DECEMBER, 1935
INDUSTRIAL AND ENGINEERING CHEMISTRY
Suppose a solid body is embedded in asphalt at the interface against water. I n order to bring the solicl from the asphalt into the water, a certain amount of energy is required. This energy is directed against the interfacial energies and, according to Hofmann (5),is equal to: S solid/asphalt - S solid/water - S asphalt/water where S denoted the interfacial energy and the suffixes the interfaces. This reaction involves two possibilities : 1. The energy is zero or positive; the solid goes freely from the asphalt into the water, since energy -. is not required or is gained-in this reaction. 2. The energy is negative; the solid remains in the asphalt and energy is required to bring it from the asphalt into the water phase. This energy is positive when the mixtures of asphalt and silica come in contact with water. The water displaces the asphalts from silica in accordance with the theory. On account of the negative values for the interfacial tensions between the asphalts investigated and limestone and blue clay, the displacing energy is negative, and water does not displace the asphalts from these aggregates. Thus with the methods outlined to measure the changes
Action of Dilute Acids on Aluminum CHARLES F. POE, R. M. WARNOCK, AND A. P. W Y S s University of Colorado, Boulder, Colo.
T
HE amount of aluminum dissolved when
foods have been cooked in aluminum utensils is a subject of more or less controversy. The degree to which aluminum cooking utensils would contribute to the presence of aluminum in prepared foods would depend upon the aluminum-dissolving substances, such a3 acids, which are present in the foods. The literature, however, reveals that very few quantitative results have been recorded concerning the solubility of aluminum in acids. The present paper reports the action of acids on aluminum, including some of those acids which may occur in food products. Some work has been done on the effects of inorganic acids and a few organic acids on aluminum. Most of this work has been qualitative, and the results are somewhat contradictory. S o attempt will be made to include here all of the references to the solubility of aluminum in inorganic acids, but the more important quantitative results with the organic acids will be listed. Of the organic acids, acetic has been most studied. Hodges (5) found that strong tartaric, citric, and previously boiled
1505
in energy which occur when asphalt comes in contact with mineral aggregate, it is possible to make predictions with regard to the behavior of asphalt paving mixtures on the road.
Acknowledgment The author desires to express his thanks to the directors of Imperial Oil Limited for the privilege of presenting this paper.
Literature Cited (1) Bartell, F.E.,a n d Jennings, H. P., J . Phys. Chem., 38,499(1934). (2) Bartell, F. E., a n d Miller, F. L , LND. ENG.CHEM., 20,738 (1928). (3) Bartell, F. E. a n d Osterhof, H. J., J . Phys. Chem., 37,549 (1933). (4) Coleman a n d G a r d n e r , Paint Mfra.' Assoc. U.S., Tech. Circ. 85 (1914). (5) H o f m a n n , F. B., 2. physik. Chem., 83,385 (1913). (6) Nellensteyn, F. J., a n d R o o d e n b u r g , N. M . , Kolloidchem. Beiheftc, 31, 434 (1930). (7) Nicholson, V., Proc. Assoc. Asphalt Paving Technolog., 1932, 28. (8) Riedel, W., a n d W e b e r , H., Asphalt Teer Strassenhuutech., 33,677 (1933). RECEIVEDMay 22, 1935. Presented before the Division of Petroleum Chemistry a t the 89th Meeting of the American Chemical Society, New York, N. Y . , Spril22 to 26, 1935.
