246
ANALYTICAL EDITION
alone was used, in the second case the chromium solutions contained an admixture of ferric alum and alum. Fair duplication of solution A colors with those made by potassium dichromate was observed in all cases. More complete tests were then made using solution A in amounts that varied from 0.01 to 0.10 mg. of chromium, with checks that were invariably satisfactory. These results confirmed a number of tests that were obtained in earlier experiments in which potassium permanganate was used as an oxidizing agent instead of hydrogen peroxide. Photographs of these chromium blue developments are readily distinguished from one another, as may be observed in Figure 1. I n making these photographs the range of chromium color distinctions was materially extended by the use of light screens. It is also of interest to note that chromium-developed wool samples may be stripped of their red color by warming with
Vol. 4,No. 2
dilute alkali solution (0.1 N sodium carbonate) without removing the chromium stain. These stains are proportional to the quantity of chromium present. In order to ascertain if the color development herein described is characteristic of chromic acid, parallel experiments were tried on woolen yarn dyed with serichrome blue R using the following acids and salts in amounts equivalent to 1 mg. of metallic chromium: molybdic, tungstic, vanadic, and permanganic acids; also ferrous sulfate, manganous sulfate, and chrome alum. KO change in color was observed. LITERATURE CITED (1) Friedkinder, V., Fortschr. Theerfarbenfabrikation ver. Ind., 3, 791-3 (1896). (2) Schulta, G., Farbstofftabellen (1914) Dye No. 164. RECEIVED October 20, 1931. Contribution 127 of Food Research Division, Bureau of Chemistry and Soils.
Separation and Determination of Calcium and Magnesium 8-Hydroxyquinoline-Saccharate Method A. C. SHEADAND ROY K. VALLA.University of Oklahoma, Norman, Okla.
S
HEAD and Heinrich (2) reported a method for separating
and determining calcium and magnesium in magnesian limestones and dolomites low in silica and iron, which consists in burning the rock to a mixture of the oxides of calcium and magnesium followed by extraction of soluble calcium oxide from insoluble magnesium oxide by a 30 per cent cane sugar solution. The residual magnesia is then titrated after filtration and the mixed oxides are obtained by a titration of the original limestone. From these data rapid and accurate determinations of calcium and magnesium can be obtained. The method is restricted in its application because, if silica is present, calcium silicates insoluble in sugar solutions are formed, and hence a separation of calcium and magnesium is impossible. To obviate these difficulties and to extend the method over a wider range of applications, the 8-hydroxy-quinoline-saccharate method was devised for the separation of the two oxides, leaving the determination by titration substantially as described in the paper cited. Silica and oxides of iron and aluminum are removed from a weighed sample in the usual way, as are also interfering heavy metals, if present. From the hot filtrate, calcium as oxalate and magnesium as 8-hydroxyquinolate ( 1 ) are precipitated together by the addition of the calculated amount of 8hydroxyquinoline dissolved in the required quantity of a hot solution of oxalic acid previously saturated in the cold. The calcium precipitates first from the slightly acid solution. The solution is then gradually made alkaline with ammonium hydroxide until about 10 per cent by volume has been added, and allowed to stand until precipitation is complete (an hour or two). The mixed precipitate is filtered off on paper and washed with 2 to 5 per cent ammonium hydroxide, ignited to the mixed oxides in a porcelain crucible containing a piece of platinum foil, and weighed. I n case the material under examination is a limestone or dolomite, the weighing as mixed oxides can be omitted, as it is much more convenient to obtain these data by a titration of the unburned limestone which seldom carries such impurities as would vitiate the alkalimetric titration. The freshly ignited mixed oxides are then extracted with 30 per cent saccharate solution ( 2 ) . The extraction and washing of the residual insoluble magnesia
are rapid provided that treatment a t this point is prompt, as standing admits of the hydration of magnesium oxide t o magnesium hydroxide which is colloidal in nature. Filtration of magnesium oxide is rapid and hence the solution needs no protection from carbon dioxide in the air. If magnesium hydroxide is formed, additional apparatus is required t o exclude the carbon dioxide. The extraction and washing should not require more than 15 to 20 minutes, as the solution of freshly ignited calcium oxide is rapid and the mixture is not an intimate one because the bulk of the calcium is precipitated out in slightly acid solution before the magnesia precipitates in the strongly alkaline environment. The method as reported in this and the preceding paper ( 2 ) is both rapid and accurate in the hands of a competent chemist. Table I presents some representative results. TABLEI. REPRESENTATIVE RESULTSFOR CALCIUM AND MAGNESIUM OXIDEIN DOLOMITIC LIMESTONES 0.3479 N 0.1256 N MIXED H C l ~ o 8 NaOH OXIDES MgO F O R M ~ O MgO arum Gram &. cc . % 1 0.2178 0.1055 15.0 36.1 6.33 1 (Av. of 6) 0.2178 0.1053 15.0 36.3 6.22 6.38 1 (By gravimetric methods) 2 0.2339 0,1291 15.0 36.1 5.89 2 (Av. of 6) 0.2339 0.$292 15.0 36.2 5.87
% 42.10 42.12 42.00 49.29 49.37
2 (By gravimetric methods) 3 0.2724 0.1428 3 ( - 4 ~o. f 6 ) 0.2724 0.1431 3 (By gravimetric methods) 4 0.2247 0,1170
5.86 3.85 3.83 3.81 20.11
49.19 48.57 48.73 48.46 31.95
60.0 (0.2 N )
31.97 31.96 30.31
($:.$,
20.14 20.08 13.5 21.89 (0.0915 N ) 21.69
(o,$$f2N)
30.67
60.0 (0.2N )
43.25 22.00 (0.0915N )
30.34
21.86 21.48
30.44 30.48
SAMPL~
WT. SAMPLE
4 (Av. of 6) 0,2247 0.1171 4 (By gravimetric methods) 5 0,9910 0,5173 5
0.73885
0.3869
6
0.7369
0.3857
15.0 15.0
37.4 37.4
25.0
51.4
25.0
51.4
5 (Av.) 5 (B. 9. Dolomite 88)
CaO
LITERATURE CITED (1) Berg, Z. anal. Chem.,76,191 (1929). (2) Shead and Heinrioh, IND. ENG.CHEM.,Anal. Ed., 2 , 3 8 8 (1930). RECRIVED December 31, 1931,
