INDUSTRIAL AND ENGINEERING CHEMISTRY
60
DOUBLE SEPARATION FOR REMOVAL OF MUCH CHLORIDEThe reason for this operation has already been discussed under Effect of Chlorine. The chromic anhydride is added to the bromide, etc., as above described, but the bromine is absorbed in a solution containing 1 per cent sodium thiosulfate with 0.2 per cent sodium carbonate. Place about 10 cc. of this absorbent in each of two 25-cc. test tubes connected one after the other so that the air stream containing bromine is twice washed through the absorbent. After the second tube is a third empty test tube to catch any of the absorbent that may be entrained with the air stream. With this arrangement a more thorough scrubbing of the air stream is accomplished with a minimum of absorbent and more rapid aeration is possible. After about 10 minutes’ operation, wash out the absorbing system into a beaker and evaporate the liquid to about 5 cc. When cool, acidify with dilute sulfuric acid, then transfer to another aerating tube, add chromic anhydride as before, and aspirate the mixture as usual into potassium iodide, and titrate the liberated iodine with sodium thiosulfate as previously described. The amount of chlorine carried over in the first aspiration is so small that practically none of it is carried over with the bromine in the second aspiration. Results
This method has given very satisfactory results during several months’ use in determination of small amounts of bromine in various materials, chiefly the sap of the fresh water alga, Nitella. I n Table I11 are given a few of the results selected from hundreds of determinations. First are a few determinations on pure bromide solutions, made to check the purity of the reagent and correctness of the standard thiosulfate. Following this are a few results obtained when a known amount of bromide was added to a portion of Nitella juice that did not contain bromine. Finally, there are given results of analyses of duplicate portions of Nitella juice from plants grown under varying conditions in solutions containing bromide. The amount of bromine found is calculated as if the specific gravity were the same as that of water. Actually, it is slightly heavier than water, but the error thus introduced is not significant for the purpose for which the analyses were made. Table 111-Analytical
0.01 N NDzSZO~ used cc. 6.22 1.22 0.27 6.16 0.25 6.15 0.23 0.22 0.64 1.19
Results
BROMINEFound MR.
Taken MI. Pure Pofassiiim Bromide 5.0 4.976 1.0 0.976 0.2 0.216 5.0 4.928 0.2 0.200 5.0 4.920 Nitdla Juice Free of Bromine, 1 Cc. 0.2 0.184 0.2 0.176 0.5 0.512 1.0 0.952
Nilella Juice Containing Bromine‘
Errcr Mg.
-0.024 -0.024 +0.016 -0.072 0.000 -0.080 -0.018 -0.024 +0.012 -0.048
P.p.. rn.
in juice 22 0.112 0.14 19 0.096 0.12 32 0.160 0.20 0.I76 35 0.22 58 .. 0.288 0.36 56 0.280 0.35 58 0.288 0.36 0.320 64 0.40 211 1.056 1.32 213 1.064 1.33 1045 5.224 6.53 1066 5.328 6.66 1862 9.312 11.64 1822 9.112 11.39 650 3.248 4.06 656 3.280 4.10 Duplicate determinations were made on two 5-cc. portions of juice.
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Vol. 18, No. 1
Rapid Detection of Small Amounts of Aluminium in Certain Nonferrous Materials”z By G. E. F. Lundell and H. B. Knowles BUREAUOF STANDARDS, WASHINGTON, D. C.