acetic acids had no effect upon aluminum, but that cold saturated oxalic acid dissolved it rapidly. Seligman and Williams (18) studied the effect of several concentrated organic acids on aluminum and found their action to be slight. Maass and Wiederholt (11) found that the common inorganic acids had more effect on aluminum than did oxalic, acetic, or tartaric acids. Utz (19) stated that dilute lactic acid (0.5 to 1.0 per cent) had no effect on aluminum a t room temperature, and that a slight amount was dissolved a t higher temperatures, but not enough to produce any harm physiologically. Lunge and Schmid (10) and Lunge (9) studied the solubility of this metal in a few organic acids, and found the maximum amount dissolving in 6 days to be 6.35 mg. per 100 sq. cm. of surface exposed. Rupp (17') tested six organic acids during 8 days and found the maximum amount of aluminum dissolved to be 1 mg. The strengths of the acids ranged from 0.4 to 10 per cent. One per cent acetic acid dissolved no aluminuni. but 10 per cent acetic dissolved 0.1 mg. Hunziker, Cordes, and %sen (6) treated sheets (5.28 square inches) of aluminum for 5 days a t 70" F. with acetic, butyric, lactic, and citric acid3. The acids were 1 per cent except citric which was 0.2 per cent. The maximum amount dissolved was 2.1 mg. Klut ( 7 ) stat'es that aluminum is not attacked by dilute organic acids, sulfuric acid, or nitric acid. Ohlmciller and Heise (16), Plagge and Lebbin (If?),and Mansfeld (IS) concluded that aluminum was quite insoluble in cold dilute acetic acid, and somewhst soluble in the boiling acid. A number of authors (1-4,8,18, 14) have studied the action of certain acid foods on aluminum cooking utensils.
Procedure The purest sheet aluminum obtainable W:LS used and was composed of the following: alurniuum, 99.26 per cent; ircln, 0.53; copper, 0.03; silicon, 0.16; and manganese, 0.00. The aluminum was not heat-trea,ted. The strengths of the acids were normal, 0.1 normal, and 0.01 normal. Because of the insolubility of some of the organic acids, stronger solutions of them could not be prepared. One hundred cubic centimeters of each acid were measured into Pyrex flasks, and a piece of sheet aluminum (6 X 6 cm.) weighing about 4 grams was added. This sheet was allowed t o remain in contact with the solution a t 25" C. for 12 weeks, and was removed, washed, dried, end weighed at stated intervals. The loss in weight was recorded
INDUSTRIAL AND EN(31NEERING CHEMISTRY
1506 TABLE
I.
ALVVISUM IN 0.1 YORMAL ACIDS, BOILED30 MINUTESDAILY
LOSS IN WEIGHT O F SHEET
7 -
Acid Acetic Aconitic Adipic Boric Butyric Citric Formic Glutamic Glutaric Glycolic Hydrobromic Hydrochloric Hydriodic Lactic Maleic Malic Malonic Mandelic Monochloroacetic Nitric Oxalic Phosphoric Propjopic Succinic Sulfuric Sulfurous Tannic Tartaric Trichloroacetic Water (distd.)
2 weeks 525 74 + 9
iii
101 819 8 18 310 1285 1366 251 288 112 123 275 92 486 700 370 169 15 + 9 378 152 24 128 3067
..
Lose, hlg. per 100 Sq. Cm-. 4 6 8 10 aeeks weeks ueeks weeks 1106 1748 2002 2257 112 134 168 151 +14 +20 +22 +22 490 259 1160 20 18 686 1499 1583 266 610 164 250 290 124 1060 787 385 181 90
+ 7
412 160 27 260 4467
..
583 386 1535 34 15 1021 1743 1749 272 1064 209 366 314 128 1712 832 393 194 151 f 14 473 161 27 415 5765
..
xi7 392 1910 56 15 1111 1986 1933 277 1503 230 417 324 146 1816 857 398 197 278
994 431 2134 168 11 1184 2159 2087 280 1649 242 448 325 158 1905 888 404 218 448 20 546 170 38 468 7779
+
+52 164 34 449 6796
12 weeks 2425 224 +24 1024 437 2316 322 10 1201 2236 2115 292 1836 246 479 329 256 2309 913 427 212 552 19 571 176 44 491 8568
+
..
,.
