\ Vj ✓ 5 > ' M ■ \ THE CORROSION OF METALS IN DILUTE ORGANIC ACIDS BY JEAN CHARLOTTE SHEPHERD B. A. University of Montana 1919 THESIS Submitted in Partial Fulfillment of the Requirements for the Degree of MASTER OF SCIENCE IN CHEMISTRY IN THE GRADUATE SCHOOL OF THE UNIVERSITY OF ILLINOIS 1921 ■ . YbSA SVV UNIVERSITY OF ILLINOIS THE GRADUATE SCHOOL i q ?i I HEREBY RECOMMEND THAT THE THESIS PREPARED UNDER MY SUPERVISION BY JEAN CHARLOTTE STfKPtraTTT) ENTITLED TM_ 0 QRH 03 I 0 IL^^iEgi 3 X 3 III DILUTE ORO-Al TP) AJYTTjS BE ACCEPTED AS FULFILLING THIS PART OF THE REQUIREMENTS FOR THE DEGREE OF Master of Sci ence Recommendation concurred in* Committee on Final Examination* ""Required for doctor’s degree but not for master’s / 0 C ^ A\ AGJfflOVflEDGMEH T ±he autnor takes this opportunity to express her appreciation and most sincere thanks to Doctor J. H. Reedy for his valuable help and direction so kindly and freely given in this investigation. Digitized by the Internet Archive in 2015 https://archive.org/details/corrosionofmetalOOshep TABLE OF COIT TENTS I INTRODUCTION I I EXPERIMEN TAL PA RT (a) A Discussion of Methods ( b ) Apparatus ( c ) Legend III DISCUSSION ( 1 ) Gene ral (2) Propionic acid (3) Tartaric acid (4) Citric acid ( 5 ) Alanine (6) effect of Previous Treatment of Metal Page 1 3 3 5 7 7 16 25 25 38 39 IV SUMMARY V BIBLIOGRAPHY 40 1 - THE CORROSION OP LIE TALS BY DILUTE ORGANIC ACIDS I. INTRODUCTION This p ro bl era was suggested by the corrosion of milk containers used in the Dairy Department of the University. The acid concen- tration in milk varies from O.OOl H to 0.1 E, the stronger acid being found in sour milk. These aoids consist of a mixture of amino, ny roxy, and unsubstituted mono=, di-, and tricarboxylic acids, in the following experiments an attempt has been made to compare tne rate of corrosion of various metals in each type of acid. According to the electrolytic theory of corrosion advanced by Whitney 1 , iilden^, and others, every metal has a certain solution tension which differs for different metals and depends also on the pnysical state of the metal. If we immerse any metal in water, it te.ids to go into solution to form positive ions leaving the metal negatively charged. Unless we remove this negative charge from the metal, the electrostatic force between the metal and the ions soon equals the solution tension of the metal and solution will cease. If we have a crystalline metal, different parts of the crystals Will nave different solution tensions and we will have small cells formed between different parts of the metallic surface. In this oase, hydrogen will be liberated at the surface of the metal, but the h. II. I\ is so small that the hydrogen cannot escape as a gas . It polarizes the cell, and, unless it is removed by some means, corrosion will cease. Dissolved oxygen tends to combine directly with the hydrogen and therefore, if we have oxygen present, the natal will corrode until the supply of oxygen is used up. Ii we nave an impure metal, v,e have two substances of different * t . . ' . 2 - aolution tensions and we will have a corrosion cell established as before. The E. Ivl. F. in this case is somewhat larger and the hydrogen liberated may pass off as a gas. All or part of the hydrogen however, may combine with dissolved oxygen. 