A
S a general rule aluminium is an undesirable constituent in nonferrous materials such as brass, bronze, bearing metals, and spelter, even though the amount is as small as 0.01 per cent. The certain detection of so little aluminium in these materials is difficult enough when attacked leisurely; when the test must be completed in a few minutes-as, for example, while a melt is held-the problem is still more difficult, for distinctive reactions for aluminium are uncommon. Probably the most reliable rapid method for the detection and approximate determination of small amounts of aluminium is that based on the examination of the arc spectra of the material. Under favorable conditions such a determination requires but 10 minutes. The difficulties in the way of this method lie in the cost of the installation, perhaps $1000, and the need for a skilled operator. Methods in which aluminium is finally precipitated as the hydroxide after preliminary separations of copper, iron, and the like are unsatisfactory in that it is difficult to detect the minute precipitate if a moderate-sized sample is used, and there is no guarantee that the precipitate is aluminium hydroxide. In such cases the identification of aluminium, even when mixed with appreciable amounts of white precipitates such as stannic hydroxide, can be made more certain by the use of the new reagent for’ aluminium, the dye aurin tricarboxylic acid, recently described by Hammett and S0tte1-y.~This dye forms a bright red lake with aluminium in acetic acidacetate solution and the lake is stable in ammonium hydroxide-carbonate solution. The test is far superior to that given by sodium alizarin sulfonate, for it requires less time and is more sensitive, particularly in the presence of precipitates such as stannic hydroxide. The authors state that under the conditions of test (1) silicic acid and salts of bismuth, lead, antimony, stannic tin, mercuric mercury, and titanium give white precipitates; (2) salts of cadmium, zinc, manganese, ,nickel, and cobalt give no precipitates; (3) chromium, alkaline earths, and phosphorus do not interfere if ammonium carbonate is present; and (4)iron is undesirable and must be removed. Substances such as sulfur dioxide and hydrogen sulfide that reduce the dye and cause a fading color should be absent when the test is to be held for any length of time; small amounts can be present if immediate comparison is made. The formation of the red aluminium lake is also unsatisfactory if the ammonium carbonatehydroxide solution is added too rapidly or in large excess, or if aluminium is present in very small amount and the lake is formed in the presence of large amounts of other precipitates. In the experiments to be described the final test for aluminium was always obtained in alkaline solution by adding a solution of ammonium carbonate in diluted ammonium hydroxide, slowly and with constant stirring, to a solution containing the dye and free acetic acid. I n such a test the final color of a solution of the dye alone is clear light yellow; 1
Received July 30, 1925.
:Published by permission of the Director, Bureau of Standards, De-
partment of Commerce. :J . A m . Chem. Soc., 41, 142 (1925).
January, 1926
INDUSTRIAL A N D ENGINEERING CHEMISTRY
with aluminium the color ranges from a clear faint pink to a deep red if the amount of aluminium does not exceed 0.1 mg. in 50 cc. of solution; with larger amounts the red lake separates immediately. The use of the dye in an approximate quantitative way is therefore limited to material containing less than 0.1 per cent of aluminium and works best when the percentage is less than 0.05. For these reasons the work centered in establishing a method that would quickly reveal 0.01 per cent or less of aluminium in a 1-gram sample and which would permit an estimation of the amount present. Preliminary Experiments
Preliminary experiments demonstrated that the most satisfactory rapid separations of aluminium from interfering elements are those based on precipitation with sodium hydroxide or a mixture of this reagent with sodium sulfide, the latter along lines already described.4 I n such separations the chief concern is to use resistance glassware of low aluminium content and to obtain a sodium hydroxide reagent that is free from aluminium or contains distinctly less than the amount that is to be sought. Pyrex ware was entirely satisfactory and it was not difficult to get a sodium hydroxide reagent that gave but a faint test in a 5-gram sample. A direct test for aluminium in a solution of the hydroxide is sometimes unsatisfactory because of dissolved iron. The most satisfactory procedure lies in carrying a test through with a sample of copper or brass containing no aluminium. The sodium hydroxide solution had better be prepared frequently rather than stored in glass for any long period. Three methods of preliminary separation are described. I n the first, all the usual elements save aluminium and phosphorus are removed by precipitation with sodium hydroxide-sulfide, filtration, acidification of the filtrate, and a second filtration. This method is the slowest of the three, but can be applied to a greater variety of alloys. I n the second method less sodium sulfide is added and the second filtration is omitted. This method requires but 5 to 10 minutes, and gives satisfactory results with most alloys if care is used to avoid the addition of so much sulfide as to cause the liberation of colored sulfides or hydrogen sulfide when the filtrate is acidified. The judicious use of the sulfide aids in precipitating elements such as lead in lead-base bearing metal and gives a more complete separation of iron in material such as spelter. No sulfide at all is used in the third method, which otherwise resembles the second. This has worked well with brass and such other alloys as give a large precipitate with sodium hydroxide. I n all procedures filtrations are carried along until the papers are fairly well drained and no washing of the precipitate is done. Besides the detection of aluminium in a given material, quite satisfactory estimations of its amount, in the range 0.005 to 0.05 per cent, can be made after a little experience gained in tests of material containing no aluminium and solutions of the same material to which known amounts of aluminium have been added. Method I-Separation of All Ordinary Elements except Aluminium and Phosphorus
Transfer 1 gram of the alloy to a 250-cc. Erlenmeyer flask and dissolve in 5 cc. of concentrated nitric acid. Add 30 cc. of an 8 per cent solution of sodium hydroxide, and heat to boiling as the flask is rotated over a free flame. Boil for 1 minute and add 20 cc. of an 8 per cent solution of sodium sulfide made from the sodium hydroxide solution by saturating a given volume with hydrogen sulfide and then adding a like volume. Swirl the solution for a few moments, and filter on a 15-em. 4
Lundell and Knowles. THIS JOURNAL, 17, 78 (1925).
