Total Crude Protein.—Determine nitrogen as directed for nitrogen in fertilizers and multiply the result by 6.25 for the crude protein.
Determination of Albuminoid Nitrogen.—To from seven-tenths to eight-tenths gram of the substance in a beaker add 100 cubic centimeters of water, heat to boiling, or in the case of substances rich in starch, heat on the water-bath ten minutes, and add a quantity of cupric hydroxid mixture containing from one-half to six-tenths gram of the hydroxid; stir thoroughly, filter when cold, wash with cold water, and put the filter and its contents into the concentrated sulfuric acid for the determination of nitrogen. The filter-papers used must be practically free of nitrogen. Add sufficient potassium sulfid solution to completely precipitate all copper and mercury, and proceed as in the moist combustion process for nitrogen. If the substance examined consist of seed of any kind, or residues of seeds, such as oil-cake or anything else rich in alkaline phosphates, add a few cubic centimeters of a concentrated solution of alum just before adding the cupric hydroxid, and mix well by stirring. This serves to decompose the alkaline phosphates. If this be not done cupric phosphate and free alkali may be formed, and the protein-copper may be partially dissolved in the alkaline liquid.
Cupric Hydroxid.—Prepare the cupric hydroxid as follows: Dissolve 100 grams of pure cupric sulfate in five liters of water, and add twenty-five cubic centimeters of glycerol; add a dilute solution of sodium hydroxid until the liquid is alkaline; filter, rub the precipitate up with water containing five cubic centimeters of glycerol per liter, and then wash by decantation or filtration until the washings are no longer alkaline. Rub the precipitate up again in a mortar with water containing ten per cent of glycerol, thus preparing a uniform gelatinous mass that can be measured out with a pipette. Determine the quantity of cupric hydroxid per cubic centimeter of this mixture.
Amid Nitrogen.—The albuminoid nitrogen determined as above subtracted from the total, gives that part of the organic nitrogen existing in the sample as amids and in other allied forms.
204. Separation of Nitric and Ammoniacal from Organic Nitrogen.—The nitrogen being present in three forms, viz., organic, ammoniacal, and nitric, the separation of the latter two may be accomplished by the following procedure:[173] One gram of the fertilizer is exhausted on a small filter with a two per cent solution of tannin, using from thirty to forty cubic centimeters in small portions. This is sufficient to dissolve all the nitrates and the greater portion of the ammoniacal salts, while the tannin renders insoluble all the organic nitrogenous compounds. The filter and its contents are treated for nitrogen by the kjeldahl process. When the distillation and titration are completed the solution obtained by the aqueous tannin is added to the distilling flask and the operation continued. This represents the ammoniacal nitrogen.
The nitric acid is estimated by the ferrous iron or other appropriate method in another portion of the substance.
This method can be used even when the fertilizer contains ammonium magnesium phosphate. In this case digest one gram for fifteen hours in dilute soda-lye solution, which easily dissolves the ammonium magnesium phosphate. Filter and wash the insoluble part with the tannin solution. The residue is treated as above. The filtered solution distilled with soda-lye furnishes the ammonia. The nitrates are estimated by one of the methods above mentioned.
205. Nitric Nitrogen.—The methods of estimating nitric nitrogen, both when present in weighable quantities and as mere traces have been sufficiently described in the first volume. For convenience, however, the standard methods of procedure will be given here. The moist combustion methods adapted to nitrates and the volumetric copper oxid process have already been described. Of the reduction methods the process of Ulsch is one of the easiest of application and also reliable. As practiced by the official chemists the manipulation is conducted as described in the first volume, page 539.
206. Ulsch Method, Applicable to Mixed Fertilizers.—The method of Ulsch which is found to give good results with pure nitrates or with nitrates in the absence of other forms of nitrogen may also be adapted to mixed fertilizers containing nitrogen in more than one form. Street has developed such a method and shown, by analytical data, that it is applicable in a great number of cases.[174] The process is based on the substitution of magnesia for soda in the distillation and is carried on as follows:
Place one gram of the sample in a half liter flat-bottomed flask. Add about thirty cubic centimeters of water, one gram of reduced iron, and ten cubic centimeters of sulfuric acid diluted with an equal volume of water, shake well, and allow to stand for a short time. This will remove the danger of an explosion caused by the otherwise violent action which takes place. Close the neck of the flask with a rubber stopper through which passes a glass dropping-bulb filled with water. The flask having been stoppered, place it on a slab to which a moderate heat is applied. Allow the solution to come slowly to a boil and then boil for five minutes and cool. Add about 100 cubic centimeters of water, a little paraffin, and about five grams of magnesium oxid. Boil for forty minutes, after which time all the ammonia will be distilled, and collect the ammonia in set acid.