ALUMINUMIN NORMAL TABLE 11. Loss IN WEIGHTOF SHEET -4CIDS AT 25" c. 7 -
Acid Bcetic Aconitic Boric (satd.) Citric Formic Hydrobromic Hydrochloric Hydriodic Lactip .Maleic Malic Malonic Monochloroacetic Nitric Oxalio Phosphoric Propjonic Succinic Sulfuric Sulfurous Tartaric Trichloroacetic Water (distd.)
2 weeks 53 52 5 6 125 1954 4204 946 59 40 46 89 1517 2363 626 1339 26 24 1001 280 31 1260
..
Loss, hlg. per 100 Sq. Cm.4 weeks 6 weeks 8 weeks 12 weeks 137 170 263 89 141 61 65 102 5 5 6 8 37 22 50 84 812 396 929 247 4334 7834 3119 5267 6415 5238 7358 9752 2349 2177 2279 1797 180 150 108 104 62 85 124 254 198 230 292 488 150 1814 1928 2214 1669 3694 5376 5658 6009 1750 2103 2467 1190 1493 1493 1493 1451 62 99 50 36 .~ 41 64 78 98 1639 2166 2393 2913 280 280 280 276 80 141 99 59 1680 2006 3046 2610
..
..
..
..
and reported in milligrams on the basis of a sheet of aluminum 10 X 10 em. With the 0.1 normal solutions, another set was run for the 12-week period, and each was boiled 30 minutes a day, a reflux condenser being used to prevent evaporation. In addition to determining the loss of weight in the aluminum strips, the amount of aluminum dissolved was also determined at the end of the second week. A number of cooking utensils representing various brands of aluminum ware were selected, and these vere tested with various acids. Two hundred cubic centimeters of the 0.1 normal acid were allorved to simmer in the untensil for 5 hours. The volume was adjusted with distilled water from time to time and the aluminum dissolved was determined in a given portion, The results are expressed in milligrams of the metal dissolved for each 100 sq. em. of surface exposed to the acid.
Loss in Weight of Aluminum Table I gives results when sheet aluminum was treated with 0.1 normal acids and boiled 30 minutes each day for 12 weeks. The amount of aluminum dissolved a t end of 2 weeks \vas also determined in a given amount of solution. These results are not here recorded since they checked closely with loss in weight. Table I shows that trichloroacetic was the most active acid tested, causing a loss of 8568 mg. of aluminurn in 12 weeks. Other acids, showing a loss of over 1000 mg., in order of their activity, were acetic, formic, monochloroacetic, hydrobromic, hydrochloric, lactic, glycolic, and butyric. Boric showed no solvent action, whereas glutaric and tannic showed very little.
TABLE111. Loss Acid Acetic Aconitic Bdipic Boric Butyric Cinnamic Citric Formic Glutamic Wutarjc Glycolic Hydrobromic Hydrochloric Hydriodic Lactic Maleic Malic Malonic Mandelic .Monochloroacetic Nitric Oxalic Phosphoric Propionic Succinic Sulfuric Sulfurous Tannic Tartaric Trichloroacetic Water (distd.)
TABLE IV. Loss
IN WEIGHTOF SHEETALUMINUMIN NORMAL ACIDShT 25"
c.
-Loss, 2 weeks 36 12
66 24 16
95 35 17
176 42 23
22 I 12 86 13 8 56 435 755 222 60 31 28 87 19 85 488 280 116 28 12 266 98 10 27 1127
41 2 24 149 46 10 130 1074 1238 240 107 55 56 126 43 150 548 289 134 38 18 351 116 13 51 1540
85 + 2 30 252 47
1% + 2 43 319 52 9 200 1353 1440 356 184 89 110 214 72 226 587 291 128 92 35 374 113 26 90 2150
..
0.1
hIg. per 100 S q . Cm.4 weeks 6 weeks 8 weeks 12 weeks
8
..
..
8
155 1301 1340 280 150 75 80 186 61 193 572 290 131 61 27 373 110 19 19;:
..
