368
Ih-DUSTKI.\L .kND ENGINEERING CHEMISTRY
To determine whether this continuous extraction was removing an appreciable amount of other elements which are not customarily removed by the ether extraction, a solution containing 10 mg. of copper per 1000 ml. was extracted for 16 hours. The diisopropyl ether extract was evaporated to dryness and the residue tested with ammonia and sodium diethyldithiocarbamate. S o trace of copper was found. This method allows a coiisiderable economy in the amount of ether required for the extraction.
Summary Iron may be completely separated from an aqueous solutio11 as the chloride by a continuous extraction with ether in the dark.
VOL. 10,zo. 7
The method is convenient and allows a considerable saving in the amount of ether required for the extraction.
Literature Cited (1) Dodson, R. W., Forney, G . J., and Swift, E. H . , J . Am. (?hem. S O C . , 58, 2573 (1936). ( 2 ) Gmelins Handbuch der anorganischen Chemie, Eisen 59B, 8th ed.. p. 298. Berlin, Verlag Chemie, 1932. (3) Lundell, G. E. F., and Hoffman, J. I., ”Outlines of Method* of Chemical Analysis,” pp. 96-7, N e F York, John Wiley & Sons.
1938. ( 3 ) SIcNaught, K. J., Anal?&, 62, 467 (1937). (5) Rothe, J. W., Chem. S e w s , 66, 189 (1892’1. (6) Speller, F. N., Ihid., 83, 124 (1901). ( 7 ) Talbot, H. P., A m . Chern. J . , 19, 53 11897). R E C E I V E.4pril D 8. 1938.
Determining the Corrosion Resistance of Tin Plate The Hydrogen Evolution Test V. W. VAURIO, B. S. CLARK,
&\D
R . H. LUECK, American Can Co., Maywood, Ill.
T
I S cans have a commercial record of many years’ standing as satisfactory containers for fruits and fruit products. However, acid corrosion of the tin plate by fruits (and even by Some vegetables) has always confronted the industry and results in losses due to perforation of the tin plate or the formation of “hydrogen swells,” a term denoting a puffed condition in the can caused by a n accumulation of hydrogen. In some years these losses have constituted a very serious economic problem, especially when large portions of the pack have been carried over into the second season. To alleviate these losses numerous investigators have studied the subaqueous corrosion of tin plate and have explained, in part, the mechanics of the corrosion of tin plate by fruit acids. During recent years, the International Tin Research and Development Council under the direction of D. J. McSaughton has published several papers (4, 5 , 6 ) which bring this knowledge up t o date. This organization has built upon the foundation laid by Evans (a),Mantel1 ( I O ) , Lueck and Blair (Q), Kohman and Sanborn ( 8 ) , Morris and Bryan ( I I ) , Culpepper and hIoon ( I ) , and many others. An excellent monograph on tin-can corrosion has been prepared by Hirst and Adam ( 3 ) . The investigators have explained that the tin coating protects the steel base of the tin plate electrochemically, because tin is anodic to steel in most food acids. (The references cited show that the relative potentials of the Fe:Fe-- and Sn:Sn-+ half cells have little to do with the electrochemistry of tin and iron in a can of a n acid food product.) Previous workers have also shown that many materials act as powerful accelerators of corrosion. They have studied the effect of packing variables and storage conditions on service life and have shown that different lots of tin plate vary considerably in rates of corrosion in acids. These investigations indicate that the fruit packer may lengthen the average service of his cans in the following ways : 1. By use of cans made of so-called tvpe L, or low metalloid cold reduced steel. 2. By use of cans made of tm plate carrying heavier tin coat-
