of ammonia nitrogen. Then in order to secure in the ten liters the proper quantity of ammonia there must be added two liters of water containing 230 - 224 = six grams of nitrogen or seven and three-tenths grams ammonia; viz., ninety-four cubic centimeters of 0.967 specific gravity.
2. Molybdate Solution.—Dissolve 125 grams of molybdic acid in dilute two and five-tenths per cent ammonia, avoiding a large excess of the solvent. Add 400 grams of ammonium nitrate, dilute with water to one liter and pour the solution into one liter of nitric acid of 1.19 specific gravity. Allow the preparation to stand for twenty-four hours at 35° and filter.
3. Magnesia Mixture.—Dissolve 110 grams of pure crystallized magnesium chlorid and 140 grams of ammonium chlorid in 700 cubic centimeters of eight per cent ammonia and 130 cubic centimeters of water. Allow to stand several days and filter.
83. Estimation of Lime.—When the lime is to be determined in basic slags some difficulty may be experienced by reason of danger of contamination of the oxalate precipitate with iron and especially manganese, which is often present in slags.
Holleman[68] proposes to estimate the lime in basic slag by a modification of the methods of Classen and Jones. The manipulation is as follows: Fifty cubic centimeters of the solution of slag, equivalent to one gram of substance, are evaporated to a small volume, twenty cubic centimeters of neutral ammonium oxalate solution (one to three) added to the residue and heated on a water-bath with frequent stirring, until the precipitate is pure white and free from lumps. The time required is usually about ten minutes. The precipitate is collected on a filter and washed with hot water until the filtrate contains no oxalic acid. The precipitated calcium oxalate must be snow-white. The filter is broken and the calcium oxalate washed through, first with water and finally with warm, dilute hydrochloric acid (one to one). The calcium oxalate is dissolved by adding fifteen cubic centimeters of concentrated hydrochloric acid, the solution evaporated to a volume of about twenty-five cubic centimeters and ten cubic centimeters of dilute sulfuric acid (one to five), and 150 cubic centimeters of ninety-six per cent alcohol added. After standing three hours or more the precipitate is separated by filtration and washed with ninety-six per cent alcohol until the washings show no acid reaction with methyl orange. The calcium sulfate precipitated is dried to constant weight. This method gives a pure precipitate of calcium sulfate, containing only traces of manganese.
84. Estimation of Caustic Lime.—The lime mechanically present in basic slags is likely to be found as oxid or hydroxid, especially when the sample is of recent manufacture. In the form of oxid the lime may be determined by solution in sugar. In this process one gram of the fine slag meal is shaken for some time with a solution of sugar, as suggested by Stone and Scheuch.[69] The dissolved lime is separated as oxalate by treatment of the solution with the ammonium salt. The calcium oxalate may be determined by ignition in the usual way or volumetrically by solution in sulfuric acid and titration of the free oxalic acid with potassium permanganate solutions. The standard solution of permanganate should be of such a strength as to have one cubic centimeter equivalent to about 0.01 gram of iron. The iron value of the permanganate used multiplied by 0.5 will give the quantity of calcium oxid found.
85. Detection of Adulteration of Phosphatic Slags.—The high agricultural value of phosphatic slags has led to their adulteration and even to the substitution of other bodies. Several patents have also been granted for the manufacture of artificial slags of a value said to be an approximation to that of the by-products of the basic pig iron process.
(1) Method of Blum.—One of the earliest methods of examining basic slag for adulterations is the method of Blum.[70] This method rests upon the principle of the determination of the carbon dioxid in the sample. The basic phosphatic slag is supposed to contain no carbon dioxid. This is true only in case it is freshly prepared. The tetrabasic phosphate, after being kept for some time, gradually absorbs carbon dioxid from the air. As high as nineteen per cent of carbon dioxid have been found in slags which have been kept for a long while. When the slag has absorbed so much of carbon dioxid and water from the air as to be no longer profitable for market, it can be restored to its original condition by ignition.
(2) Method of Richter-Forster.—One of the common adulterants of tetrabasic phosphate is aluminum phosphate. The method of detecting this when mixed with the slag is described by Richter-Forster.[71] The method depends on the fact that soda-lye dissolves the aluminum phosphate, although it does not dissolve any calcium phosphoric acid from the slag. Two grams of the sample to be tested are treated with ten cubic centimeters of soda-lye of from 7° to 8° C. in a small vessel with frequent shaking for a few hours at room temperature. After filtration the filtrate is made acid with hydrochloric and afterwards slightly alkaline with ammonia. With pure basic slag there is a small trace of precipitate produced, but this is due to a little silica which can be dissolved in a slight excess of acetic acid. If, however, the basic slag contain aluminum phosphate, a dense jelly-like precipitate of aluminum phosphate is produced.
(3) Method of Jensch.—Edmund Jensch[72] determines the tetrabasic phosphate in slags by solution in organic acids, and prefers citric acid for this purpose. This method was also recommended by Blum[73].