7 Bengough, in his work on the corrosion of brass, has defined two types of corrosion, "complete", in which all of the substances present are removed in the proportions inwhich they occur in the sample, and "selective", in which corrosion takes place at the expense of the constituent having the highest solution tension. Complete corrosion depends entirely upon dissolved oxygen and the amount of metal dissolved is directly proportional to the amount of oxygen consumed. "Dezincification described by Bengough, in the case of brass in sea water, is an example of selective corrosion and may be accompanied by the evolution of hydrogen. It is well known that strains brought about by the bending and twisting of a metal increase the rate of corrosion. Also, sharp edges and points on a surface corrode more rapidly. This compli- cates the problem of comparing the rates of corrosion of different samples because of surface differences between the pieces of metal. Temperature and the presence of even minute traces of impurities cause marked differences in the rate of corrosion. , , , c 3 - II. EXPERIMENTAL PART (a) Disoussion of Methods.- The usual method of measuring the rate of corrosion is to immerse the weighed sample in the solvent for a given length of time, usually weeks or even months, then clean hy careful washing and weigh again. In strong solution* and with large samples, the difference is easily weighable , and the loss on cleaning is negligible. However, with dilute solu- tions after only a few days time, the loss in weight is a matter of tenths of a milligram at most and the loss on cleaning becomes a larger factor in the accuracy of measurement. -ilso , in tne above method, the rate of corrosion is assumed to be a straight line function. There is no evidence to support this assumption because the composition of the solution is contin- ually changing. and many reactions of this type exhibit the phenome- non of an induction period. On the other hand, corrosion of pure metals or metals contain- ing only traces of impurities by dilute solutions, is always accom- panied by the absorption of oxygen. This, then seems to offer a means of measuring a very small loss in the sample with a higii aegree or accuracy. By using an air tight container connected to a manometer, small changes in the volume of gas can be calculated from daily readings and a true measure of rate of corrosion obtain- ed . (b) Apparatus .- A diagram of the manometer cell used is given lx: figure 1. It was found necessary to use ground glass stoppers, as rubber stoppers were not air tight under the conditions of the experiment, even when resurfaced with sealing wax and shellac. A few of the stoppers used did appear to hold a vacuum, but as a rule v t . , * . F;«I 5 - They oould not be depended upon. It may be that under a vacuum, air leaks slowly through the pores of the rubber. A spark was passed between the platinum points AA , at intervals during the course of the experiment to test for the presence of hydrogen. The mercury in the manometer showed a tendency to distil over on to the metal. This was especially noticeable in the case of copper, because the presence of the mercury on the surface of the sopper seemed to inhibit corrosion. A thin layer of ilujol was put on top of the mercury to prevent this distillation. ! The strips of metal had a uniform surface area of 17.7 sq. cm. The dimensions were not exactly the same in each case, because the metals could not be obtained in sheets of the same thickness. The strips were all very thin, however, in