ings. This is often uneconomical because of the increased cost of the containers. 3. In some cases by adequate washing of the raw fruit to eliminate spray residues and by use of sulfur-free sugar for sirups. 4. By reducing the oxygen content of the can by ”exhausting” the can, either thermally or mechanically. 5 . By maintaining a reasonable head space in the can. This provides a hydrogen “reservoir.” 6. By cooling the cans with xater after processing. 7 . By storing the cans at cool temperatures. This is not always possible and is frequently costly. I n spite of the improvements in canning technic, the canning industry has been troubled with excessive losses due to the early appearance of hydrogen swells which could not be explained on the basis of poor cannery practice, poor can manufacture, or poor can closure. These more or less sporadic cases of short service life have been traced to tin plate having a lo^ resistance to acid corrosion. Unless the small percentage of tin plate responsible for early hydrogen springer formation can be eliminated, fruit packers will continue to be confronted with corrosion losses. The need for a simple corrosion test that will permit reasonably accurate predictions of can service life and can be applied to commercial shipments of tin plate is obvious. Such a test, based on the rate of hydrogen evolution, under standard conditions, from formed samples of tin plate, was devised in 1932 to measure the difference in corrosion resistance of yarious lot’s of tin plate and is the subject of this paper. It has been used satisfactorily as a routine control test of commercial shipments of tin plate since that time. An accelerated corrison test, in which one or more of t h e factors affecting corrosion has been intensified, cannot be safely used to predict “can service value” under commercial conditions until the test values have been definitely correlated n i t h the actual commercial service values. The accelerated corrosion test devised in these laboratories (the “hydrogen evolution test”) has been proved by many thousands of correlating tests with plain (unlacquered) cans packed with such products as peaches, pears, Royal Anne cherries, and dried prunes in sirup, so that it is possible to predict with reasonable accuracy the service life to be expected from a
JULk 15, 1938
ANALYTICAL EDITION
tested lot of tin plate when made into cans and packed with these products. These correlations are described below.
Definition of Terms
HYDROGEN EVOLUTIOX VALUE. "Hydrogen evolution value" is a measure of the corrosion resistance of a tin-plate specimen subjected to the hydrogen evolution test and is defined as the time in hours required to produce 5 cc. of gas by the action of S hydrochloric acid on a die-formed specimen of tin plate in the apparatus and under the conditions described below. TABLE I. HYDROGEN ET oLUTIOS Samples per Sheet Tested
bheet Yo
1 2 3 4 5
Die-
formed 19 19
18 24 24
Flat dish 21 21 17 21 21
V.4LCE
Average Evolution Hydrogen 1 due
Die-
formed Hours 19 3 23 0 36 7 48 8 52 9
Flat disk Hours 51 9 48 2 52 9 68 8 6Y 6
Difference Hours 32 6 25 2 16 2 20 0 10 7
%
169
110 44 1 41 0
31 6
Cas SERVICEYALEE. For the purposes of this paper, "can service value" of tin plate with respect to a given food product is a measure of the resistance to corrosion losses of a set of cans made from any one lot of tin plate. Plain cans, size Yi2,are made from a given lot of tin plate, packed with the food product, and stored at 37.78' C. (100' F.). Sets of 50 to 100 cans are thus prepared and stored and the time in months required for 50 per cent of the cans to swell because of hydrogen pressure is defined as the can service value.
369
hydrogen springers and perforations is usually localized on the ends, especially a t the areas where the drawing strain is greatest. This is particularly true of the end stored down, which is in intimate contact with the can's contents. The plate in the cylindrical body of the can, except a t the double bend a t the side seam where the metal has been strained, is not usually corroded to the same degree. Stamping and bending the tin plate result in a n increase in porosity (7) and also cause fractures in the tin coating. Hydrogen evolution values with die-formed specimens are lower than those obtained with flat disk samples of any given lot of plate. Furthermore, the percentage difference is larger on plate of low corrosion resistance than on plate of high corrosion resistance. In other words, hydrogen evolution values on die-formed samples evaluate tin plate more satisfactorily with respect to corrosion resistance than do hydrogen evolution values on flat disk samples. This is illustrated in Table I.
