April, 1927
INDUSTRIAL A X D ElVGINEERING CHEMISTRY
46 1
Some Fumigation Tests with Chloropicrin’ By L. F. Hoyt and E. P. Ellenberger LARKINCo., INC.,BUFFALO,N. Y.
Experimental and small-scale commercial tests on the efectiveness of chloropicrin as a fumigant against certain insects. EJect of the fumigant on the germinating power of sezeral kinds of seeds and on a number of food products.
c
Strand38 recently reported good results in fumigating machinery in flour mills with a dosage of 5 pounds chloropicrin (diluted with an equal volume of carbon tetrachloride to promote rapid vaporization) per 1000 cubic feet. Strand found the Xediterranean flour moth to be easily killed but states that the confused flour beetle withstood dosages of 4 pounds chloropicrin per 1000 cubic feet. This author states that 1 pound of chloropicrin is equivalent to 10 pounds of carbon bisulfide or 80 pounds of carbon tetrachloride for fumigation purposes. Effect on Foods and on Germination of Seeds Moore3 reports that the germination of grain is not affected by exposure to a dosage of 0.3 pound per 1000 cubic feet; larger doses are claimed to be injurious unless the grain is thoroughly aired. Flour treated with chloropicrin retains sufficient gas to inhibit the growth of yeast slightly, and hence The high toxicity of chloropicrin t o various living organ- the baking qualities are somewhat affected although the bread isms, including insects, bacteria, fungi, and rodents, has been is not toxic. -\liegez3reports that the seeds of wheat, rice, hemp, and beet pointed out by several authors.? Neifert and Garrisonz1 state that it has undoubt,ed efficiency as an insecticide and suffered a loss of 30 to 40 per cent of their germinating power that in general it is more poisonous to stored-product insects by a 24-hour exposure to a concentration equivalent to 1.6 than hydrocyanic acid. The fact that chloropicrin rapidly pounds per 1000 cubic feet although the seeds of flax and sevpenetrates animal tissues to an unusual depth, apparently eral legumes lost none of their germinating power when exby reason of some peculiar ability to pass through the chitin- posed to a concentration of over 5 pounds per 1000 cubic feet. state that corn fumigated with 2 pounds ous covering of insects, as demonstrabed by Moore,z is no Piutti and per 1000 cubic feet for 8 days loses one-third of its germinating doubt the cause of its efficacy. power. Dosage for Commercial Fumigation The data of AIiege on wheat are contradicted by the evidence of pied all^,^^ who found that exposure to a concentraPiutti and Mango” recommend the use of chloropicrin a t the rate of 2 pounds per 1000 cubic feet for the fumigation of tion of 0.6 to 2 pounds per 1000 cubic feet did not reduce the cereals, and state further that it should be allowed to act for germinating power. Chapman and have made extensive tests with 8 days where large amounts of grain are being fumigated. Wille25recommends 4 pounds per 1000 cubic feet for 24 hours chloropicrin and studied particularly its effect on flour, as in fumigating large stacks of grain. YamamotoZ*mentions being of importance in the fumigation of flour mills. These the destruction of insects in wheat and rice by spraying authors found chloropicrin to be highly toxic to insects and chloropicrin into a warehouse at the rate of 0.4 to 0.6 pound noted particularly that. in contrast to most fumigants, chloroper 1000 cubic feet for a contact period of 48 to 70 hours. picrin continued to be toxic to insects at temperatures as low pied all^^^ states that 0.6 t’o 2 pounds chloropicrin per 1000 as 0” C. The presence of chloropicrin in flour affects fermentation adversely and results in a poor loaf made from such cubic feet are usually sufficient. flour, but fumigated flours given proper exposure to the air 1 Received February 18. 1926. showed complete recovery from the chloropicrin treatment. * Chloropicrin appears t o have been first prepared by Stenhouse [.inn., An exhaustive bibliography of 287 references on chloro66, 241 (1848)l b y the interaction of picric acid and chloride of lime. It picrin has recently been compiled by Roark, 39 which contains is described by him as a heavy, colorless oil, which attacks the eyes severely. Kekule [ A n n . , 101, 212 (1857); 106, 144 (lS5S)l prepared it b y several remany data on its manufacture and uses both in warfare (1) interaction of sodium chloride, concentrated nitric acid, actions-viz., and as an insecticide or fumigant.