comparison to the length and width. The volume of the solution was the same in each case (50 cc ) and as the manometer cells we re of practically the same volume, the volume of oxygen present in each case was very nearly the same. The manometer cells , when filled were placed- on a shaking machine having a gentle horizontal motion in order to keep the solution saturated with oxygen. Due to the complicated nature of the apparatus and its conse- quent limited supply, all the experiments could not be run at the same time under exactly the same conditions. In this respect, the results are not strictly comparable. In order to make daily read- ings independent of volume changes due to temperature and atmos- pheric pressure, a blank was run using a manometer cell of the same size as the others containing 50 cc. of water. (c) legend.- In all of the following ta'oles, the time is given in days, D x represents the daily difference in level of raer- 6 - cury for the first sample, Dg , the difference in the secoiid sample, and C the difference for the manometer cell run as a blank. The number of units equivalent to one cc . of oxygen in each case is given at the bottom of the column. For G in all cases 1 cc. Or, is equivalent to 10.4. The results are expressed in cc . of oxygen absorbed . Each of the following graphs represents a series of experiments run at the same time, under the same conditions. 7 - III. DISGUSSIOH OF RESULTS. (a) General.- In looking over the data, there are two points thatstrike one rather forcibly. In the first place, none of the curves are straight lines. In other words, if a sample loses 0.5 grams in 5 days , we are not justified in assuming that it lost 0.1 gram the first day. In most cases the reaction was ran id lor the first day or two, gradually falling off to zero. ( Platesl3 ,14) In Plates 3,4, however, we have evidence of a marked period of induction. In the second place, there is a wide variation in the results obtained in the two samples run as checks. In general, the two curves obtained are of the same shape, but it is impossible to obtain the same absolute values. The main source of this dis- crepancy is the difference in condition of the two metallic sur- faces. Ko amount of polishing can bring them to exactly the same state. While the values obtained are not absolute, they are good enough to enable us to draw certain conclusions, concerning the action of an acid on varioiis metals. (b) Propionic Acid (Table I, II, III, IT; Plates I, II, III, IV I The rates of corrosion of copper, tin, zinc, and aluminum are what we would expect from considerations given in the first part of this paper. In general, the rate is dependent on the solution tension of the metal and the hydrogen ion concentration of the solution. The data given indicate that copper corrodes more rapidly than tin, but in tne case of copper, the corrosion product was soluble while in the case of tin, a white precipitate settle^ p n the surface oi tne metal. This may account for the apparent contradiction to the general rule. The precipitate in normal acid was much heavier . « * - - • t r r C t f . r * Copper in Propionic Acid N Days C D cc . 0 0 0.00 0.58 0.000 1 0.13 1.69 0.049 3 -1.05 3.21 0.245 5 - 1.85 4.37 0.389 7 -£.26 5.91 0.515 9 -1.93 7.65 1 cc=crl8. 