Corrosion Medium The corrosion medium is 1.000 N c. P. hydrochloric acid. This is stored a t 48.9" C. (120" F.) in vented 20-liter (5gallon) bottles for 96 hours to assure equilibrium with reference to dissolved air content. Hydrochloric acid was adopted for the corrosion medium in order to obtain more rapid corrosion, so that routine tests could be completed in a reasonably short time. Citric acid behares like hydrochloric, but the corrosion rate is very much slom-er.
dpparatus The corrosion cell, shown in Figure 1, consists of an open-bottom, glass bell-shaped unit, A , of 500-cc. capacity, provided with a ground-glass flange to which is clamped the test specimen, E, which is formed with a die having the same profile as used on a standard sanitary can end (6.7-cm., 2i]/16-inch diameter). Special rubber gaskets, X, form the seal between the glass unit and specimen and between floating ring b and flange of glass vessel A . The bronze base, B , consists of three partsc, a threaded disk countersunk to take the sample; b, a floating ring over a rubber gasket on the glass flange; and over this a threaded ring, a, which screws onto disk c and clamps the whole unit together. 2 is a spanner wench fastened to a table. An olive-tip gas eudiometer, sealed at the top by means of a glass plug, G, is attached to the glass unit, A , as indicated, to collect evolved gas. OverfloJj- tube D is a reservoir for acid displaced by the gas evolved by corrosion. The apparatus is similar in principle to that described in 1936 by hlorris (If). The essential difference is that Morris tested flat disk specimens, TT-hereas the specimens used in the above apparatus are die-formed a5 in commercial use. The necessity for using die-formed test specimens rather than flat disk specimens to measure the acid corrosion resistance of tin plate is apparent from examination of hydrogen springers in commercial fruit packs and of hydrogen evolution values on die-formed specimens compared with hydrogen evolution values on flat disk specimens. Examination of thousands of hydrogen springer cans of commercial fruit packs has shown that corrosion responsible for
B A t L L l T E PLhTE
FIGURE1. COMPLETE HYDROGES EVOLUTION TESTUNIT
370
INDUSTRIAL AND ENGINEERING CHEMISTRY
Procedure The assembled units are filled with acid by gravity flow through the overflow tube shown in Figure 1. The glass plug in the Bunsen valve at the top of the eudiometer is removed to permit displaced air to escape during filling. Acid flow during filling is adjusted to permit free escape of displaced air from the unit.
FIGURE2. TTPICALHYDROGESEVOLUTION CURVES
VOL. 10, NO. 7
RUBBERGASKETS.The accelerating effect of sulfur is well known and precautions are taken to desulfurize all gaskets just prior to using. The standardized procedure for this is described above. Early in the development of the test it was discovered that different types of rubber produced different rates of corrosion on adjacent test specimens cut from the same sheet of plate. To eliminate this variable, a special rubber formula was developed for the gaskets. Since the composition of the gaskets is such an important factor, standardized gaskets from only one source are used. (At present, special standardized hydrogen evolution gaskets are distributed by Wilkens-Anderson Co., Chicago, Ill.) OXYGEN CONTESTOF ACID. Since it r a s found impractical to eliminate the dissolved air completely from the corrosion medium, the oxygen content is controlled by maintaining a constant elevated storage temperature. The acid is stored at 48.9" C. (120" F.)in 20-liter (5-gallon)bottles whichare vented for 96 hours and then stoppered. This procedure controls the dissolved air content sat ii:f actoriIy. QULITYOF WATERUSEDTO MAKEUP THE ACID. Triple-distilled water has been adoDted because single-distilled water from many sources contains minute quantities-of some unknown accelerating agent. VIBRATIOT OF UNITSDURING TEST. The corrosion rate can be increased by continuous vibration which loosens the small bubbles of hydrogen forming on the cathodic surfaces. Vibration i 3 kept to a minimum with the aid of rubber hose couplings to the circulating pump and shock absorbers on the constant-temperature bath.