HLOROPICRIS (or nitrochloroform), CNOzC13,is a colorless liquid of specific gravity 1.654 a t 20”/20” C., boiling a t 112” C.* It was produced in large quantities during the Korld F a r and was valuable in chemical warfare because it acted both as an asphyxiating lethal poison and as a lachrymator. According to Fries and West’s “Chemical Yarfare,” a concentration of 0.019 mg. chloropicrin per liter of air will cause a copious involuntary flow of tears. This concentration is only about 1/630 of that developed in practical fumigation with chloropicrin when doses of 0.8 pound per 1000 cubic feet are used and explains one of the great advantages of chloropicrin in commercial fumigation -viz., the self-protective feature or warning given by concentrations of the gas much smaller than could possibly be lethal. Toxicity of Chloropicrin
a n d ethyl alcohol; (2) chloral and concentrated nitric acid; and (3) methanol a n d sulfuric acid distilled with potassium nitrate, and sodium chloride. Hoffman [.4nn., 139, 1 1 1 (186611 described in detail the preparation of chloropicrin in 5-kg. quantities b y the action of chloride of lime on a saturated aqueous solution of picric acid, a yield of 114 per cent based on t h e picric acid being obtained b y distillation of t h e mixture. For description of various commercial methods by which chloropicrin may be prepared see Schotz, “Synthetic Organic Compounds,” p . 295, Ernest Benn, Ltd., London, 1925. Chloropicrin is now obtainable in commercial quantities under the name of “Larvacide” from Innis, Speiden & Co., Inc., 46 Cliff St.. h-ew York City, for whom i t is manufactured b y t h e 1x0 Chemical Co., Inc., of Niagara Falls, N. Y. See bibliography a t end of article. Numbers in text refer to this bibliography.
t
Experiments in One-Gallon Container Corn meal, heavily infested with confused flour beetle (Tribolium conjusz~m)in a small cloth sack, was placed in a 1-gallon container into which mas introduced 0.03 cc. (50 mg.) of chloropicrin through a small opening, which was then quickly sealed. After a contact period of 48 hours a t 21” C. all the insects, adults and larvae, were found to have been killed by this concentration, equivalent to 0.8 pound per 1000 cubic feet. A test made on a few specimens of the larvae of Dermestes wulpinus confined about 4 inches below the surface of dried
462
INDUSTRIAL AND ENGINEERIXG CHEMISTRY
tankage which nearly filled a gallon container indicated that a concentration of chloropicrin equivalent to 1.25 pounds per 1000 cubic feet was necessary to kill the insects in 48 hours. E x p e r i m e n t s in G a s - T i g h t C o m p a r t m e n t (22.7 C u b i c Feet)
A gas-tight compartment was constructed from a packing case lined with corrugated box board to which was applied a liberal coating of silicate of soda. The following materials were subjected to fumigation: oats, corn, wheat, and buckwheat in 5-pound cloth bags, raw Virginia peanuts (shelled), cocoa, rolled oats, macaroni, and polished rice in 5-pound paper bags; pastry flour, wheat cereal, and cornstarch in 1pound paper cartons, the last three materials being heavily infested with the confused flour beetle (Tribolium confusum Duv.) present both as adults and larvae; Indian meal moth (Plodia ilzterpunctella Hbn.) , including moths, larvae, and pupae, confined in a wide-mouthed flask the opening of which was covered with gauze. Six wide-mouthed flasks of about 60 cc. capacity mere nearly filled with wheat cereal heavily infested with the confused flour beetle. The mouth of each flask was covered with a piece of cotton gauze, tied about the neck of the flask. One of these flasks was completely buried in the contents of each of the bags of unhulled oats, rolled oats, polished rice, and cocoa; one flask was placed on the bottom of the box; and the remaining flask was suspended near the top of the box with its mouth within one-half inch of the box cover. I n this case, to effect a destruction of the insects, the gas would have to find its way into the flask and its contents by a very narrow opening. All these materials were placed in the box and the cover was sealed on. A quantity of chloropicrin amounting to 5 cc. (8.25 grams), equivalent to a dosage of 0.8 pound per 1000 cubic feet, was introduced into the box through a small opening in the cover and the opening then tightly closed. The box was allowed to remain sealed for 48 hours, the prevailing temperature being 21" C., then opened and aired for 3 or 4 hours. Within less than 24 hours after