11/ 10 0.579 0 0.00 1.0C 0.000 1 0.15 2.38 0.092 3 -1.05 3.00 0.265 5 -1.85 4.21 0.419 7 -2.26 5.40 0.551 9 -1.93 7.23 1 cc^xL3.2 11 / 100 0.669 0 0.00 0.60 0.000 1 0.13 0.81 0.009 3 -1.05 0.20 0.071 5 -1.85 - 0.09 0.143 7 -2.26 0.18 0.188 9 -1.93 0.39 1 cc<^15 K/1000 0.171 0 0.00 C.36 0.000 1 0.13 1.25 0.054 3 -1.05 0.30 0.094 5 -1.85 - 0.49 0.104 7 - 2.26 -1.02 0.104 9 - 1.95 - 0.54 1 ccci3.2 0.117 9 - xin in Propionic Acid E Days G D 0 0.00 0.60 1 0.15 1.65 n -1.05 1.76 5 - 1.85 1 . 65 7 - 2.26 2.75 9 - 1.95 5.50 1 ccc^15. 6 N/10 0 0.00 0.92 1 0.15 2.15 5 - 1.04 2.90 5 - 1.85 5.52 7 - 2.26 5.99 9 - 1.95 5.20 1 cc=0=-18.0 H/100 0 0.00 0.50 1 0.15 0.95 5 - 1.05 0.50 5 - 1.85 - 0.46 7 - 2.26 -0.72 9 -1.95 -0.50 1 0CO18.4 H/1000 0 0.00 0.71 1 0.15 1.08 5 -1.05 0.21 5 -1.84 r- 0.67 7 -2.26 - 0.87 9 -1.95 - 0.28 1 cc =c=l 5 . 0 cc . 0 2 0.000 0.064 0.186 0.254 0.574 0.584 0.000 0.080 0 . 247 0.547 0.445 0.501 0.000 0.012 0.087 0.126 0.150 0.142 0.0C0 0.008 0.071 0.102 0.1.25 0.125 Aluminum in Prop ionic Acid. H Days C D oc . 0 0 0.00 0.49 0.000 1 0.13 1.20 0.055 3 -1.05 2.00 0.241 5 -1.85 2.79 0.385 7 -2.26 4.33 0.580 9 -1.93 6.07 0.615 1 cc=0=10.6 11/10 0 0.00 0.44 0.000 1 0.13 1.63 0 • 062 3 - 1.05 2.77 0.238 5 - 1.85 3 . 59 0.258 7 - 2.26 4.61 0.476 9 - 1.93 6.69 0.558 1 CCCrl6.ffi 11/100 0 0.00 0.42 0.000 1 0.13 2.14 0.086 3 - 1.05 3.45 0.266 5 -1.85 3.84 0.378 7 - 2. £6 4.67 0.454 9 -1.93 5.90 0.500 1 GCr0rl8 H/1000 0 0.00 0.46 0 . OOC 1 0.13 1.03 0.025 3 -1.05 0.39 0.092 5 -1.85 -0.22 0.161 7 — 2.26 0.06 0.189 9 - 1.93 0.20 C .167 1 ccrC=15 11 - Zinc in Propionic Acid H/lOO Pays C D cc . 0 0 0.00 0.82 0.000 1 0.13 2.14 0.059 3 -1.05 2.90 0.212 5 -1.85 2.70 0.281 7 -2.26 2.69 0.319 9 - 1.93 3.55 0.334 1 CC18 K /100 0.000 - 0.35 0.019 0.44 0.054 1.31 0.084 1.52 0.125 1.45 C .140 2.25 0.155 2.27 0.160 3.89 0.224 4.32 1 cc = c = 13.2 K/1000 0.000 0.37 0.034 1.01 - 0.044 2.76 - 0.038 3.05 - 0.007 2.02 - r - 0.041 3.37 - 0.017 2.71 1 CC=OlQ GG 0 0 0 0 0 0 0 0 0 0 - 0 - 0 - 0 - 0 c - 0 0 0 0 0 0 0 0 0 0 0 . 0 . - 0 . - 0 . - 0 . - 0 . - 0 . .000 .000 . 023 .045 .082 .094 .113 .1005 .143 .000 .015 .1706 .1398 .1192 .0144 023 000 029 095 123 171 195 215 247 320 000 029 033 041 019 062 031 18 - Zinc in Tartaric Acid H/100 Days C D 1 cc . Og *2 cc . 0. 0 - 0.1 0.000 0.000 0.000 0.000 1 0.1 1.13 0.049 0.30 0.096 2 0.22 2.35 0.108 1.46 0.052 3 0.10 2.48 0.127 1.60 0.071 4 - 0.46 2.45 0.180 1.50 0.012 5 - 0.10 3.51 0.208 2.23 0.126 6 - 0.24 3.05 0.195 2.30 0.144 7 0.66 4.38 0.187 3.70 0.137 9 0.25 4.38 0.226 3.79 0.181 1 cc^>16.8 N/ 1000 1 000=17 .6 0 - 0.89 0.55 0.000 0.53 0.000 1 - 0.83 1.30 0.028 1.35 C.038 2 0.80 3.15 -0.014 3.56 0.002 3 1.05 3.60 -0.004 5.38 0.076 4 0.24 3.27 0.0399 5.55 0.164 9 1.29 10.80 0.374 13.80 0.506 10 0.75 11.12 0.446 13.20 0.525 1CC017.6 1 ccO-18 .4 Tin in Tartaric Acid E/1000 19- Days C ®i CC . Og B 2 cc . 0 2 0 — 0.89 0.4 0.000 0.53 0.000 i 1 -0.83 0.6 0.00704 0.9 0.0187 2 0.80 2.32 0.0416 2.55 - 0.0277 3 1.05 2.7 0.0409 2.9 - 0.0277 4 0.24 1.68 0.0229 1.83 - 0.0218 9 1.29 2.91 0 . 0421 3.22 - 0.0276 10 0.75 2.3 1 cc=C=15 B/100 0.0315 1 2.32 cc=o=15 - 0.0219 0 -0.1 - 0.15 0.0000 •0.17 0.0000 1 0.1 0.2 0.C0021 0.3 0.0052 2 0.22 5.57 0.0287 0.33 - 0.0043 3 0.1 7.05 0.0381 0.17 0.00302 4 - 0.46 7.72 0.445 - 0.2 0.02186 6 - 0.1 9.15 0.517 — 0.13 0.0221 7 - 0.24 9.3 0.537 — 0.2- 0.0114 8 0.66 10.75 0.505 1.0 0.0064 10 0.25 10.93 i cc=c=ie H/10 0.581 1 0.59 CC =0:18 0.0063 0 - 0.89 0.52 0.0000 0.45 o.ooco 1 - 0.83 2.49 0.108 2.29 0.132 2 0.80 4.48 0.038 4.28 0.127 3 1.05 5.88 0.112 5.57 0.191 4 0.24 5.32 0.159 5.21 0.251 9 1.29 9.75 0.305 9.92 0.510 10 0.75 9.25 1 ccoig ■K 0.328 1 9.40 cc=C>13 . 