Typical Results The filled units are placed to a depth of 14.375 cm. (5.75 inches) in a constant-temperature bath a t 57.22" C. (135' F.). A 0.3-cm. (0.125-inch) film of crystal oil over the water aids in maintaining the temperature by decreasing the amount of evaporation. The room temperature is maintained a t 48.9" C. (120" F.), giving a differential in temperature between the eudiometer and the glass base sufficient to provide a gentle agitation of the corroding medium by convection currents. This was found to be necessary t o assure uniform results. When tests were conducted in a room with no differential in temperature between buret and glass base, the rate of corrosion was slower than when a temperature differential was maintained. h room temperature of 48.9' C. (120" F.) was designated because of the impracticability of maintaining lower temperatures throughout the year in all laboratories which were using the hydrogen evolution test.
PRECAUTIONS. All glass ware is thoroughly cleaned with water. Rubber parts including gaskets are desulfurized by boiling in 5 per cent sodium hydroxide for 1 hour, followed by thorough rinsing and subsequent boiling for 10 minutes in N hydrochloric acid to remove traces of cawtic. They are then rinsed and stored under distilled water until used. Fresh gaskets are treated each day and no gaskets which have been held under distilled water for more than 24 hours after treatment are used. Test specimens are thoroughly cleaned of palm oil and dust with suitable solvents-chloroform, ethyl acetate, and the like-followed by a light buffig with a clean, soft cloth. The glass unit, is clamped to the metal base with the maximum possible screw pressure. Assembled units are tested for leaks with 258 mm. (5 pounds) air pressure prior to filling. Filled units are kept in the constant-temperature bath a t 57.22 * 0.27" C. (135 * 0.5" F.) until 5 cc. of gas have evolved. Volume measurements are made a t 2-hour intervals. I n routine tests correction of gas volumes to normal temperature and pressure is unnecessary. The following points of technic must be adhered to closely in order to obtain significant values: TEMPERATURE. The temperature of the water bath is maintained at 57.22 * 27" C. (135 * 0.5" F.) by meansof asuitable thermoregulator. The bath is enclosed in a constant-temperature room controlled to 18.9 * 0.6' C. (120 * 1.0" F.). NOR~L~LITY OF ACID. Variation of 0.2 per cent in concentration does not cause noticeable variations in corrosion rate.
Typical hydrogen evolution curves are shon-n in Figure 2. An induction period, during which gas is evolved very slowly although tin is going into solution, is followed by a sudden change in slope when the rate of hydrogen production is materially increased. This change in slope usually takes place when about 5 cc. of hydrogen have been evolved. The better the tin plate from a corrosion-resistance standpoint, the longer is the induction period. It is during this period that the tin is giving its protection to the base steel.
2
4
6
8
10
,Z 14 1G I8 20 22 24 2G 2 0
--TIME
IN M O U l H 5 -
FIGURE3. TYPICAL VACFUNLOSSCURVES Individual S o ?'/z
cans of peaches, stored at 37.78' C. (100' F.)
From the above it is apparent that the 5-cc. value is a critical one, representing the beginning of rapid corrosion of the plate, and i t therefore becomes the base on which the hydrogen evolution test is established. Most cans packed with California fruits show the same type of behavior. There is a period of induction with a fairly small vacuum loss as indicated by "flip" vacuum tests, followed by rapid loss in vacuum and shortly afterward b y enough internal pressure to make the can a "springer" or a "swell" (Figure 3). (The "flip" vacuum is the external vacuum necessary to cause the end to snap out. This is measured by means of a device consisting of a shallow chamber, which can be fitted snugly to the top of a can and evacuated with a pump. The chamber is fitted with a suitable vacuum gage and release valve.)
