10 



MANIPULATION. 



(1) TJie digestion. From 0.7 to 3.5 grams of the substance to be analyzed, according 

 to its proportion of nitrogen, are brought into a digestion flask with approximately 0.7 

 gram of mercuric oxid or its equivalent in metallic mercury and 20 c. c. of sulphuric 

 acid. The flask is placed in an inclined position, and heated below the boiling point 

 of the acid for from five to fifteen minutes or until frothing has ceased. If the mix- 

 ture froth badly, a small piece of paraffin may be added to prevent it. The heat is 

 then raised until the acid boils briskly. No further attention is required till the 

 contents of the flask have become a clear liquid, which is colorless, or at least has 

 only a very pale straw color. The flask is then removed from the frame, held upright, 

 and, while still hot, potassium permanganate is dropped in carefully and in small 

 quantities at a time till, after shaking, the liquid remains of a green or purple color. 



(2) The distillation. After cooling, the contents of the flask are transferred to the 

 distilling flask with about 200 c. c. of water, with a few pieces of granulated zinc, 

 pumice stone, or 0.5 gram of zinc dust when found necessary to keep the contents of 

 the flask from bumping, and 25 c. c. of potassium-sulphid solution are added, shaking 

 the flask to mix its contents. Next add 50 c. c. of the soda solution, or sufficient to 

 make the reaction strongly alkaline, pouring it down the side of the flask so that it 

 does not mix at once with acid solution. Connect the flask with the condenser, mix 

 the contents by shaking, and distil until all ammonia has passed over into the stand- 

 ard acid. The first 150 c. c. of the distillate will generally contain all the ammonia. 

 This operation usually requires from forty minutes to one hour and a half. The 

 distillate is then titrated with standard alkali. 



The use of mercuric oxid in this operation greatly shortens the time necessary for 

 digestion, which is rarely over an hour and a half in case of substances most diffi- 

 cult to oxidize, and is more commonly less than an hour. In most cases the use of 

 potassium permanganate is quite unnecessary, but it is believed that in exceptional 

 cases it is required for complete oxidation, and in view of the uncertainty it is 

 always used. The potassium sulphid removes all the mercury from the solution, 

 and so prevents the formation of mercur-ammonium compounds which are not com- 

 pletely decomposed by soda solution. The addition of zinc gives rise to an evolu- 

 tion of hydrogen and prevents violent bumping. Previous to use the reagents should 

 be tested by a blank experiment with sugar, which will partially reduce any nitrates 

 that are present, which might otherwise escape notice. 



MOIST GLUTEN. 



Place 10 grams of the sample in a porcelain dish and moisten with 

 from 6 to 7 c. c. of cold water, knead, and allow to stand for an hour. 

 Work into a ball, being careful that none of the material adheres to the 

 dish. Holding the mass in the hand knead it in a slow stream of cold 

 water until the starch and all soluble matter are washed out. Place 

 the ball of gluten thus formed in cold water and allow to stand for one 

 hour; remove from the water, press as dry as possible between the 

 hands, roll into a ball, and weigh in a flat-bottomed dish. 



DRY GLUTEN. 



After weighing place the ball of moist gluten in the drying oven at a 

 temperature of boiling water for twenty-one hours; cool and weigh. 



CRUDE FIBER. 



The residue from the ether extract may be used for this determina- 

 tion. To this residue in a half liter flask or beaker add 200 c. c. of boiling 

 1.25 per cent sulphuric acid. Continue the boiling for thirty minutes, 