2 0.519 0 - 0.1 - 0.4 0.000 — 0.3 0.000 1 0.1 1.19 0.0549 1.16 0.0596 2 0.22 2.32 0.190 3.48 0.209 3 0.1 3.9 0.244 4.23 0.273 4 — 0.46 3.93 0.305 4.47 0.352 6 - 0.1 4.59 0.310 5.23 0.362 7 - 0.24 4.26 0.310 5.12 0.367 8 0.66 4.97 0.266 6.24 0.358 10 0.23 4.83 1 c c =C»1 5 0.293 1 5.7 cc =015 0 .363 Copper in Tartaric Acid H Days C D 1 cc . 0 2 ^2 CC . Or 0 - 0.10 - 0.50 0.000 - 0.35 0.000 1 0.10 0.00 - 0.0186 0.35 0.019 2 0.22 0.28 0.028 0.50 0.016 3 0.10 - 0.22 0.002 0.16 0.009 4 - 0.46 - 1.02 - 0.003 - 0.92 0.009 5 - 0.10 - 1.50 - 0.076 - 1.27 - 0.048 6 _ 0.24 - 2.03 - 0.102 - 1.85 - 0.070 7 0.66 - 0.95 - 0.107 0.07 - 0.049 9 0.25 - 1.75 - 0.128 - 0.05 - 0.017 10 - 0.89 - 3.71 - 0.167 - 4.44 - 0.150 11 - 0.83 - 3.32 - 0.144 0.00 - 0.089 12 0.80 - 1.65 - 0.173 0.00 _ 0.070 13 1.05 - 1.35 - 0.174 - 0.24 - 0.007 15 0.24 - 2.45 - 0.180 - 0.90 — 0.063 20 1.29 - 1.32 - 0.195 - 2.08 - 0.230 21 0.75 - 2.32 - 0.220 - 1.52 _ 0.147 1 cc = C =-13 .2 1 oc =018 li /100 0 - 0.10 ” 0.26 o.oco - 0.23 0.000 1 0.10 0.84 0.041 0.90 0.070 2 0.22 2.61 0.126 2.41 0.148 3 0.10 3.17 0.167 2.94 0.199 4 - 0.46 2.6 0.190 2.98 0.256 5 - 0.10 4.77 0.274 3.59 0.267 6 - 0.24 4.54 0.274 3.39 0.275 7 0.66 5.59 0.242 5.80 0.356 9 0.25 5.47 0.278 5.70 0.414 10 - 0.89 5.504 0.386 4.70 0.424 11 - 0.83 4.70 0.349 4.94 0.447 12 0.80 6.38 0.274 6.57 0.398 13 1.05 6.68 0.268 7.16 0.408 15 0.24 6.03 0.308 6.20 0.474 20 1.29 5.47 0.176 7.65 0.432 21 0.75 6.88 0.306 6.98 0.434 1 cc ^> 18.4 1 cc ^ C = 13.6 Pl ft T E Dh rs * . S'A h/CJ D n y_5 25 - sorae work on the corrosion of tin in tartaric acid. He analyzed the corrosion product and found that it consisted of a mixture of oxides of tin. This would be expected from the fact that tin compounds as a rule hydrolyze easily. Aluminum corrodes appreciably in normal and .01 K tartaric acid and does not corrode at all in 0.1 and .001 IT. Something analogous to this has been described by Heyn and Bauer^ who worked with iron and steel in various salt solutions. They found that in many cases (all that they recorded) the corrosive action does not vary with the concentration of solution in any regular manner. The data on aluminum also contradicts somewhat the statement of G. H. Bailey that the corrosion of aluminum in tartaric acid is negligible. Zinc corrodes more rapidly in .001 II tartaric than in .01 H. As in the case of propionic acid, zinc in normal and 0.1 F solutions reacts to give hydrogen. (d) Citric acid ( Tables IX, X, XI, XII; Plates IX, X, XI, XII).- xhe results obtained w r ith citric acid are closely analogous to those obtained with propionic except in the case of aluminum. Aluminum in the more dilute acids corrodes more rapidly than in the more concentrated. (e) Alanine (Tables XIII, XIV, XV, XVI; Plates XIII, XIV, XV, aVI) .- Prom the fact that alanine contains both an amino group and a carboxyl group, we would not expect it to behave like an ordinary acid. Guch an assumption is fully justified by the re- sults obtained , especially with copper and zinc. Copper is corroded very rapidly in alanine, and a very dark blue solution results. This leads to the conclusion that copper t . Copper in Citric Acid E Days C *2 cc . Og D 2 cc . 