March 15, 1933
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INDUSTRIAL AND ENGINEERING
ratio of 9.3 x 10-5; the second sample had a chlorinity of 1.78 per mille, contained 0.41 mg. of fluorine, and gave a ratio of 22.0 x This would indicate that the diluting waters of the river had a fluoride-chlorinity ratio considerably greater than that of the sea. Further investigation with river water and the diluted sea water a t the mouths of rivers is contemplated, following a further study for detecting smaller amounts of fluoride by the method described above. From October, 1931, to July, 1932, samples were collected about once a week a t the surface from the observation platform a t the field laboratories of the Oceanographic Laboratories of the University of Washington, a t Friday Harbor, Wash. Thirty analyses showed an average chlorinity of 17.00 per mille with an extreme variation from 16.46 to 17.39 per mille; an average fluoride content of 1.24 mg. of fluorine per liter with a variation from 1.17 to 1.32 mg. of fluorine; and a fluoride-chlorinity ratio of 7.3 x Only one sample showed a variation greater than the calculated experimental error. DISCUSSION OF RESULTS Approximately 100 different samples have been analyzed for fluoride, and rtn average fluoride-chlorinity ratio of 7.0 X was obtained. Comparing the data given above for 30 samples of surface waters with Table 11,waters from the surface appear to have a slightly greater fluoride-chlorinity ratio. Of the samples discussed in Table 11, 41 were secured in the open ocean. The average ratio of these 41 samples (for all depths) was 6.85 X while that for “inside” waters (straits, sounds, bays, and inlets) was 7.18 X The maximum values for ocean waters were obtained in the surface samples and were never higher than 7.2 x while the maximum values of inside waters were 7.5 X The minimum ratio for the inside waters was obtained in the deep samples and more nearly approached the ratio for ocean waters. The average chlorinity for all the ocean waters was 18.23 per mille and that
CHEMISTRY
89
for the inside waters 17.16 per mille, or a difference of about 1 per mille. Assuming that an ocean water of 18 per mille chlorinity and average fluorine-chlorinity ratio is diluted by river water to 17 per mille, calculations show that the concentration of fluorine in the diluting water may vary from 0.15 to 1.2 mg., depending upon the value used for the experimental error. As the average river water has a chloride content of from 2 to 6 mg. of chlorine per liter, the fluoride-chlorinity ratio for fresh waters is many times greater and thus accounts for the very slight variations noted for inside waters and some surface ocean waters. CONCLUSIONS The zirconium nitrate-sodium alizarin sulfate method has been modified and is applicable for the analysis of sea water. The fluoride concentration of sea water is a function of the dissolved salts or chlorinity and ranges from 1.0 to 1.4 mg. of fluorine per liter. It shows no seasonal fluctuations, but increases with depth until approximately uniform conditions of salinity or chlorinity are encountered. The fluoride concentration is proportional to the chlorinity and the fluoride-chlorinity ratio is 7.0 X This ratio is slightly higher for surface coastal waters and for some waters of straits, channels, and estuaries. LITERATURE CITED Carles, P., Compt. rend., 144, 37, 437 (1907). Carnot, A., Ann. m i n e s , 10, 175 (1896). Casares, J., and Casares, R., Anales soc. espafi. fis. quim., 28, 1159-62 (1930). De Boer, J. H., 2. anorg. Chem., 152, 213-20 (1926). Forchhammer, G., “Proportion of Calcium Fluoride Present in the Baltic,” Edinburgh P h i l J . , 48, 345 (1850). Gautier, A., and Clausmann, P., Compt. rend., 154, 146975 (1912). Nat. Research Council, Bull. 85 (1932). Thompson, T. G., J . Am. Chem. Sac., 50, 681-5 (1928). RECEIVEDOctober 31, 1932
Removal of Corrosion Products from Iron THOMAS J. FINNEGAN AND RICHARD C. COREY,New York Steam Corporation, New York, N. Y.
