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Vol. 17, No. 1
INDUSTRIAL AND ENGINEERING CHEMISTRY
cows that produced the butter fats under consideration originated from carefully developed stock, and without doubt had received better care and rations than are given to the average dairy cow. No attempt should be made to compare the vitamin potency of the butter fats produced by the different breeds, since the age, feeding, period of lactation, and number of lactations were not identical for the cows of the differs n t breeds. In fact, considerable study of these factors will
be required in order to obtain definite information concerning the vitamin potency of average dairy butter. Acknowledgment
The author wishes to express his appreciation to Mason Garfield, The Dodge Brothers, John Gifford,and the American Woolen Company for supplying the milks from which the butter fats under consideration were obtained.
Determination of Aluminium in Nonferrous Alloys' .
By G. E. F. Lundell and H. B. Knowles BUREAUOF
STANDARDS, WASHINGTON,
D.c.
HE only difficulty in determining aluminium in non- is rapid, it enables the analyst to see the aluminium, and it is ferrous alloys lies in the number of operations that are quite accurate for a method of this type. It is not intend3d necessary. The usual preliminary separations leave that the method shall replace the longer and more accurate iron still associated with aluminium, and it is then necessary phenylhydrazine method, although in ordinary hands there either to separate it by precipitation with sodium hydroxide is not much choice between the two. Briefly stated, copper, zinc, lead, iron, nickel, manganese, or else to separate the aluminium by precipitation with phenylhydrazine after reduction of the iron. The practice of and similar elements are separated by filtration after precipiweighing iron and aluminium totation with sodium sulfide, and tin, gether and calculating aluminium antimony, arsenic, and any other A method for the determination of aluelements of the arsenic group are by difference after determining the minium in nonferrous alloys is described in iron is not entirely satisfactory next eliminated by acidification of which the usual alloying elements except when careful work is done and is the filtrate and a second filtration. phosphorus are separated from aluminium a dubious procedure at best when These operations leave aluminium by first precipitating with sodium sulfide but a 0.1 or 0.01 per cent of aluminas the only possible remaining conreagent and filtering, and then acidifying ium is in question. This is evident stituent in ordinary nonferrous the filtrate and again filtering. The prowhen one considers that nitric acid materials, and its absence is assured cedure is recommended for routine analysis digestions do not always remove all if no precipitate is subsequently and is not intended to replace the longer and obtained with the treatment more accurate phenylhydrazine method. other hand, a isOn almost with that sulfuric acid mayOr not remove all lead, that these are precipitated sure evidence of aluminium if the by ammonia unless previously removed by hydrogen sulfide, reagents are free from this eIement, and the only ordinary that manganese and particularly zinc contaminate the am- contaminant is silica. Phosphorus, if present in the alloy, monia precipitate unless special precautions are taken, and will come down with the precipitate, as would &o a few that determinations of iron are seldom accurate to 0.01 per elements like vanadium and glucinum which are not expected in this material. cent and are often in much greater error. The direct precipitation of aluminium by the addition of Preparation of Solutions an excess of ammonia to a solution of the alloy is not desirable, because aluminium hydroxide is appreciably soluble in SODIUM HYDROXIDE SOLUTION (2.5 PER CENT)-Dissdve 25 $he excess of ammonium hydroxide which must be used to grams of sodium hydroxide (free from aluminium) in water and keep copper and zinc in solution. Moreover, the precipi- d i $ ~ ~ ~ ~ ~SoLuTIoN--Dissolve o ~ ~ ~ ~ ; D E150 grams of sodium tation but a p r e h i n a r y One, as the Precipitate will contain hydroxide (free from aluminium) in 1000 cc. of water, saturate all the tin and iron, nearly all the lead, and more or less 500 cc. of this solution with hydrogen sulfide, and mix with the remaining 500 cc. of solution. copper, zinc, manganese, and nickel. The use of solutions of sodium hydroxide or sodium sulfide Of hydrochlois not in good repute among analysts, and it is with hesitation A ~ I H~~~~~~~ ~ ~ ~sULPIDE ~ E WATER-Dilute ~ 10 cc. of bythat the authors propose a method in which a solution contain- drochloric acid (specific gravity 1.19) with 1000 cc. of water and ing these reagents is employed. Part of the prejudice against saturate the solution with hydrogen sulfide. CHLORIDESOLUTION (2 PER CENT)-Mix 30 CC. is caused by the be- of AMMONIUM the use Of the alkaline hydrochloric acid (specific gravity 1.19) with 200 cc. of water, havior of filters during filtration and washing, and Part by the add methyl red, neutralize with ammonia until the solution impure character of the reagents furnished in the past. These changes to a distinct yellow, and then dilute to loo0 cc. with objections do not carry much weight in the proposed method, water. because sodium hydroxide that is free from aluminium can Procedure now be obtained, and the filtration is simplified because only a part of a clear supernatant solution is filtered through a Dissolve 2 grams of the sample in 20 cc. of hydrocMoric acid (specific gravity 1.19) and 5 cc. of nitric acid (specific large filter and no washing is required. Having recounted the unattractive features of the method gravity 1.42). Boil the solution to expel chlorine and dilute it can now be said that it possesses enough desirable qualities with 50 cc. of water. Nearly neutralize the cold solution with to warrant its consideration for use in routine analysis. It sodium hydroxide solution (2.5 per cent, or stronger if much free acid is present), and pour it slOwly and with con;rtant Published by permission of the Director, 1 Received August 4, 1924. shaking into a 500-cc. volumetric flask containing 100 cc. of U. S. Bureau of Standards.