fumigation the rolled oats and macaroni were cooked in the usual manner, the peanuts were roasted, and a beverage was prepared from the cocoa. No abnormal odor or flavor could be detected in these foods. either uncooked or cooked, and when cooked these four foods were all palatable. EfTect on Insects. (1) Confused flour beetles and larvae in glass flasks. The infestation of the wheat cereal used was such t h a t 60 cc. of the product contained on the average 65 adult beetles and 46 larvae of various ages. I n four of the flasks undergoing fumigation all the insects were dead after 48 hours. I n the case of the flasks buried in cocoa and rolled oats a few insects (15 beetles and 4 larvae) were alive a t the end of the 48-hour contact period but died within 3 days afterward. Control experiments have shown t h a t this beetle will live for weeks, and even months, in wheat cereal and other cereal products in glass flasks or tin cans, with a very low mortality, only a few of the adult beetles dying. (2) All flour beetles and larvae in cereal products in cartons were killed even though some of the cartons were tightly sealed, showing t h a t the gas penetrates well through paper and cardboard. (3) Indian meal moths in all stages were killed. The pupae were kept under observation for 1 month and none developed into moths. F u m i g a t i o n of Warehouse R o o m (75,000 C u b i c Feet)
The room that was fumigated is on the top floor of a group of adjoining factory buildings and has brick walls and concrete floor. The room receives light from two large skylights which project above the roof from 8 to 10 feet. Its dimensions are 126 x 38 x 14 feet (not including skylights). EXPERIMENT I-The material fumigated consisted of twelve carloads of sunflower seed, packed in miscellaneous
Vol. 19, No. 4
burlap bags and stacked usually ten high. The seed was infested in varying degrees with the Indian meal moth present in the form of adult moths, pupae, and numerous larvae. The chloropicrin was introduced by forcing it by means of compressed air through a system of piping equipped with spray nozzles. A l/r-inch galvanized iron pipe was suspended about 1 foot from the,ceiling. This pipe was provided with six nozzles a t intervals of about 15 to 18 feet. The l/d-inch pipe was run out to the roof through the skylight and equipped with suitable valves and unions for attachment to the cylinder of gas. Before the fumigation each of the six nozzles was tested individually by connecting the line to a 100-pound air-pressure line. All openings t o the room were thoroughly sealed. The cylinder of chloropicrin, containing 60 pounds of the liquid, was transported to the roof and connections were made between the 100-pound air line, the sprayer line, and the cylinder by means of a special piping assembly. The air pressure was turned on and the liquid forced through the system. Some of the nozzles could be observed through the skylight and the chloropicrin could be seen issuing in the form of a fine mist. The room was left sealed for one week, opened, and aired for several hours before entering. (This contact period of one week was of course a favorable factor, and was longer than is ordinarily possible in commercial fumigation.) It was then found to be possible to stay in the room for several minutes without great discomfort. Food products, including flour, cocoa, rolled oats, and macaroni in paper bags, and lard and butter in 1-pound cartons, which were placed in the room before fumigation and were subjected to the action of the fumes of chloropicrin for a week, were examined and used as food within 24 hours after being removed from the room. None of the foods tested showed any off odor. taste. or damage. and were palatable and wholesome.
Five-pound cloth bags of buckwheat, corn, oats, wheat, and sunflower seed were also subjected to this same fumigation and germination tests were made on the seed thus fumigated and on controls not fumigated. Table I shows the dosage of chloropicrin required for spaces of different capacity and Table I1 the results of the germination test on seed fumigated for l week in the warehouse room. Table I-Dosage of Chloropicrin for F u m i g a t i o n (Basis, 0.80 Ib. per 1000 cu. ft.) Lbs. Cc. Storage room capacity 75,000 cu. ft. 60 Average box har capacity 2500 cu. ft. 2 550 Small room, 10 j , 12 x S L /ft. ~ 0.8 200 1.0 Small box, 5 cu. ft. 1-gallon container 0.03 T e s t s on Seeds F u m i g a t e d for 1 Week w i t h Chloropicrin (Rate, 0 8 Ib. per 1000 cu. ft.)