C
ORROSION tests are usually made by subjecting the test specimens to the corrosive medium under the desired conditions and after a period of time removing the adherent corrosion products and determining the loss in weight of the specimens. In order to test different means of removing the corrosion deposits, several pieces of Bessemer wire were corroded and the corrosion products removed by four methods. The efficiency of each method in stripping the deposit from the metal was observed, and also whether or not the iron itself was attacked. Pieces of iron wire 4 to 5 cm. in length were pickled in sulfuric acid and inhibitor in order to remove any oxide coating, and then washed, dried, measured, and weighed. They were placed in a large desiccator over dilute hydrochloric acid and allowed to remain there for 144 hours. The cover of the desiccator was arranged to allow free circulation of air and the wires were well out of contact with the dilute acid. This atmosphere was highly corrosive and a t the end of the time period the specimend were covered with a deposit which consisted of red rust and black oxide of iron. They were then cleaned according to several methods and the losses in weight were found. As all the samples which
were cleaned by any one method had been in the corrosive atmosphere for the same length of time, it was assumed that about the same amount of corrosion would be experienced by each specimen, and that they would be checks on each other. The following methods were used to remove the corrosion products: 1. Brushing with a wire bristle brush. 2. Pickling with sulfuric acid containing an inhibitor. 3. Pickling with ammoniacal ammonium citrate. 4. Pickling with sodium hydroxide and zinc. The first three methods have been in use for many years. The fourth was recently described by Cournot and Chaussain (1). REMOVAL OF CORROSION PRODUCTS
A number of wires were removed from the container a t the same time and brushed by hand with a wire brush, alternating the brushings with washing under a stream of water. It was soon evident that only the loose surface oxide was being removed, and consequently the operation was continued using a motor-driven circular brush. After repeated
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The clean wires were then treated for 15 minutes more by brushings the specimens still had coatings of black oxide which it was impossible to remove. The samples were the same method which had been used to remove the corroweighed, however, in order to observe the agreement among sion products, in order to learn the effect of the different procedures on the metal itself. The results are reported several specimens. Other wires were removed from the corrosion atmosphere in Table I. Indications were that the sodium hydroxide and immersed in 15 per cent sulfuric acid containing 5 per and zinc treatment gave the best results, &sno attack of the cent of the inhibitor known as Barretts No. 20 pickling metal was found. It would appear that all three methods compound. The specimens soon became clean, and after are about equally efficient in removing the deposit, but that being well washed with distilled water followed by alcohol acid and inhibitor and the ammonium citrate are liable to and ether, they were dried with a soft cloth, allowed to stand cause high results because of some attack of the clean metal. If the specimens are watched carefully as in these tests, in a desiccator for about an hour, and then weighed. Other specimens were cleaned by heating them under a however, the slight attack is not large enough to change reflux condenser in a solution prepared by dissolving about materially the practical nature of the calculated results. All traces of deposit appeared to have been removed by 40 grams of citric acid in 100 cc. of ammonium hydroxide and adding excess ammonia. This treatment also left the metal the treatments, but the possibility existed that the apparent attack of the metal might have been caused by the removal bare in a short time. Cournot and Chaussain (1) recommend treating the speci- of some unnoticed scale left behind after the first pickling. mens with hot 20 per cent sodium hydroxide solution to I n order to check this, some pieces of clean iron wire of the which powdered zinc has been added. According to them, same stock and dimensions as the corrosion specimens were the violent evolution of hydrogen transforms the corroded subjected to