanganate solution (25 grams of pure potassium permanganate 

 and 150 grams of sodium hydroxid, separately dissolved in water, the solutions cooled, 

 mixed, and made to a volume of 1 liter). Connect with an upright condenser to 

 the lower end of which a receiver containing standard acid has been attached. 

 Digest slowly, for at least 30 minutes, below distillation point, with a very low flame, 

 using coarse wire gauze and asbestos paper between the flask and flame. Gradually 

 raise the temperature and, after any danger from frothing has passed, distil until 

 95 cc. of the distillate are obtained, and titrate as usual. When a tendency to froth 

 is noticed, lengthen the digestion period and no trouble will be experienced when the 

 distillation is begun. During the digestion gently rotate the flask occasionally, 

 particularly if the material shows a tendency to adhere to the sides. The nitrogen 

 thus obtained is the active water-insoluble organic nitrogen. 



Method I. 

 Lindo-Gladding Method. — Official. 



40 REAGENTS. 



(a) Ammonium chlorid solution. — Dissolve 100 grams of ammonium chlorid in 

 500 cc. of water, add 5-10 grams of pulverized potassium-platinic chlorid, and shake 

 at intervals for 6-8 hours. Allow the mixture to settle overnight and filter. The 

 residue may be used for the preparation of a fresh supply. 



(b) Platinum solution.— A. platinic chlorid solution containing the equivalent of 

 1 gram of metallic platinum (2.1 grams of H2PtCl6) in every 10 cc. 



(C) 80% alcohol.— Sp. gr. 0.8645 at -^^. Denatured alcohol, made up according 

 to formula 1 (U. S. Internal Rev., Reg. No. 30, Revised, Aug. 22, 1911, p. 45) and di- 

 luted with water to make 80% alcohol by volume, may also be used. 



41 PREPARATION OP SOLUTION. 



(a) Mixed fertilizers.— Tlace 2.5 grams of the sample upon a 12.5 cm. filter paper 

 and wash with boiling water until the filtrate amounts to about 200 cc. Add to the 

 filtrate 2 cc. of concentrated hydrochloric acid, heat to boiling, transfer to a 250 cc. 

 graduated flask and add to the hot solution a slight excess of ammonium hj-droxid 

 and sufficient ammonium oxalate to precipitate all the lime present, cool, dilute to 

 250 cc, mix, and pass through a dry filter. 



(b) Potash salts; jnuriate and sulphate of potash, sulphate of potash and magnesia, 

 and kainit. — Dissolve 2.5 grams and dilute to 250 cc. without the addition of am- 

 monium hydroxid and ammonium oxalate. 



(C) Organic compounds.— W^hen it is desired to determine the total amount of 

 potash in organic substances, such as cottonseed meal, tobacco stems, etc., saturate 