Table 11-Germination
SEED
FUMIGATED puMroATEn (CONTROL)
NOT
Per cent
Per cent
This fumigation took place in the latter part of September, 1925, and the prevailing temperature during fumigation was 20" to 25' C. The room was carefully inspected after the fumigation was completed and no live insects either moths, pupae, or larvae of the Indian meal moth were found. Some of the seed was left in storage in this room for 8 months. During much of this time-i. e., during the winter and early spring-the temperature in the room was not over 10" C., though always maintained above 0" C. Fumigation appeared to have been a 100 per cent success until April-May,
April, 1927
INDUSTRIAL A N D ENGINEERING CHEMISTRY
1926, when considerable numbers of adult Indian meal moths began to emerge from the small amount of seed then remaining in storage. Fresh infestation of the seed from outside the room was impossible under the prevailing conditions and furthermore there was no evidence of the larval stage of the insect. Hence it seems probable that reappearance of the adult moth was due to the fact that a number of the pupae of this insect survived the fumigation, remained dormant in the cold weather which followed the fumigation, and emerged with the onset of warmer weather in the spring. EXPERIMEXT 11-Material fumigated consisted of fifteen carloads of cottonseed meal in 100-pound bags, infested in varying degrees with confused flour beetle (Tm’bolium confusum) and to a lesser extent with the Mediterranean flour moth. Additional food products, including raisins, prunes, nut margarine, nut meats, and nuts in the shell, were placed in the room during fumigation and were freely exposed to the fumes of chloropicrin. The dosage used was 100 pounds of chloropicrin, equivalent to 1.33 pounds per 1000 cubic feet. The chloropicrin was contained in two 50-pound cylinders, each of which was equipped with a piping assembly with one nozzle and connected by flexible pressure tubing to a small cylinder of compressed air under 500 pounds pressure; this system of releasing chloropicrin having been developed by the Isco Chemical Company, who manufacture this fumigant. The “gas” is released in the form of a fine mist by simply turning on the supply of high pressure air. This fumigation took place in July, 1926, and the room was kept closed for 6 days, when it waJ entered, by operators wearing gas masks, for inspection. There was no evidence of any live moths, but a small percentage of the very large numbers of confused flour beetles that were found on the floor near the cylinders were alive and crawling about in a normal manner. The proportion of live beetles was less than 3 per cent of the total number. It should be noted that the effect of chloropicrio is to drive these beetles out of the infested material and it has been repeatedly observed that they seem to congregate in the largest number close to the cylinders from which the gas is released and where it presumably has a higher concentration, a t least in the early part of the fumigation. As a control experiment a small quantity of pancake flour, heavily infested with larvae and adult of the confused flour beetle had been placed in a £ flour bag securely tied. This bag was wedged between sacks of cottonseed meal in the warehouse room and subjected to fumigation. When the room was opened on the seventh day after fumigation started, this pancake flour was carefully examined. Of the 590 adult beetles and 366 larvae present in the ‘/4 pound of pancake flour, only 4 larvae were alive and these died within 3 days. No re-infestation of this pancake flour occurred during the subsequent 3 months that the sample was under observation, indicating that eggs of this insect had also been killed. The food products which had been placed in the room were removed and tasted LI~S soon as the room could be entered without a gas mask. All were found to have entirely normal flavors, showing that there was no absorption of chloropicrin perceptible to taste by such products as fats (either water-free such as lard, or containing water as nut margarine). nut meats, nuts in the shell, or dried fruits. EXPERIMENT 111-Fumigation was repeated in August, 1926, with the same dosage and method of application as in Expt. I1 on a new lot of cottonseed meal similarly infested. Conditions were such that the room could be left closed for 2 weeks. When opened it was found that the concentration of the gas was then so low that one could enter the room without a mask and remain a few minutes, although the residual gas was sufficient to induce coughing. Examination showed
