Determination of Uranium in Carnotite Ore Glacial Acetic Acid Method WILFREDW. SCOTT,University Southern California, Los Angeles, Calif.
S
OME years ago the author (1) suggested the use of
glacial acetic acid for the separation of uranium from vanadium with the subsequent precipitation of uranium with ammonium hydroxide and ignition to the oxide, UaOs. I n the recent investigation of this method a comparison was made with Low’s method of the separation of vanadium as lead vanadate. The laboratory work was conducted by Ik$&rshallHall Blain under the author’s supervision. The interfering substances in carnotite are silica, iron, aluminum, and vanadium. A synthetic mixture was made from carefully prepared reagents and the separations made according to the procedure outlined by the author (2). Separations of vanadium as lead vanadate, according to directions by Low, with subsequent determination of vanadium were also made on synthetic mixtures. The results are given in Tables I and 11. TABLE I. LEADVANADATE METHODOF Low P R ~ S ~ N T1 SiOa Alios FezOs VaOa
VsOs
Gram 0.2035 0.0717 0.1316 0.2166 0.2521
Gram 0.2026 0.0702 0.1305 0.2174 0.2511
2 Gram 0.2029 0.0706 0.1306 0.2178 0.2506
FOUND 3 4 Gram Gram 0.2025
5 Gram
0.2608
0.2505
.... .... 0.2172
........ .... ....
0.2501
.... .... .... ....
TABLE11. GLACIALACETICACID METHODOF SCOTT PRESENT SiOa
AlrOa FerOa VaOs
UsOs
Gram 0.2035 0.0717 0.1316 0.2166 0.2521
1 Gram 0.2013 0.0706 0.1304 0.2143 0.2514
2 Grant 0.2017 0,0709 0.1307 0.2156 0.2517
3 Gram 0.2021
4 Gram
0.2171 0,2530
0.2149 0.2512
.. .. .. ..
........ ....
The low results by the lead vanadate method are due, possibly, to the occlusion of uranium by lead vanadate. The separation of vanadium from uranium by this method takes a longer time than the glacial acetic acid separation, The following observations were made regarding the details of the glacial acetic acid method: 1. I n the carbonate extraction of uranium the solution should be boiled a t least 30 minutes or, if preferred, the solution may be taken to dryness and gently baked to ensure removal of carbon dioxide. 2. Hydrocholoric acid may be used in place of nitric acid for neutralization of the solutions. 3. Iron and aluminum should be precipitated from cold solution. 4. When testing the acetic-nitric extract for the presence of vanadium, the addition of a drop of hydrochloric acid intensifies the reddish brown color produced by hydrogen peroxide. 5. Enough ammonium salts are generally present in the solution in which the ammonium uranate is to be precipitated to facilitate the precipitation without the addition of more. 6. The uranium should be precipitated from a hot solution by the addition of ammonium hydroxide, drop by drop, with constant stirring.
LITERATURE CITED
5 Gram
.... .... 0.2152 . . I .
0.2515
(1) Scott, W. W., J. IND. ENQ.CHPM., 14, 531 (1922). (2) Scott, W. W., “Standard Methods of Chemical Analysis,” Vol. I, 4th ed., pp. 581c-581d, Van Nostrand, 1925. RECEIVEDNovember 11, 1931.
Apparatus for Calibration of Flowmeters GRANTW. SMITH,University of Minnesota, Minneapolis, Minn.
A
METHOD for the calibration of flowmeters of the resistance-tube type for use with small rates of gas flow is herein described. Its principal advantages are the following: ease and rapidity of operation; the fact that the as is in no way disturbed during the measurement; and the fact that the head of water against which the gas flows is practically zero a t all times, thus ensuring greater accuracy by excluding the “siphon effect’’ in the delivery tube from E to F (see Figure 1). The gas with which the meter is to be used is introduced into the apparatus under pressure from the gasometer or other container in which it is stored. B is a 2-liter Wolff bottle which is to relieve any slight fluctuations in the gas flow. C is the flowmeter. D is an empty balloon flask of about 2-liter capacity, and is fitted with a three-hole rubber stopper. The valve, a, is opened and closed by means of a screw clamp. E is another 2-liter balloon flask containing water, and is fitted with a rubber stopper through which pass the delivery tube from D, the delivery tube from the aspirator bottle, A , which is used as a storage reservoir for water, and the delivery tube through which the water is displaced by the gas. F is a specially constructed pipet with a volume of 100 cc. between two marks above and below the bulb, respectively. The 244
lower end of the pipet may be closed by the screw clamp valve, c. To perform the calibration, water is run into E from A by opening the stopcock b. The water level should be slightly above the level of the pipet end of the delivery tube, as shown at x, so that this tube will not act as a siphon during the process. A
H aspfrolor
.__._.._ bolllr .__.... _ _ . . ... .._ . . . ...... ..._.. . .....
......-
FIGURE 1. APPARATUSFOR CALIBRATION OF FLOWMETERS
.
April 15, 1932
INDUSTRIAL AND ENGINEERING CHEMISTRY
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
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