JULY 13. 1938
ANALYTICA4LEDITIOS
TABLE 11. CAN SERVICE VPILVE
.kT
DIFFERETT STOR-IGE
TEMPERdTURES
Product Peaches
R_ n v_a_. _ "l ......-
cherries Apricots Grapefruit Prunes in sirup Strawberries Loganberries
C a n Service Value 37.78' C. 2 6 . 6 7 ' C . I.5.5Bo Type of C a n (100' F.) (80' F.) (60' F. Commercial Cans Plain 1.0 1.7
F.
Plain Plain Plain Plain Enameled Enameled
1.0 1.0 1.0 1.0 1.0 1.0
2.0
2.0
...
2 0
...
7.8
1.5 1.8
3.8 3.6
...
21.11' C . (70' F.ja
Cans from Plate of Known Corrosion Resistance Dried prunes in sirup Less t h a n 35 hours H o t rolled 1. O More t h a n 35 hours H o t rolled 1.0 More t h a n 47 hours Type L 1.0
2 la
...
...
1
Gb
2.3b 4 Ob
California warehouse, mean temperature 21.11' C. (70' F.). b American C a n Co. data. T h e other, figures are unpublished d a t a of t h e Western Branch Laboratory of t h e National Canners' Association supplied by the courtesy of G. S. Bohart. a
Determination of Can Service Value The following outline briefly summarizes the steps followed in making the different experimental packs : 1. The tin plate is sorted into lots according to steel manufacturing and composition variables, and each sheet is marked with a suitable code identifying the lot and individual sheet. This code is applied in such a manner that it appears on each part-that is, top, bottom, and body-f each can made from that sheet. 2. The tin plate is made into cans in sets, one sheet of plate from each lot comprising a set. Thus, if ten lots of tin plate were being studied, each set would contain one can from each lot. The sequence of the cans in the sets themselves is carried through all can-manufacturing, can-packing, and can-closing operations, so that the influence of any manufacturing or canning variables will be the same on each lot. Manufacturing operations are under constant supervision, so that the finished can will consist entirely of plate from the same original sheet. This eliminates the sheetto-sheet variations found in tin plate. 3. No. 2l/2 cans 11.6 X 12.7 cm. ('&'/lo X 41'/16 inches) have been used for two reasons: The bulk of commercial packs of California fruits is in this size, and the S o . 2Pz can i* best adapted to the flip vacuum test for studying the loss in vacuum by hydrogen formation. 4. The cans are packed in a commercial cannery in sets in the same sequence in which they are manufactured. This procedure distributes any fruit or canning variables equally among all lots. Constant vigilance is required to keep the cans in the proper sequence, so that when they are closed the code on the can cover coincides with that on the can body.
371
5 . The completed pack is then transferred to the laboratory for observation. The cans are stored in cases in the same sequence as used in manufacturing and packing, so that small variations in storage temperature d l be manifest equally in all lots. The cases are stored in a thermally regulated room and are inspected periodically for vacuum loss or springer formation.
In all the correlating experiments wit'h plain cans described in this paper, a storage temperature of 37.78' C. (100' F.) was maintained. This temperature is not above the commercial range, since products shipped to tropical countries are subjected to similar storage conditions and the temperatures in some California warehouses exceed 37.78' C. (100' F.) during the summer months. Storage a t 37.78' C. (100'F.) results in shorter service value than storage a t lower temperatures. Usually service value a t 37.78' C. (100' F.) continuous storage is about half of that a t 26.67' C. (80' F.) continuous storage. Recent dat.a indicate that the corrosion resistance (as measured Iiy the hydrogen evolution test) affects the ratio of can service value a t 37.78' C. (100" F.) storage to that at 21.11' C. (70' F.) storage. Table I1 shows the effect of temperature on service value. The cans held a t 37.78' C. (100' F.) have been assigned the service value 1.0 and the service value at the other temperatures is rated accordingly.
Can Service Value-Hydrogen Evolution Value Correlations The residues from each sheet corresponding t o each can in the experimental pack are hydrogen evolution tested. One sample from each sheet was t'aken for the correlations described below. Experience has shown that, for the practical application of the test, one sample per sheet is adequate because the effect of intrasheet variation is minimized when a sufficiently large number of sheets is tested. Figures 4 to 8, inclusive, are correlations of average can service value with average hydrogen value with peaches, pears, prunes in sirup, and Royal Anne cherries.