..
192 63 34
202 '6; 557 62 9 318 1521 1522 478 262 122 132 23 1 81 376 684 286 126 106
-45 403 106 42 154 2690
..
IN WEIGHTOF SHEET ALUMIXUMIN 0.01 NORMAL ACIDSAT 25" C. 7 -
Acid Acetic Aconitic Adipic Ant hrapilic Aspartic Benaoic Boric Butyric Cinnamic Citric Formic Glutamic Glutaric Glycolic Hydriodic Hydrobromic HydTochloric Lactic Maleic Malic Malonic Mandelic Monochloroacetic Nitric a-Xitrobenzoic Oxalic Phosphoric Picric Propionic Salicylic Succinic Sulfuric Sulfurous Tannic Tartaric Trichloroacetic Water (distd.)
VOL. 27, NO. 12
2 weeks
Loss, M g . per 100 Sq. Cm-. 4 weeks 6 weeks 8 weeks 12 weeka 61 17 15 6 10 18
43 10 15 6 4 15
..
17 4-6 32 54 10 12 48 102 57 67 61 18 18 16 40 38 34 20 15 14 11 18 38 12 17 12 9 29 5
..
..
21
+
290
14 17 87 113 87 97 120 32 26 20 64 61 46 20 15 16 13 22 44 28 19 21 18 32 8
..
69 18 l8 9
21 lo
..
27 + 39 21
90 12 18 112 139 105 115 155 32 37 20 81 87 59 23 15 17 13 27 49 30 22 12 18 36 8
..
77 18 20 9 10 21
100 18 18 9 10 21
35
+ 453921
+
106 14 19 114 167 133 123 174 35 40 20 100 95 70 24 15 17 16 33 51 31 21
12 40 38 14
..
..
124 14 19 112 192 189 162 197 38 40 25 140 128 98 23 15 17 22 42 51 42 21 11 40 36 22
In succinic and adipic acids, the sheets gained in weight. Aluminum allowed to stand in contact with distilled water showed no change in weight. The loss in weight of the aluminum sheets is affected by many factors, such as time, amount of acid, presence of impurities, mechanical losing of emall particles, etc. Also an oxidation may occur on the surface of the metal which will retard the solubility and even cause a gain in weight. Table I1 gives the results when normal acids were allowed to stand in contact with the metal a t 25" C. Hydrochloric acid was the most active, causing a loss of 9752 mg. Other acids showing a loss of more than 1000 mg. were hydrobromic, nitric, trichloroacetic, sulfuric, oxalic, hydriodic, monochloroacetic, aiid phosphoric. The least active acids were boric, citric, succinic, and propionic. Table I11 shows the results when the aluminum was treated Tvith 0.1 normal solutions a t 25' C. gcid of this strength was
DECEMBER, 1935 TABLE
V. Loss
IN
INDUSTRIAL AKD ENGIKEERING CHEMISTRY
WEIGHTOF SHEET ALUMIXUM IN 0.1 NORMAL ACIDS AT
Bcetic Citric, Formic Glycolic Hydrobromic Hydrochloric Hydriodic Lactic blaleic Malic Malonic Nit+ Monochloroacetic Oxalic Phosphoric Sulfuric Sulfurous Tartaric Trichloroacetic
TABLE VI.
day 2 0.7 4 12 24 38 5 43 0.5 0.8 13 45 9 36 58 29 35 5 439
LOSS IS
25"
c.
