14 PROVISIONAL METHODS FOB ANALYSIS OF FOODS. 



found that the proteids are so completely removed that no precipitate is formed with 

 the double iodid. In such case nitration is not necessary. 



Add about 2 mg of sodium chlorid per 100 cc of water, precipitate the glycogen 

 again by means of two volumes of 96 per cent (sp. gr. 0.81) alcohol, filter, wash with 

 96 per cent alcohol, containing about 7 mg of sodium chlorid per liter, then with 

 absolute alcohol, finally with ether, dry to constant weight, and weigh. 



As a control, invert the precipitated glycogen by boiling for three hours with hydro- 

 chloric acid diluted with 10 parts of water and determine the reducing sugar by 

 Allihn's method, multiplying the result by 0.9 for percentage of glycogen. 



10. DETERMINATION OF REDUCING SUGAR. 



Boil 100 grams of the finely divided meat for fifteen or twenty minutes in a 500-cc 

 graduated flask with a convenient volume of water. Add a few cubic centimeters of 

 normal lead acetate, cool to room temperature, make up to mark with water, and 

 filter through a fluted filter. Evaporate to a small volume as large an aliquot portion 

 of the filtrate as possible, add a saturated solution of sodium sulphate, make up to a 

 definite volume, and filter through a fluted filter. Determine sugar in an aliquot 

 portion of the filtrate by the Allihn method (p. 49). 



11. DETERMINATION OF POTASSIUM NITRATE. 



(a) METHOD OF SCHLOSING-WAGNER. a 



A flask of about 250-cc capacity is provided with a rubber stopper with two holes. 

 Through one of them is passed the stem of a funnel carrying a glass stopcock. The 

 other carries a delivery tube leading to the receiving vessel. The end of the delivery 

 tube is bent so as to pass easily under the mouth of the measuring burette and is 

 covered with a piece of rubber tubing. 



Fifty cubic centimeters of saturated ferrous chlorid solution and the same quantity 

 of 10 per cent hydrochloric acid are placed in a flask. The ferrous chlorid solution is 

 prepared by dissolving nails or other small pieces of iron in hot hydrochloric acid 

 and is kept in glass-stoppered flasks of about 50-cc capacity, entirely filled. The 

 contents of one flask is enough for about twelve determinations, and by using the 

 whole content of a flask as soon as possible after opening, all danger of oxidation 

 which would take place in a large flask frequently opened is avoided. 



The contents of the flask are boiled until all the air is driven off. The delivery 

 tube is then placed under the measuring tube, which is filled with 40 per cent 

 potassium hydroxid, then a few drops of water are added and the tube is covered with 

 a piece of filter paper. By a careful and quick inversion, the measuring tube can be 

 brought into the vessel receiving it without any danger of air entering. 



One hundred grams of the finely macerated meat are extracted by boiling repeatedly 

 with successive small volumes of water, the aqueous solution is concentrated to a 

 small volume, transferred to the funnel, and, with continued boiling, allowed to pass, 

 drop by drop, into the flask. When almost all has run out, the funnel is washed with 

 three 10-cc portions of 10 per cent hydrochloric acid and these portions are allowed 

 to pass, drop by drop, into the flask; the temperature of the surrounding water will 

 soon be imparted to the contents of the tube, and the volume of nitric oxid is 

 read with the tube in such a position that the level of the water within and without 

 the tube coincide. 



The amount of nitric oxid present and the corresponding percentage of nitrate may 

 be calculated in the usual way for the given temperature and barometric pressure, or, 

 to avoid computation, the amount of nitrate may be determined by comparison of the 



Agr. Chem. Vers. Stat. Halle, i>. 50; Wik-y, Principles and Practice of Agricultural Analysis, vol. 2, 

 p. 228. 