the different procedures. The wires were first layer into granules which fall to the bottom of the beaker. pickled in sulfuric acid and inhibitor in order to remove any slight corrosion film that might have been on the surface. Several specimens were treated by this method. The losses in weight of the specimens when the corrosion They were then washed with distilled water and finally products have been removed by these different methods immersed in alcohol and ether. After being wiped dry with are given in Table I. Brushing is apparently worthless for a soft cloth, they were immediately placed in a desiccator these small specimens, the low weight losses indicating in- and rapidly weighed. Five specimens were placed in each complete removal of the deposit, and the lack of agreement of the three cleaning solutions and left there for an hour. showing that not even qualitative results can be obtained. At the end of this period they were washed with water, alcoThe samples cleaned by the other three methods showed hol, and ether, dried, and weighed. They were then replaced fair agreement, not only among the samples cleaned by any in the solutions for additional time and the total loss in one method, but also among the three different methods. weight found. Table I1 gives the average total loss in The specimens cleaned by ammonium citrate were corroded weight a t the end of the indicated time periods of the five in a different container from that used for the rest of the specimens treated by each method. samples in order to see if the corroding process itself were TABLE 11. EFFECT OF PROCEDURES ON CLEAN METAL reproducible. The results obtained were a little lower than Loss IN W E I Q A T AT ENDOF: those of the other three methods but are of the same order PROCEDURE 60 min. 90 min. 180 min. of magnitude and, from a practical standpoint, in fair agreeGram Gram Gram Sulfuric acid and inhibitor 0. 0012a 0 0013 ment. 0.0005 0. Ammonium citrate TABLE I. Loss OF WEIGHTOF SPECIMENS AFTER CORROSION Loss AFTER DIFFERENCE 15 MIN. FROM FIRST PROCEDTJRB Loss O N FIRST CLEANING ADDITIONAL Loss Gram % ’ Mg./sq,cm. Mg./sq.cm. Mg./sq.cn.
Sulfuric acid inhibitor Sulfuric acid inhibitor Sulfuric acid inhibitor Sulfuric acid inhibitor Sulfuric acid inhibitor Ammonium Ammonium ilmmonium Ammonium Ammonium
5.59 15.25 3.17 8.27 0.20 0.52 0.48 1.29 0.32 0.84
.....
0.0481
11.52 31.07
31.46
0.39
0.0560
12.98 36.18
36.43
0.25
0.0494
11.86
31.91
32.49
0.58
0.0354
8.68
22.87
22.87
none
0.0366
8 . 9 1 23.64
23.84
0.20
0,0343 0,0290 0.0303 0.0291 0.0338
8.73 7.16 8.03 7.20 8.79
22.08 18.73 19.57 18.91 21.83
22.48 18.73 19.64 19.19 21.83
0.40 none 0.07 0.28 none
0.0236a 0.0128 0.0008 0.0020 0.0013
Brushing Brushing Brushing Brushing Brushing and and and and and
citrate citrate citrate citrate citrate
..... ..... ..... .....
....
....
.... ,...
....
Sodium hydroxide and zinc 0.0393 9.37 25.39 25.39 none Sodium hydroxide and zinc 0.0492 11.70 31.78 31.78 none Sodium hydroxide and zinc 0.0467 11.18 30.17 30.17 none Sodium hydroxide and rino 0.0446 11.30 -28.75 28.75 none Sodium hydroxide and zinc 0.0494 12.05 31.91 31.91 none Each specimen weighed approximately 0.40 gram, and had a n area of approximately 1.50 sq. om. Individual weights and areas were determined exactly.
Sodium hydroxide and zinc 0.00006 a Each item is average of five specimens.
0 00006
0.00008
The sulfuric acid and inhibitor appear to attack the metal the most and the sodium hydroxide and zinc the least. The cause of the very low average for this last method is the fact that three specimens showed no weight loss a t all. The sulfuric acid and inhibitor procedure is the easiest to use and would be advantageous if the attack of the metal did not affect the magnitude of the results. It is a little troublesome to use ammonium citrate, as it loses its effectiveness if the ammonia is driven off, necessitating the use of a reflux condenser.
SUMMARY The corrosion deposits can be removed from iron wire specimens by means of sulfuric acid and inhibitor, ammonium citrate, and sodium hydroxide and zinc, all three methods giving efficient removal of the deposit. The use of sodium hydroxide and zinc according to the procedure of Chaussain and Cournot is preferable, as it does not attack the bare iron. Brushing as a means of removing deposit from small samples is worthless. LITERATURE CITED (1) Cournot and Chauasain, Compt. rend., 194, 1823 (1932). RECEIVED November 3, 1932.