T
precipitati
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;z$:t
January, 1925
INDUSTRIAL A N D ENGINEERING CHEMISTRY
sodium sulfide solution. Dilute to the mark with sodium hydroxide solution (2.5 per cent) and mix thoroughly. Filter on a large, dry, No. 42 Whatman filter paper (or its equivalent) and keep the paper well filled with solution lest iron be oxidized and dissolved. Reject the first 20 to 25 CC., and catch exactly 250 cc. which will represent 1 gram of sample. I n routine analyses of material containing not more than 1 per cent of aluminium, the aliquot portion can be gathered in a 250-cc. graduate. Transfer the aliquot portion to a 600-cc. beaker, neutralize the solution with dilute hydrochloric acid (1 :3), and finally add 25 cc. in excess. Digest at 40"to 60" C. for 1 hour, filter, and wash the paper and precipitate with acidified hydrogen sulfide water. Boil the filtrate and washings to expel hydrogen sulfide, add a few drops of methyl red indicator, and then dilute ammonia (1:2) until the solution is just distinctly yellow. Boil for 1 to 2 minutes and filter at once through a small filter. Wash the beaker, paper, and precipitate two or three times with hot ammonium chloride solution (2 per cent) and discard the filtrate. Dissolve the precipitate in 20 cc. of hot dilute hydrochloric acid (1: 3 ) , wash the filter thoroughly with small portions of hot water, and reserve it for the second filtration. Dilute the filtrate to 50 cc., add methyl red, and precipitate with dilute ammonia (1 : 2) as before. Filter, wash with hot ammonium chloride solution (2 per cent), and ignite. The ignited residue is prone to carry silica and must be purified before weighing as follows: Add one or two drops of water, one drop of diluted sulfuric acid, and 1 to 5 cc. of hydrofluoric acid. Evaporate to dryness, increase the heat slowly, and finally heat with a blast lamp or its equivalent. Weigh as A1203. The weight of A l 2 0 3 corrected for the blank and multiplied by 52.94 gives the percentage of aluminium. The first aluminium hydroxide precipitate will carry down some sodium chloride and much of any silica that was dissolved in the sodium hydroxide solution; hence it is not safe to omit the second precipitation and the hydrofluoric acid treatment. There is no attack on the glassware during the short contact with the weak, cool, alkaline solution. It is, of course, preferable that the sodium hydroxide be free from aluminium. The most satisfactory test for it lies in running an analysis with nonferrous alloys containing no aluminium. Direct test, by acidification followed by precipitation with ammonia, is sufficient if no precipitate is obtained, but is of doubtful value in case one appears, for it may contain other elements, such as iron, which do not affect the results. Very little aluminium is retained by the first sulfide precipitate, or by the second precipitate except when both tin and aluminium are high. I n this special case a larger sample, say 4 grams, can be used and the tin can be precipitated by pouring the aliquot of the sodium sulfide filtrate into an excess of acid contained in a 500-cc. flask, making up to volume and taking 250 cc. of this solution. This may be a desirable variation of the method for all cases, as one could thus avoid the filtration of the whole solution and the use of hydrogen sulfide wash water. There is no need for correcting the volume of the solutions for displacement by the precipitate, for the plus error which is introduced is small and tends to compensate for a minus error caused by retention of aluminium by the precipitate. If the phosphorus is known to be present, the method should be followed through the first addition of ammonia. If aluminium is indicated, re-acidify the solution with hydrochloric acid, add macerated paper, two drops of methyl orange, and 10 cc. of a solution of diammonium phosphate (10 per cent). Render the solution just ammoniacal, then just restore the pink color with dilute hydrochloric acid (1 :3), heat