Loss, Mg. per 100 Sq.Cm-.days 14 days days 7 days days 28 43 15 21 8 4 lo 3 l1 16 9 20 36 48 16 25 36 41 65 99 161 108 415 105 180 255 550 728
7 -
dcid
%
!g
1 ;
;:1
3 3 37
3 6 43
2A:
5 8 56
9 17 73
210 136 213 1:s 858
lgi
lii
2iE 4Tt
70 82 67
113 128 118 1 ;: 709
152 132 143 ;:1 760
,ki
600
zii 26 24 96
4:i
264 125 240 1:; 1138
WEIGHTOF SHEET ALUMINCM IK 0.1 NORM.4L BOILED30 hlINUTES DAILY
*4CIDS,
_-__day
Acid Acetic Citric Formic Glycolic Hydrobromic Hydrochloric Hydriodic Lactic Maleic
-
7 48 23
95 108 64 "3
Loss, days 5l 11 152 41 327 386 209 47 7
JIg. per 100 Sq. CIn. days days lo days I? day; 118 212 580 583 53 96 25 27 260 360 523 793 108 146 208 296 1340 915 1228 608 1108 1366 629 844 229 241 260 267 86 125 177 262 28 33 53 89
1507
given in the preceding tables, additional tests were run for shorter periods with the most active acids. Table V gives the results when 0.1 normal acids were allowed to remain in cont'act with aluminum for 1 , 3 , 5 , 6 , 10, and 14 daSs at 25" C. Some acids had lit& or no effect for the first few days, whereas others began their activity at once. Table VI lists the results for the first 2 weeks when the aluminum sheet's were heated to boiling in the solutions of 0.1 normal acids for 30 minutes each day. Table VI1 records the test on aluminum cooking utensils with certain common acids, a number of which are found in foods. Each brand of aluminum is designated by letter. C and F are die-cast aluminum, and the others are spun aluminum. Taking the average relative activity of each 0.1 normal acid, they rank in order of dissolving power as follows: Lactic, acetic, glycolic, tartaric, malic, phosphoric, citric, propionic. There is no uniformity as to rate of dissolution of a given acid of different utensils. Die-cast utensils c and F were acted on to a greater degree; this may be due to the more porous condition of the surface and the presence of other elements in the aluminum. I n two cases the solubility was less in normal than in 0.1 normal acetic acid.
Discussion
Of the inorganic acids, the halogen acids seem most active. Of the organic acids, acetic and its chlorine derivatire3, 203 273 437 formic, and lactic are rather active. d number of acids 145 388 652 698 71.1 740 388 388 showed a rather great, dctivity for the first few weeks, but 383 385 iai 342 thereafter decreased. h n o n g the.;e are glycolic: hydrio!i i:i 50 112 124 140 Sulfurous 148 152 dic, malonic, oxalic, sulfurous, etc. The metal may have Tartaric 5 2b 38 54 88 113 28.15 3186 become coated with a fine film of the aluminum salt and 829 20045 2320 2519 Trichloroacetic t h u s m a d e f u r t h e r solution difficult. Most of the acids found in fruits and vegetables are more TABLE VII. EFFECT OF ACIDSo s ALLXISEVCOOKISG UTESSILS or less active on aluminum. For this reason it MK.of .kl Dissolved per 100 Sq.CIn. of Surface Exposed to Acid might be expected that acid food would dissolve A,.. per .kcid A B C' D E F some aluminum during the cooking process. It 0.1 N h' acetic 'f&t "3;:; l:: cannot, be said at, present, however, how much the 0 . 1 N citric 2.4 49 1 172.8 6.5 32.4 31.7 41.1 48.1 solubility of aluminum uvx1ld be altered by t,he 0.1 h'glycoiic 40.5 27 .3 272.3 44.5 1 1 5 . 1 162.3 98.4 108.6 0 . 1 N lactic 40 3 89 i 3 3 4 . 9 49.7 131.8 201.8 121.0 137.4 other constituents of foods. 