61
paper. Acidify the filtrate with dilute hydrochloric acid (1:I), add 2 cc. in excess, and digest at 40" to 60" C. until the precipitate settles. Filter, boil the filtrate until hydrogen sulfide is expelled, and clarify the solution by small additions of nitric acid if suspended sulfur is present. Evaporate the solution to 20 to 30 cc. and filter if the solution is not clear. Add 10 cc. of 36 per cent acetic acid, 5 cc. of a 0.2 per cent solution of the aurin tricarboxylic acid,5 and finally a 10 per cent solution of ammonium carbonate in dilute ammonium hydroxide (1:2) slowly and with stirring until an excess of 5 to 10 cc. is present. Avoid a large excess. Compare the color of the solution or the amount of separated lake with the results of tests of like material containing known amounts of aluminium. Method 11-Single Filtration after Precipitation with Sodium Hydroxide-Sulfide
Dissolve the alloy as in Method I, add 50 cc. of 8 per cent sodium hydroxide solution, heat to boiling, and boil for 1 minute. Add 8 per cent sodium sulfide solution in accordance with the material under test, swirl the solution for a few minutes, and filter. Add 15 cc. of acetic acid, 5 cc. of a 0.2 per cent solution of the dye, and then ammonium hydroxidecarbonate as in Method I. More or less precipitate other than the aluminium lake may separate in the final test, but such precipitated matter should be white if a correct amount of sodium sulfide was added and should not obscure the color of the aluminium lake in alloys containing no more than 10 per cent of tin or 25 per cent of lead. Desirable additions of the sodium sulfide solution are: 0.5 cc. for tin-base bearing metal, 1 cc. for spelter, cast bronze, and phosphor bronze, 2 cc. for brass and journal bearing, and 4 cc. for lead-base bearing metal. Method 111-Single
Filtration after Precipitation with Sodium Hydroxide
Proceed as in Method 11, but omit the addition of sodium sulfide. As in Method 11, more or less white precipitate of tin and lead can be expected in the final test; this does not cause much trouble in brasses, bronzes, and journal bearings. With lead and tin-base bearing metals the method is not entirely satisfactory because the final precipitate is quite large. The method is not so certain for spelter as is Method 11,because so little precipitate is formed by the sodium hydroxide alone that the precipitation of iron is sometimes incomplete. The results given in Table I indicate which method is the most suitable for a given type of alloy. Table I (Numbers refer to Bureau of Standards standard samples) Per cent AI
present or added 0.003 0.006 Brass 37b 0.003 0.006 Bronze 52 0.003 0.01 Phosphor bronze 63 0.04 Journal bearing 0.003 0.01 Lead-base bearing 0.003 0.006 metal 53 0.01 Tin-base bearing 0.003 ' 0.006 metal 54 0.01
MATERIAL Spelter
CHARACTZR OF THE TEST OBTAINED IN: Method I Method I1 Method I11 Excellent Good . . . Excellent Good Excellent Good Good Excellent Good Good Excellent Weak Weak Fair Excellent Good Excellent Good Fair Excellent Good Fair Excellent Good Fair Excellent Unsatisfactory Unsatisfactory Excellent Very weak Very weak Fair Weak Good Unsatisfactory Unsatisfactory Good Unsatisfactory Unsatisfactory Very weak Very weak
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The reagent used in the tests was obtained from R. P. Cargille, 74 Cortlandt St.. New York City. 6
In cooperation with the Pacific Coast Gas Research Council, the Bureau of Mines is making a study of the feasibility of utilizing coals available on the West Coast for manufacture of city gas.