463
the same large numbers of confused flour beetles congregated on the floor near the cylinders. Over a considerable area the numbers ranged from 100 to 300 beetles per square foot and only 2 to 3 per cent of these beetles were alive. After the room had been ventilated, 100 live confused flour beetles were carefully collected and placed in cottonseed meal in an open container. After 5 days only 5 of the 100 were alive. The results of this fumigation indicate that a very long contact period, such as 2 weeks, with an initial concentration of 1.33 pounds per 1000 cubic feet, has no advantage over a shorter period. The actual concentration of the gas developed a t various stages of fumigation is not known and may of course have been considerably less than the potential maximum of 1.33 pounds per 1000 cubic feet. Conclusions
1-Food products exposed to commercial fumigations with chloropicrin were apparently undamaged in any way. The foods tested included (1) flour, cocoa, macaroni, rolled oats in paper bags, and lard and butter in 1-pound cartons exposed 1 week to a concentration of 0.8 pound per 1000 cubic feet; and (2) raisins, prunes, nuts in shell, nut meats, lard, and nut margarine exposed in open containers for one week t’oa concentrat’ion of 1.33 pounds per 1000 cubic feet. 2-Germination tests on buckwheat, corn, oats, sunflower, and wheat showed that exposure for 1week t o a concentration of 0.8 pound chloropicrin per 1000 cubic feet had no detrimental effect on the germinating power of these seeds, the germinating power of wheat and buckwheat being even somewhat improved thereby. 3-It should be emphasized that’ the limited experience gained from these few fumigations does not warrant any Jim1 conclusions concerning dosages, method of applicat’ion or effectiveness of chloropicrin against’ various species of insects. Much additional data on fumigation tests under a variet,y of practical conditions must be accumulated before chloropicrin can be correctly and properly evaluated as a fumigant, We believe, however. that chloropicrin has great merit as a fumigant, by reason of (1) the protective warning produced by its lachrymatory power in high dilutions, (2) the fact t’hat it appears not to injure food products or the germinating power of seed, and (3) that it kills or poisons beyond recovery a very high percentage of such insects as the Indian meal moth, Mediterranean flour moth, and the more resistant confused flour beetle in fumigations made on a commercial scale with dosages of chloropicrin ranging from 0.8 to 1.33 pounds per 1000 cubic feet. Bibliography I-Moore,
“Toxicity of Volatile Organic Compounds to Insect Eggs,”
J. Agr. Research, 12, 579 (1917). 2-Moore, “Physical Properties Governing the Efficacy of Contact Insecticides,” I b i d . , 13, 523 (1918). 3-Moore, “Fumigation with Chloropicrin,” J . Econ. Enlomol., 11, 367 (1918). 4-Moore, “Methods of Control of the Clothes Louse,” J. Lob. Clin. M e d . , 3, 261 (1918). h B e r t r a n d , “High Toxicity of Chloropicrin towards Certain Lower Animals,” Compt. rend., 168, 742 (1919) ; C. A . , 13, 1614 (1919). 6-Bertrand and Rosenblatt, “Comparative Toxic Action of Some Volatile Substances on Certain Insects,” I b i d . , 168, 911 (1919); C. A , , 13, 1740 (1919). 7--Ringelmann, “The Struggle against the Field Mouse in the Liberated Regions,” Compt.-Yend. ocad. a g ~ .Fuonce, 5 , 874 (1919); C. A , . 14, 447 (1920). 8-Vayssiere, “The Struggle against the Field Mouse in the Regions Liberated in 1919. Utilization of Chloropicrin,” I b i d . , 5, 885 (1919). 9-Bertrand, Brocq-Rousseau, and Dassonville, “Destruction of Weevils by Chloropicrin,” Compt. rend., 169, 880 (1919); C. .4.,14, 588 (1920). l*-Spencer, “Results of Some Preliminary Experiments with Chloropicrin,” 50th Annual Report, Entomological Society of Ontario, 1919, p. 18.