0 ., 1 o l N phosphqric malic $,,: :;:$ !$: !!;: Sothing stated in this paper should be construed 0 . 1 Npropionic 21.4 , .9 29 6 45 5 33.9 16 9 21.2 25.2 as claiming that aluminum i,j not :h proper ma0.1 N tartaric 13 5 28 l 140.4 47.5 49 7 86.5 67.0 61.8 Water (distd.) 5.7 3.3 2.2 2.2 2.4 4.3 2.2 3.5 terial for use in the manufacture of cooking utensils. The physiological action of aluminum salts has not been considered. found to be less active a t 25' C. than when the 5olutions and Literature Cited sheets of aluminum were heated each day (Table I). Adipic, succinic, and hydriodic acids were the exception$. The ordi(1) ~ ~ G , ~B,, unangSt, 1 , R, B., wigman,€1, B,, and (-ox, G , , I , , nary mineral acids showed the greatest activity with the exISD. ESG. CHEW.,24, 405 (1932). ( 2 ) C h i a r i a , P., Giorn. f a r m . chim., 78, 530, 533 (1929). ception of trichloroacetic. Acetic, formic, and rnonochloro(3) Fellenberg, V O n , Deut. Aert.e-Zeitun!3. 6 , NO. 253 (19311. acetic acids showed much less action at 250 C. than did the (4) Fillinper, F r a n a von, 2. ,Vuhr. Genussm., 16, 232 (1908). mineral acids. Tartaric acid showed slightly more loss of &&es, E, R.,them. .Vews, 119, 64 ( 1 9 1 9 ) ; 121, 178 (1920) ; metal wit,h 0.1 normal acids than with normal acids, 123. 141 (1921). (6) Huna'iker, 0'. F., Cordes, SV. H., and Nissen, B. E.. J . Dairy Sei., Table IV gives the results when 0.01 normal acids were 12, 140 (1929). used and allowed to act 11-ith the aluminum a t 25" C. As (7) Klut, H., Korrosion u. Metallschutz, 1, 232 (1925). with the two higher strengths of acids, the halogen acids were (8) L e h m a n n , K. B., Arch. Hug. Bakt., 102, 349 (19291. found to be the most active as a class, but the order is re(9) L u n g e , G., Chenz. ,Yews,65, 110 (1892). (10) L u n g e , G., and S c h m i d , E., 2. angew. Chem., 5 , 7 (1892). versed, hydriodic being the strongest and hydrochloric the (11) Maass, E., and W i e d e r h o l t , IT'., 2. Metallkunde, 17, 115 (1925) Feakest. Of all the acids tested in 0.01 normal solutions, (12) M a k u s h e n k o , M. I., Tmetnuie MetaL, 1930, 348. lactic was the most active, but mandelic and glycolic acids (13) Mansfeld, M., 2. rntersuch. AVahrunga- Geitussm., 8, 76:) gave rather surprisingly high results. Cinnamic acid showed (1904). (14) Mrak. E. h'l., a n d Criiess, K. V., Food Ind.. 1, 559 (1929). an increase in weight. Most of the acids showed greater (15) Ohlmdller, W., a n d Heise, R., A r b . kais. Gesundh., 8, 377 activity as the strength of the individual acid increased. The (1893). results, however, for lactic acid were about the same for all (16) Plagge, Sv.,a n d L e b b i n , G., Veragg. geb. .~~ilitar-Sanitats~,esens. three strengths of acid. A number of the acids gave approxi3, 1 (1893). (17) Rupp, G., Dingier's polyiech. .J., 283, 19 (1892). mately the same results a t the end of 12 weeks as they did (18) Seligman, R., a n d Williarn3, P.. J . Soc. Che n. I n i . , 33, 83 ,1916). at the end of 2 weeks. (19) Utz, 2. angew. Chem., 32 ( l ) ,346 (1919). Because the question might be raised that foods do not remain in contact with the aluminum for the periods of time R E C ~ I V EApril D 15, 1935. 4
4i 26
Malic Malonic Monochloroacetic Nit+ Oxalic Sulfuric Phosphoric
&, 122
2ii 2i: 177
2::
::A
iiy
",:::,$:;
3:;
ii:;
i:
;::,:
8f,i
