April 15, 1932
INDUSTRIAL AND ENGINEERING
Stopcock b is then closed, and clamp a is closed. The pipet is left open a t c a t first. The gas flow is then begun, and water flows through the open pipet for a few seconds to allow the flow to become steady. The reading of the meter is noted, and immediately c is closed and the time required by the water to fill the pipet between the two marks is observed with a stopwatch. Three or four check runs should be made without changing the rate of flow. The water level must be kept the same always by letting water run in from the aspirator bottle
CHEMISTRY
245
when necessary. For greatest accuracy, this should be done before each reading. Since the flask E is large, there will be little change in water level during each measurement. Four or five different flow rates should be determined in this manner. Then, plotting the rates of flow in cubic centimeters per minute against the meter readings, a curve may be constructed from which any desired data may be read directly. RECEIVED November 6, 1931.
A New Colorimetric Test for Chromium G. C. SPENCER, Bureau of Chemistry and Soils, Washington, D. C. HILE searching for methods of determining minute quantities of chromium, the writer recalled a dyeing technic in which woolen fiber colored with certain acid dyestuffs is given a subsequent treatment in a bath containing potassium dichromate and sulfuric acid. I n many cases this after-chroming effects a distinct color change on the woolen fabric and greatly increases the fastness of the color. This technic suggested a possible method for the detection of small quantities of chromium by warming previously dyed wool samples in acid solutions that were known or believed to contain chromic acid. Preliminary experiments were accordingly made on woolen yarn that had been dyed with 1 per cent of serichrome blue R (I,.%?) with results which justified further experimentation. This dyestuff, serichrome blue R, despite its name, imparts to wool a bright crimson color with a faint bluish tinge. The deep navy blue shade of the finished wool is developed by chromic acid in the second bath. No other dyestuff seemed to offer any advantages over this for analytical purposes. It is possible that some other dye would be better for quantitative results. For this work wool flock (finely ground wool) was .used, although woolen yarn may be used if preferred. The dyestuff solution was made by dissolving 100 mg. of serichrome blue R in water and making up to 200 cc. The dyeing operations used were the following: To a 125-cc. Erlenmeyer flask were added 40 cc. of water, 0.1 gram of sodium sulfate, and 0.02 gram of sulfuric acid. (The quantities of sodium sulfate and sulfuric acid added represent 5 per cent and 1 per cent, respectively, of the weight of the wool taken.) Two grams of the wool were added and the flask was shaken t o ensure thorough wetting of the fiber. The desired quantity of dyestuff was then added (0.5 per cent is recommended-i. e., 20 cc. of the solution). The mixture was stirred well and heated at full tem erature of the steam bath for 30 minutes, after which it was Ritered on paper by suction in a Buchner funnel, washed free of acid, and dried.
The color standards were prepared as follows: A standard chromium solution was made by dissolving 0.282 gram of potassium dichromate in water and making up to a volume of 100 cc. (1 cc. of this solution contains 1mg. of chromium as Cr.) From this solution a working standard containing 0.01 mg. of chromium in each cubic centimeter was made. To each of ten beakers were added 50 cc. of water, 3 cc. of 1 N sulfuric acid (not standardized), and 0.1 gram of wool previously dyed with serichrome blue R. The mixture was stirred to ensure thorough wetting of the fiber and such quantities of the potassium dichromate solution as represented from 0.01 mg. to 0.1 mg. of chromium were added to the respective beakers, which were then covered with watch glasses. The mixture was heated on a steam bath at full temperature from 20 to 30 minutes with occasional stirring, filtered by suction on paper (small Buchner), washed, dried,
and mounted on a spot plate in Duco household cement thinned down with an equal quantity of amyl acetate. The wool samples thus treated were found to have developed a blue shade in proportion to the amount of chromium which acted on the dyed sample.
FIGURE1. CHROMIC ACID DEVELOPMENTS IN SERICHROME BLUER To test for chromium in unknown samples, separate the chromium, ferric iron, and aluminum in the form of hydroxides. Filter by suction in a Gooch crucible provided with an asbestos mat (preferably on a removable disk) and wash with water. Remove the asbestos with the precipitate to a beaker and add 30 cc. of water and 3 cc. of normal sodium hydroxide solution. Mix well and add 5 cc. of hydrogen peroxide solution (U. S. P.). Allow to stand about 30 minutes, and then warm on a steam bath until hydrogen peroxide is decomposed. Filter by suction and acidify the filtrate with 3 cc. excess of normal sulfuric acid, add with stirring 0.1 gram of dyed wool, and heat the covered beaker on the steam bath from 20 to 30 minutes. Filter by suction on paper, wash, and dry. The presence of chromium is indicated by the development of a blue shade on the red fiber. If this color is not too dark the quantity of chromium may be estimated by comparison with the chromium color standards described above. Confirmation of the method as here presented was made by comparing the colors developed by potassium dichromate solutions with those produced by chromic chloride solutions after oxidation. Both solutions, potassium dichromate and chromic chloride (solution A), were adjusted to contain 0.01 mg. of chromium in 1 cc. The first color standards represented 0.05, 0.07, 0.10, and 0.12 mg. of chromium respectively, besides a blank. I n the first case chromic chloride
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,
