the boiling-point of alcohol, with occasional shaking. After standing for an hour, the hot liquid is decanted upon a 10-cm. filter, and 25 cc. of the hot alcohol are added to the residue and shaken, after which the residue is again allowed to settle, and the liquid decanted. This is repeated six times. The remainder of the alcohol is then driven off by evaporation, and the nitrogen determined in the residue. The difference between the total nitrogen and the nitrogen thus obtained, gives the nitrogen of the alcoholic extract, which includes the amides. Subtracting the latter, or amido-nitrogen, the remainder is the gliadin nitrogen. Glutenin Nitrogen.-This is the difference between the gluten nitrogen and the gliadin nitrogen. The factor by which the nitrogen should be multiplied in determining the various proteins, according to Osborne and Voorhees, is 5.7 for wheat. Proteins of the Common Cereals and Vegetables.-Osborne and his coworkers have made a detailed study of the protein constituents not only of wheat as above outlined, but of other common grains and vegeta bles, and the results of these investigations may be thus briefly sum marized: Soluble in dilute alcohol: Zein..... Insoluble in above, but soluble in two-tenths per cent potash solution... Protein of pea: § Soluble in salt solution: Globulins { Legumin.. Soluble in water: Albumin, legumelin, proteose... Per Cent. 0.3 1.95 4.00 4.50 0.06 0.04 0.25 1.10 5.00 3.15 7.00 3.00 2.03 * Jour. Am. Chem. Soc., 17, page 429. † Ibid., 17, P, 539. § Ibid., 18, p. 583; 20, pp. 348 and 410. MINERAL CONSTITUENTS OF CEREALS AND VEGETABLES. The food analyst often finds the determination of one or more of the mineral constituents of a food product of value as a means of detecting adulteration, since the addition of foreign material may alter materially the composition of the ash. The following table * shows the composition of the pure ash of common cereals. Snyder † obtained the following average results in the analysis of the ash of 12 samples of wheat: König gives the following analyses of the ash of various leguminous and other vegetables: * U. S. Dept. of Agric., Bur. of Chem., Bul. 13, part 9, p. 1212. † Minn. Agric. Exp. Sta., Bul. 29, 1893, p. 149. 3.57 42.49 1.34 4.73 7.08 0.57 38.74 2.53 0.73 1.57 3.49 0.86 1.54 6.49 2.13 3.11 Scheme for Complete Ash Analysis.-The following scheme in essential details was suggested by the later Prof. S. L. Penfield of Yale University for use at the Connecticut Agricultural Experiment Station. Preparation of Ash.-The amount of material which should be reduced to ash depends on the percentage of total ash present and the amount of material available. Usually 100 grams is a suitable amount; if, however, the material (e.g., tobacco) is rich in ash, 50 grams is sufficient, while if it contains but a small amount of ash, 200 grams or even more may be required. About 5 grams of ash is a liberal amount for a complete analysis, but in case of necessity 1 gram will suffice if care is taken to so adapt the scheme as to make as many determinations as possible on one weighed portion. The ashing is carried on in a platinum dish heated below redness by a Bunsen burner. In order to distribute the heat and prevent overheating, a piece of asbestos paper is introduced between the dish and the flame. The material first chars, then begins to glow just below the surface, and the combustion gradually extends downward until it reaches the bottom of the dish. Then, and not until then, the unburned carbon on the surface should be stirred in with the ash to facilitate burning. Care should be taken not to heat higher than dull redness, thus avoiding the loss of alkali chlorides and the fusion of alkali phosphates about the particles of carbon. A muffle furnace may be used to complete the burning. Substances rich in starch or sugar are most difficult of combustion, as the charcoal forms a hard mass, while substances rich in fibrous or woody matter burn quite readily without losing their powdered condition. A certain amount of unburned carbon is no disadvantage, as it is determined in the course of the analysis. Finally cool the ash, grind to a powder, mix without loss, and weigh, thus determining the percentage of crude ash. Determination of Water.-Heat 1 gram of the ash in a platinum crucible well below redness to constant weight. as Determination of Carbonic Acid. Determine carbonic acid described on p. 353 using the portion dried for the determination of water. Determination of Charcoal and Sand.