79
to boiling, and add 30 cc. of a solution of ammonium acetate (25 per cent). Boil for 5 minutes, filter on an 11-cm. No. 42 Whatman or similar filter paper, and wash with hot ammonium nitrate solution (5 per cent) until 5 cc. of the washings no longer give a test for chlorides with acidified silver nitrate. Ignite in platinum or porcelain, heat at approximately 1100" C. for 10 minutes, and weigh as AlPOd. This method is not strictly accurate on account of the uncertain composition of the phosphate, but is sufficiently accurate for all but, the most painstaking analyses. Results In Table I are given the results of analyses of various Bureau of Standards standard samples to which known weights of aluminium were added, except in the cases of Samples 62 and-63, which contain aluminium. TABLE I-DETERMINATION OB ALUMINIUM IN
ALLOYS ALUMINIUM SAMPLE Found None Sheet Brass No. 37b 0.047 2.10 Cast Bronze No. 52 None 0.074 2.09 Manganese Bronze 1.12 No. 62 1.13 1.15 Pb % ' I Sb, Bi, Cu, None Lead-Base Bearing None As 0.05 0.07 Metal No. 53 2.05 2.05 Tin-Base Bearing Sn,Sit, Cu, PS, Bi, None None Fe, As 0.05 0.06 Metal No. 54 3.05 1.970 2.05 1.910 0.04 0.039 Phosphor-Bronze Bear- Cu Sn Pb P Sb Zn, +e, tis, 5, AI, rji ing Metal No. 63 0.039 a The regular procedure was used and not the special precipitation of tin sulfide suggested in the discussion of the method. NONFERROUS
PERCBNTAGE ELEMENTS PRBSGNT Present Cu, Zn, Sn, Pb, Fe, N i None 0.05 2.05 Cu,Sn, Zn, Pb, Fe, Ni, None Sb 0.05 2.05 Cu Zn Mn Fe, Al, 1.13 Bn, h i , pi,
OF
+.e:
Tests by Other Investigators I n addition to these analyses, which were made by one of the writers, additional tests of the method were made by H. A. Buchheit, of the Bureau of Standards; J. E. Virchow, of the C. B. & Q.R. R., Aurora, Ill.; Jerome Strauss, U. S. Navy Yard, Washington, D, C.; W. F. Muehlberg, Newburgh Steel Works, Cleveland, Ohio; s.A. Weigand, Lunkenheimer Co., Cincinnati, Ohio; F. M. Barry and L. E. Lougee, Scovill Manufacturing Co., Waterbury, Conn.; J. B. Moseley, The Ajax Metal Co., Philadelphia, Pa.; W. J. Brown, The National Lead Co., Brooklyn, New York; H. A. Bedworth, American Brass Co., Waterbury, Conn.; W. E. Baulieu, Bridgeport Brass Co., Bridgeport, Conn.; and M. E. McDonnell, P. R. R. System, Altoona, Pa. The comments concerning the method were, in the main, encouraging, and the results were as follows: For Manganese Bronze No. 62, twenty-eight determinations ranged from 0.95 to 1.16 per cent and the average deviation from the certificate value (1.13 per cent) was 0.03 per cent; for Phosphor-Bronze Bearing Metal No. 63, one result of 0.18 was reported, but the remaining thirteen determinations ranged from 0.035 to 0.07, with an average deviation from the certificate value (0.04 per cent) of 0013. I n addition, one analyst obtained 9.59 per cent aluminium as against 9.62 in an aluminium bronze containing 3.5 per cent of iron, and another added 2 per cent of aluminium to samples of the bureau's nonferrous alloys, and obtained 2.07 and 2.05 for No. 37b, 2.07 and 2.05 for No. 52, and 1.88 and 1.81 in No. 54. The possibility of determining arsenic, tin, and antimony in the precipitated sulfides by some such procedure as Stief's2and determining phosphorus in an aliquot portion of the second filtrate were also suggested. $ T H I S JOURNAL,
7, 211 (1915).