INDUSTRIAL A N D ENGINEERING CHEMISTRY
464
1I-Bertrand, Brocq-Rousseau, and Dassonville, “Influence of Temperature and Other Physical Agents upon the Insecticidal Power of Chloropicrin,” Comfit. rend., 169, 1059 (1919); C. A , , 14, 588 (1920). 12-Bertrand, Brocq-Rousseau, and Dassonville, “Comparative Action of Chloropicrin on Weevil and on Tribolium,” Ibid., 169, 1428 (1919); C. A . , 14, 1404 (19201. 13-Bertrand, Brocq-Rousseau, and Dassonville, “Extermination of Rats by Chloropicrin,” I b i d . , 170, 345 (1920) ; C.A . , 14, 2046 (1920). 14-Bertrand and Rosenblatt, “Action of Chloropicrin on Certain Bacterial Fermentations,” I b i d . , 170, 1468 (1920); C.A . , 14, 2676 (1920). 15-Guerin and Lormaod, “Action of Chlorine and Various Vapors (Including Chloropicrin) upon Plants,” Ibid., 170, 401 (1920); C. A , , 14, 3415 (1920). 16-Piiitti, “Action of Chloropicrin on Parasites of Wheat and on Rats,” I b i d . , 170, 864 (1920); C. A . , 15, 1593 (1921). 17-Piutti and Mango, “Employment of Chloropicrin in Disinfection of Cereals,” Giorn. chim. i n d . afiplicafa,2 , 677 (1920); C. A , 15, 2523 (1921). 1s-Bertrand, “Action of Chloropicrin on Higher Plants,” Comfit. rend., 170, 858 (1920); C. A , , 16, 1593 (1921). 19-Feytaud, “Destruction of Termites,” Ibid., 171, 440 (192Oj; C. A . 14, 3746 (19201. 20-Burkhardt, “Experiments with Chloropicrin as a Means for Combating Parasites,” Deut. Zandw. Presse, 47, 447 (1920). 21-Neifert and Garrison, “Experiments on the Toxic Action of Certain Gases on Insects, Seeds, and Fungi,” U. S . Dept. Agr., Bull. 893 (1920). 22-Tattersfield and Roberts, “Influence of Chemical Constitution on the Toxicity of Organic Compounds to Wireworms,” J . Agr. Sci., 10, 199 (1920); C. A . , 15, 141 (1921). 23-Miege, “Effect of Chloropicrin on the Germinating Power of Seeds,” Comfit. rend., 172, 170 (1921); C. A , , 16, 1371 (1921). 24--Remy, “Action of Vapors of Chloropicrin on AYgas rcjlexus Fabr.,” Zbid., 172, 1619 (1921); C. A , , 15, 3337 (1921).
Vol. 19, No. 4
25--Wille, “Chloropicrin a s a n Insecticide, Especially for Combating the Grain Weevil (CUlQndYQ granaria),” 2. angew. Entomol., 7, 296 (1921); C. A . , 16, 2962 (1922). 2 G M a t r u c h o t and Sec, “Action of Chloropicrin on Various Fungi,” Compl. rend. SOL. biol., 83, 170 (1920); C. A . , 16, 4003 (1922). 27-Randier, “Chloropicrin,” Arch. med. fiharm. nauales, 122 (JanuaryFebruary, 1922), 22 pp.; Tech. sonit. munic., 17, 226 (1922); C. A . , 17, 1682 (1923). 28-Yamamoto, “Insecticidal Use of Chloropicrin,”Rikwaqaku K e n k r u j o Iho, 1, 1 (1922); C.A . , 17, 2341 (1923). 29-Delassus, “Chloropicrin and I t s Use for the Destruction of Insects,” Rev. agr. afrique nard., 20, 78 (1922). 30-Matthews, “Partial Sterilization of Soil by Antiseptics,” J . Agr. S c i . , 14, 1 (1923); C.A . , 18, 1543 (1924). al-Bertranc), “Suffocation of the Silkworm Cocoon by Chloropicrin,” Comfit. rend., 178, 1656 (1924); C. A . , 18, 2608 (1924). 32-Piedallu, “Destruction of Parasites in Stored Cereals,” Chimie b industrie, Spec. No., 740-2 (May, 1924); C. A . , 18, 3248 (19241. 34-Neifert, Cook, Roark, Toulsin, Back, and Cotton, “Fumigation against Grain Weevils with Various Organic Compounds,” U . S. Dept. A g r . , Bull. 1313 (1926). 3%McDonnell, “Recent Progress in Insecticides and Fungicides,” I n d . E n g . Chem., 16, 1007 (1924). 36-Chapman, “Fumigation Mixture,” U. S. Patent 1,502,174 (July 22, 1924); C. A , , 18, 2937 (1924). 37-Chapman and Johnson, “Possibilities and Limitations of Chloropicrin as a Fumigant for Cereal Products.” J . A g r . Research, 31, 745 (1925). 38-Strand, “Preliminary Experiments on the Use of Chloropicrin as an Insect Fumigant in Flour and Cereal Mills,” J . Econ. Entomol., 19, 504 (1926). 39-Roark, “Chemistry Bibliography No. 1. Chloropicrin,” U. S. Defit. Agr., Bur. Chemistry, 1926.