0 0 0.50 0.05 0.000 - 0.05 0.000 1 0.46 0.70 0.040 0.84 0.063 £ 0.33 1.06 0.072 1.35 0.115 3 -0.15 1.10 0.121 1.46 0.169 4 0.14 1.18 0.097 1.48 0.143 5 0.12 0.95 0.087 1.24 0.127 7 - 0.12 0.95 0.109 1.25 0.149 9 0.05 0.98 1 cc*>18 0.096 1.13 1 cc:C&3.2 0.125 E/ 10 0 1.09 0.26 0.000 0.25 0.000 1 0.40 0.33 0.070 0.22 0.059 2 “ 0.12 0.10 0.107 0.00 0.092 4 -0.C7 0.20 0.108 - 0.10 0.080 8 0.00 0.68 0.0532 - C.24 0.062 10 - 0.52 0.78 0.096 -0.24 - C .050 13 - 0.59 0.25 1 00=018 0.133 - 3.08 1 ccoG.3.2 - 0.096 E/100 0 0.50 0.29 0.000 0.24 0.000 1 0.46 0.54 0.017 0.52 0.019 2 0.33 0.55 0.032 0.63 0.032 3 -0.15 0.92 0.096 1.10 0.109 4 0.14 1.00 0.073 1.20 0.087 5 0.12 1.02 0.076 1.21 0.089 7 - 0.12 1.02 0.099 1.22 0.113 9 0.05 1.09 0.091 1.43 0.108 1 ccol8.4 1 ccol8.4 E/lOOO 0 1.09 0.20 0.000 0.27 0.000 1 0.40 -0.41 0.078 -0.27 0.025 2 -0.12 -0.99 0.050 -0.72 0.041 4 -0.07 -0.79 0.096 -0.56 0.049 8 0.00 0.66 0.129 -0.52 ' 0.045 10 -0.52 -1.27 0.073 -1.09 0.052 13 -0.59 -1.28 0.079 -1.09 0.056 1 CC=Crl 8 1 cc =o=15 27 - Aluminum in Citric Acid B Lays C D 1 cc. Og »2 0 0.50 -0.15 0.000 -0.23 1 0.46 . 0.2 0.025 - 0.50 2 0.33 0.05 0.027 0.44 3 -0.15 -0.1 0.065 - 0.51 4 0.14 -0.09 0.038 - 0.40 5 0.12 -0.1 0.039 0.40 7 -0.12 0.09 0.073 - 0.28 9 0.05 0.41 0.076 0.23 1 ccsO.6. 8 1 ccol7 E/10 0 1.09 0.15 0.000 0.19 1 0.4 C .45 0.084 -0.44 2 -0.12 -0.77 0.062 — C .72 4 -0.07 -0.25 0.104 -0.07 8 0.00 0.39 0.119 0.46 10 -0.52 0.07 0.142 0.16 13 -0.59 0.38 0.130 0.49 1 cc«Q.6. 8 1 c co-1 7 H/100 0 0.50 0.45 0.000 0.16 1 0.46 0.48 0.005 0.30 2 0.33 0.70 0.035 0.49 3 -0.15 0.88 0.086 0.56 4 0.14 1.13 0.071 0.82 5 0.12 1.25 0.080 0.86 7 -0.12 1.45 0.115 1.13 9 0.05 1.90 0.124 1.60 1 CC018 1 ccol8 E/1000 0 1.09 0.10 0.000 0.15 1 0.40 — 0.20 0.0717 0.29 2 -0.12 —0.68 0.075 -0.73 4 -0.07 -0.35 0.087 - 0.45 8 0.00 — 0.13 0.092 - 0.21 10 — 0.52 - 0.74 0.109 -0.73 13 -0.59 — 0.75 0.115 -0.67 1 cc-=c=18 .4 1 CC=C=l8 cc . Og 0.000 — 0.073 0.053 0.046 0.051 0.050 0.033 0.086 0.000 0.080 0.065 0.097 0.120 0.153 0.177 0 . 000 0.0116 0.035 0.085 0.071 0.075 0.113 0.123 0.000 0.076 0.071 0.081 0.087 0.109 0.119 28 - Tin in Citric Acid T.T Days C D 1 Li cc . 0 2 D 2 0 0.50 0.33 0.000 0.05 1 0.46 1.88 0.1173 2.15 2 0.33 2.58 0.1827 3.45 3 -0.15 2.94 0.2545 4.41 4 0.14 3.33 0.2537 5.12 5 -0.12 5.42 0.2640 5.43 7 0.12 4.22 0.3453 5.95 9 0.05 5.00 u.3864 6.62 1 cc^13.6 1 cc^c=18 0 1.09 0.52 0.000 0.40 1 0.4 1.93 0.265 1.24 2 -0.12 2.15 0.234 2.39 4 -0.07 6.08 0.519 5.19 8 0.00 8.73 0.709 7.49 10 -0.52 8.75 0.759 7.58 13 -0.59 9.15 0.796 8.08 1 cc **13 . 6 1 cc=c=18 K/100 0 0.50 0.03 0.000 0.54 1 0.46 3.20 0.197 2.35 2 0.33 4.56 0.300 3.52 5 -0.15 5.3 0.395 4.15 4 0.14 5.58 0.386 4.81 5 0.12 6.05 0.420 5.07 7 -0.12 6.55 0.477 5.54 9 0.05 7.39 0.515 7.37 1 cc=c=15 1 cc ^18 H/ 1000 0 1.09 0.2 0.000 0.29 1 0.40 -0.2 0.0396 -0.35 2 -0.12 •0.33 0.0809 -0.94 4 — 0.07 0.52 0.133 -0.65 8 0.00 0.69 0.137 0.59 10 -0.52 0.06 0.145 -1.13 13 -0.59 0.16 0.149 — 1*09 1 00=0*15 1 cc-**15 cc . Og C.000 0.121 0.203 0.324 0.316 0.336 0.435 0.407 0.000 0.112 0.226 0.377 0.498 0.552 0.587 0.000 0 .1022 0.1761 0.2561 C .2660 0.2837 0.3318 0.4140 0.000 0.227 0.232 0.343 0.4729 0.57C * Zinc ii Days C % 0 0.5 0.00 1 0.46 -0.70 S 0.33 1.30 3 -0.15 0.47 4 -0.14 0.70 5 0.1E 0.80 7 -0.1S 1.17 9 0.05 1.91 1 cc=e=15 i Citric Acid E/100 cc. 0 2 D S cc . l 0.000 0.00 0.000 0.043 -0.E8 0.017 0.1C3 0.19 0.031 0.094 1.04 0.016 0.07E 0.90 0.10E 0.091 0.8E 0.098 0.114 -0.3 0.08S 0.171 0.77 0.10E 1 cc^LS.E 0 1 E 4 8 10 13 1.09 0.4 -0.1E -0.07 0.00 -0.5S — C .59 E/1000 0.3 0.000 0.08 0.054 -0.C7 0.096 0.14 0.097 0.54 0.118 -0.1S 0.133 -0.11 0.139 1 cc=£>18.4 0.41 0.000 • 0.09 0.048 -0.S9 0.077 0.10 0.081 C.55 0.113 — 0. S3 0.119 - 0.04 0.136 1 cc=O18.0 P l n ~r e TK. Dft YJ S' A t=/ Cl P L- /-? -r B XL f Dft ys D n ys Zinc in Alanine K/10 Days 0 D 1 cc . 