-Weigh 1 gram of the ash, or transfer the solution and residue from the determination of carbonic acid, into a beaker, add 25 cc. of water and 25 cc. of 10 per cent hydrochloric acid, and boil gently for 10 minutes. Filter on a Gooch crucible, and wash thoroughly with hot water. Reserve the filtrate for determination of silica, iron oxide, alumina, lime, and magnesia. Wash the residue on the crucible once with alcohol and once with ether, and dry to constant weight at 100° C. Ignite and weigh again. The loss on ignition is the charcoal, the residue is sand. Determination of Silica, Iron Oxide, Alumina, Lime and Magnesia.— Evaporate to dryness in a platinum dish the filtrate from the determination of charcoal and sand, heat for some hours on the water bath, and dry at 130° C. until all hydrochloric acid is removed. Moisten the residue thoroughly with concentrated hydrochloric acid, add hot water, stir, and decant the solution on an ashless filter. Treat the residue again with acid and hot water, and repeat the treatment until nothing but silica remains undissolved. Finally collect the silica on the paper, wash with hot water, ignite in a platinum crucible, and weigh. To the filtrate add ammonia until a precipitate forms which remains on stirring, and then add sufficient hydrochloric acid to just dissolve the precipitate. Heat to 50° C. and add an excess of ammonium acetate solution and 4 cc. of 80 per cent acetic acid. Digest at 50° C. until the mixed phosphates of iron and alumina have settled, filter, wash with hot water, ignite in a platinum crucible, and weigh. As the precipitate is usually slight and consists almost entirely of iron phosphate, the iron oxide may be calculated with reasonable accuracy using the factor 0.53. If, however, greater accuracy is desired fuse the weighed precipitate with 10 parts of sodium carbonate, dissolve in dilute sulphuric acid, reduce with hydrogen sulphide, determine iron by the volumetric permanganate method, and in the same solution determine phosphoric acid by the molybdic method. The alumina is obtained by difference, subtracting the sum of the weights of the oxide of iron and phosphoric acid from the total weight of the precipitate. To the filtrate from the mixed phosphates add an excess of ammonium oxalate, allow to stand in a warm place over night, filter, ignite the precipitate in a platinum crucible over a Bunsen burner, and finally to constant weight over a blast lamp, thus obtaining the calcium oxide. Precipitate the magnesia in the filtrate from the lime by adding ammonia to alkaline reaction, then an excess of sodium phosphate solution with constant stirring, and finally sufficient concentrated ammonia to form one-tenth the final volume. Let stand over night, collect the magnesium ammonium phosphate on a Gooch crucible, ignite to magnesium pyrophosphate, and weigh. Determination of Sulphuric Acid, Potash, and Soda.-Boil 1 gram of the ash with dilute hydrochloric acid, and remove charcoal, sand, and silica, as described in the preceding section. Evaporate nearly to dryness to remove the excess of acid. Dilute to 100 cc., heat to boiling, and add barium chloride solution drop by drop until the sulphuric acid is precipitated. Allow to stand over night, filter, ignite, and weigh as BaSO4. Heat the filtrate to boiling, add enough barium hydroxide to make the solution strongly alkaline, filter, and proceed with the determination of potash and soda, as described on p. 361. Determination of Phosphoric Acid.-Dissolve 0.5 gram of the ash in hydrochloric acid, filter, and wash. Neutralize with ammonia, clear with nitric acid, and proceed as described on p. 362. Determination of Chlorine.-Dissolve 1 gram of the ash in cold, very dilute nitric acid, filter, and wash. To the filtrate add an excess of silver nitrate, and heat nearly to boiling with constant stirring. Filter on a Gooch crucible, wash with hot water, dry the precipitate at a low heat, and heat cautiously at dull redness until the silver chloride has partially melted. If desired the chlorine may be determined volumetrically by Volhard's method, as follows: To the nitric acid solution add a known volume of decinormal silver nitrate solution sufficient to precipitate the chlorine, and 5 cc. of saturated solution of ferric alum. Titrate with decinormal ammonium thiocyanate solution until a permanent brown color is formed. Subtract the volume required from the volume of decinormal silver nitrate added, and calculate the chlorine. Determination of Sulphur in Vegetable Materials.*-Place from 1.5 to 2.5 grams of material in a nickel crucible of about Ico cc. capacity *A. O. A. C. Method, U. S. Dept. of Agric., Bur. of Chem., Bul. 107 (rev.), pp. 23, 24. |