Influence of Rust-Film Thickness upon the Rate of Corrosion of Steels’ By E. L. Chappell RESEARCH LABORATORY
OF
APPLIEDCHEMISTRY, MASSACHUSETTS INSTITUTE O F TECHNOLOGY, CAMBRIDGE,
?YIASS.
In the absence of rust films different commercial relations have been sought steels corrode in water or in the atmosphere at characbetween corrosion films on a given c o m m e r c i a l steel is commonly obteristic rates determined by the chemical properties of steels and their corrosion rates their surfaces. Copper-bearing steels, for example, under ordinary conditions of served to be dependent upon surrounding conditions, such tend to be more resistant than non-copper-bearing exposure. This paper preas moisture, temperature, etc. steels under any circumstances where a thick rust sents data which indicate the It is almost equally agreed film does not form. conditions under which the that different steels may show The natural course of atmospheric corrosion does not rust films on steels seem to quite different resistances to lead to the formation of heavy rust films, so copperdetermine the corrosion rate corrosion under a given set of bearing steels have been shown by experience to be quantitatively, external facconditions. The recognition superior for this service. Underwater corrosion genertors being constant. ally leads to the formation of a heavy rust film, and of the factors which enter little difference has been found in the corrosion rates Texture of Films in Atmosinto such varying behavior pheric Corrosion of steels under water. Under conditions where some may be hoped to allow the e f f e c t i v e a p p l i c a t i o n of cause, such as abrasion, prevents the formation of a I t h a s b e e n frequently methods of corrosion retardafilm in underwater service, copper-bearing steels would noted that the appearance of tion and to prevent misleadprobably be superior to non-copper-bearing steels. Lhe rust on a highly resistant There is a quantitative decrease in corrosion rate steel exposed to the atmosing conclusions from being about proportional to increases of rust-film thickness. phere differs from that upon drawn in regard to the behavior of steels in tests of a less resistant one. This has led to the belief that resistant steels, such as copper steels, corrosion resistance. The effect of rust-film thickness upon the corrosion of steels build upon themselves a protective rust film. As this theory has been qualitatively recognized.2 The quantitative effects might be advanced as an objection to the suggestions which of oxide-film thickness in high-temperature corrosion394 will be made later in this paper, it will be discussed here. and in the natural corrosion of copper and zincs have been Data previously published from this laboratory6show that the studied. However, it seems that heretofore no quantitative relative rates of corrosion in the atmosphere of resistant and mn-resistant steels may be predicted frorn tests extending 1 presented before the ~ i ~of Industrial i ~ i and ~ Engineering ~ ChemOver Only a few days. I n these rapid tests the steels were istry a t the 72nd Meeting of the American Chemical Society, Philadelphia, Pa., September 5 t o 11, 1926. entirely free from rust when first exposed and the more re2 Speller, “Corrosion,” p. 152, McGraw-Hill Book Co , 1926. sistant ones were frequently only partially covered with rust a Tamman, Rec. frav. chim., 42, 547 (1923). a t the end of the test, while the steels which corroded the 4 Pillings and Bedworth, THISJOURNAL, 17, 372 (1926).
HE rate of corrosion of
T
6
Vernon, Trans. Faraday Soc., 19, 839 (1924).
Whitman and Chappell, THISJOURNAL, 18, 533 (1926).