0£ *2 CC . Or 0 0.7 1.21 0.000 2 0.4 4.95 0.218 4 -0.4 6.77 0.403 6 -0.4 9.15 0.525 8 0.6 11.80 0.573 10 1.17 16.15 0.744 1 cc^18 N/100 0 0.99 0.24 0.000 0.36 0.000 1 -0.2 2.95 0.318 3.3 0.279 2 0.1 4.52 C.409 5.29 0.358 4 0.7 7.00 0 • 635 8.69 0.491 6 0.82 9.45 0.714 9.66 0*534 7 0.82 11.56 0.878 10.15 0.506 9 0.78 11.54 0.876 11.22 0.242 1 00*0.3.2 o • CO 4 o o H IT/ 1000 0 0.& 2.6 0.000 1.02 C.000 2 0.4 6 .36 0.238 5.3 0.338 4 -0.4 7.97 0.403 7.17 0.447 6 -0.4 10.0 0.516 9.19 0.568 8 0.6 12.56 0.563 10.82 0.554 10 1.17 14.2 0.687 1 ccx:18 1 cc*18.0 Tin in Alanine 36 - E lays C D 1 cc . 0 2 »2 cc . 0 ( 0 0.99 0.05 0.000 *-0.4 0.000 1 -0.2 1.09 0.191 0.74 0.153 2 0.1 1.52 0.193 0.86 0.130 4 0.7 2.41 0.201 2.51 0.165 6 0.82 2.93 0.228 1.89 0.138 7 0.82 3.74 0.288 2.05 0.137 9 0.78 3.55 loc^>13 . 6 0.279 2.21 1 CC=Crl8 0.141 E/10 0 0.7 1.31 0.000 1.54 0.000 2 0.4 1.4 0.034 1.6 0.034 4 -0.4 0.48 0.060 0.78 0.048 6 -0.4 0.54 0.063 0.089 0.057 8 0.6 1.89 0.041 2.23 0.062 10 1.17 2.6 0.026 2.98 0.064 1 ccol8 1 cc**13.2 E/100 0 0.99 0.15 0.000 0.56 0.000 1 -0.2 0.2 0.117 1.55 0.181 2 0.1 1.47 0.159 1.90 0.175 4 0.7 2.18 0.140 2.56 0.161 6 0.82 2.36 0.139 2.72 0.160 7 0.82 2.37 0.159 2.80 0.165 9 0.78 3.21 0.190 2.75 0.165 1 cc=e=18 1 CCsOO.5.0 E/1000 0 0.7 2.7 0.000 1.99 0.000 2 0.4 3.08 0.053 2.11 0.036 4 -0.4 2.32 0.084 1.26 0.056 6 -0.4 2.40 0.089 1.38 C.066 8 0.6 3.22 0.037 2.69 0.057 10 1.17 4.41 0.049 3.31 0.042 1 ccoQ.8 . 4 1 c c.=c*15.0 Aluminum in Alanine Days 0 1 2 4 6 7 9 0 2 4 6 8 10 0 1 2 4 6 7 9 0 2 4 6 8 10 TS G *>1 oc. Cg »2 CG.Og 0.99 0.12 0.000 0.15 0.000 -0.2 1.07 0.171 0.83 0.0381 0.1 1 » 52 0.169 0.95 0.0544 0.7 1.46 0.170 1.35 0.0097 0.82 3.33 0. 209 1.70 0.0279 0.82 3.86 0.234 2.21 0.0570 0.78 4.04 0.255 1.89 0.0427 1 cc^iLG .8 1 cc*c0l7 . 6 H/lO 0.7 1.46 0.000 1.20 0.000 0.4 1.99 0.060 2.1 0.079 -0.4 2.19 0.149 2.83 0.198 -0.4 4.16 0.266 0.00 0.037 0.6 0.08 1.17 ( exploded ) ( exploded ) 1 cc*s£L6 .8 1 cc=&17.6 E/100 0.99 0.42 O.OCO 0.52 0.000 -0.2 1.39 0.168 2.28 0.215 0.1 1.82 0.164 2.85 0.212 0.7 2.76 0.155 4.91 0.266 0.82 3.26 0.170 6.48 0.342 0.82 3.40 0.177 7.19 0.379 0.78 3.74 0.201 7.99 0.425 1 ce^l8.4 1 cc*JiL8 .4 D/1000 0.7 0.71 0.000 0.4 0.86 0.037 -0.4 0.03 0.069 -0.4 0.04 0.069 0.6 1.36 0.045 1.17 2.12 0.032 1 ee*>18.4 2 .24 0.000 3.8 0.012 0.72 0.018 ( exploded) cc .4 1 Copper in Alanine N 35 - Lays 0 1 2 4 6 7 9 0 2 4 6 8 10 0 1 2 4 6 7 9 0 2 4 6 8 10 c D 1 GG . Og ®2 CG . Og 0.99 0.15 0.000 0.2 0.000 — 0.2 2.43 0.2415 -0.4 0.827 0.1 4.10 0.305 0.39 0.728 0.7 6.6 0.387 0.6 0.496 0.82 8.38 0.473 0.58 0.370 0.82 9.2 0.518 0.33 0.235 0.78 10.2 0.579 0.89 0.578 1 cc =£ t 18 . 0 1 oc4>18 .4 IT/10 0.7 1.31 0.000 1.58 0.000 0.4 4.54 0.266 5.33 0.314 -0.4 5.49 0.413 7.58 0.438 -0.4 6.38 0.477 9.49 0.544 0.6 9.26 0.595 11.49 0.569 1.17 10.96 0.664 14.18 0.654 1 cc ^» 13 . 6 1 C 0 = 018 . 0 1/100 0.99 2.28 0.000 0.35 0.000 -0.2 2.2 0.109 0.13 0.1 3.13 0.142 0.1 0.666 0.7 4.73 0.191 0.1 0.084 0.82 5.1 0.205 0.05 0.064 0.82 5.09 0.204 0.07 0.049 0.78 5.1 0.209 0.1 0.012 1 cc=ol5 1 cc*c=13.2 IT/ 1000 0.7 0.68 0.000 0.43 0.000 0.4 1.25 0.072 0.23 0.015 —0.4 0.68 0.106 — 0.43 0.0484 -0.4 0.68 0.106 -0.27 0.0591 0.6 1.95 0.106 1.07 0.0435 1.17 2.73 0.112 2.79 0.0392 1 cc=csl3. 2 1 g £ ^<>15 .0 . P L- Fl ~TE Z S' a y a D /=? YS [Zl a JJZ' D f=\ vs rA ^ cj 58- forms some sort of a complex with the amine, which is analogous to . + + the Cu(hH 3 ) 4 ion formed when BH 4 OH is added to a copper salt solution . Zinc also forms complex ions with NHg , and from its rapid corrosion rate in alanine, such a complex is probably formed in this case with the amine. (f) The Effect of Previous Treatment of the Metal.- The re- sults with aluminum in alanine were rather unexpected. Three pieces of aluminum, the three that gave such large amounts of hy- drogen.had been used several times before-, being carefully cleaned and polished between successive experiments. The other piece in .001 B acid was new. This brings out rather forcibly that previous treatment of a metal has much to do with speed of corrosion. In making the sheet of aluminum, the impurities present were probably covered up by a layer of pure aluminum. On continued treatment in acids this outer layer was dissolved off, exposing the impurities and giving opportunity for "selective" corrosion. All of these three pieces were pitted. xxiis problem is by no means finished. The author hopes to be able to clear up many points that have been touched on in this- paper, by later research, and to enlarge the scope of the work somewhat . . « , • - . . . - * 39 - SUMMABY I. Hate of corrosion is not a straight line function of the time, and cannot be accurately determined by measuring the amount of material removed after a given period of time, and assuming a uniform rate over the entire period. The reasons suggested are (a) the changing composition of the solution, and fb) the tendency for an inductive period at the beginning of the reaction. II. Two strips of metal, of the same size cut from the same sheet and treated in the same way do not corrode at the same rate because of surface differences which cannot be eliminated. III. There was no hydrogen evolved in most of the reactions studied . IV. The corrosion of pure metals in dilute organic acids is accompanied by t.ie absorption of oxygen and the amount of metal re moved is proportional to the amount of oxygen consumed. In ether words, it corresponds to the "complete” corrosion described by Bengough. /. The rate of corrosion of a metal in an unsubstituted acid is dependent upon the "solution tension" of the metal and the hydrogen ion concentration of the solution. VI. The effect of presence of OH groups as exemplified by tartaric acid cannot be explained in the light of the present theory and more v/ork is necessary to explain the results. >11. Ine presence of an amino group in the molecule leads to tne formation oi complexes analogous to complexes formed by copper ana zinc ions with EH 3 , and therefore these metals corrode more rapidly in this type of acid. /III. The rate of corrosion of a metal by acids ly on the previous treatment of the metal. depends large . . * . . • • , . * n> ■ , * . BIBLIOGRAPHY 1. Whitney ,-Joum. Am. Ghem. Soc. 25,-394. 2. Tilden,-Joum. Am. Ghem. Soc. 93,-1356. 3. Seligman and Williams ,-Jourg. Soo. Ghem. Ind . 36,-409. 4. Holleman ,-5th edition, page 241. 5. A. G. Chapman,- J. Chem. T. 775-103. 6. Heyn and Bauer , -"Tiber den Angriff des Eisens durch Wasser und WSsserige LSsungenV Mitteilungen aus dem Kdniglichen Materialprtifungsamt , Berlin,- 1910, 28,-62, 1908, 26,-2. 7. Bengough,-J. Inst. Met. 10,-50.