PEACHES (FIGIZRE-1). Correlations are shown for three different years. Thirty-seven different lots of plate representing steelmanufacturing and steel-composition variables were packed in 1932. Thirty-seven different lots of tin plate were packed in 1933, and seven different lots m r e packed in 1934. Each lot consisted of 50 to 100 cans representing the same number of sheets of tin plate. The curves represent the average hydrogen evolution value of each lot plotted against the average can service value. Low hydrogen evolution values are associated with low can service value and as the hydrogen evolution value increases, the can service value increases. In general, the slope of the curve changes in the range 27 to 35 hours on the ordinate. Below this range, a small increase in hydrogen evolution value is associated
INDUSTRIAL AND ENGINEERING CHEMISTRY
372
with a large increment in can service value. Above this range, the relation is reversed. The identical correlation was not found each year, however. The 1933 peaches were evidently more corrosive than those of 1932 and 1934. That the fruit variable is responsible for the lower can service value of the 1933 pack is borne out by the curves. Two packs were made this year. The
70
Y
> 0
60
YOL. 10, NO. 7
AS pointed out previously, the corrosiveness of a certain typeof fruit varies from year to year and in a shifting Of the correlation CUrw along the storage time axis. I n spite of the fruit variable, low hydrogen evolution values are alwavs associated with 10x7 can service values. Copper in the steel, above 0.10 per cent, results in shorter service life of plain cans packed with Royal Anne cherries and with dried prunes in sirup, but does not substantially affect the service life of plain cans packed with peaches or pears nor does it affect the hydrogen evolution values. This effect of copper is more significant with enameled can packs
i m > K
Y
9
:S O
v 0 2
I-
>
D
=
40
u 4
30
20
6''
2
4
6
8
IO
12
14
16
IS
20
FIGURE 5. CORRELATICX OF CAN EVOLCTIOS SERVICEASD HYDROGEN V.4LUES FOR PEARS AVERAGE
C A N S E R V I C E V A L U E . MONTH5
1933B pack (with different lots of tin plate thanusedin the 1933A pack) was made later in the season than the 1933 A pack and has considerably higher can service OF CANSERVICE AND HYDROGES EVOLUTION FIGURE 6. CORRELATIOX value for a comparable hydrogen evolution value. VALUESFOR PRUNES The reason for this difference has not been determined. PEARS (FIGURE5 ) . This curve shows the correlation found with pears packed in 1933 in 40 different lots of plate. Here again low hvdrorren value is associated with low can service value a i d a break"in thk curve is noted at about 25 hours on the hydrogen evolution scale. PROSES .(FIGURE 6 ) . A similar relationship exists for dried prunes m srup. Packs were made in 1933 (40 lots) and in 1934 (7 lots). This product is one of the most corrosive packed in plain cans and the curves show more scatter than was found with the other fruits tested. Of interest is the 1934 pack correlation which has one point (marked with an arrow) that has much shorter service life t,han would be expected from its hydrogen evolution value. This point represents one lot of tin plate having an appreciable copper content in the steel base (0.15 per cent). Figure 7 was drawn to illustrate the relationship between the rate of hydrogen springer formation and the distribution of the hydrogen evolution values obtained on the same lots of tin plate. These curves were constructed from the data of the 1934 pack of prunes in sirup. Each code represents an individual lot of plate. The solid lines show the per cent of hydrogen springers plotted against time in days, while the dotted lines show the per cent of hydrogen evolution 5-cc. failures (time to produce 5 cc.) plotted against time in hours. It is interesting to note the identical nature of the curves for lots R and SE. ROYAL AKXE CHERRIES (FIGURE 8). Royal Anne cherries were packed in 1934 in seven lots of tin plate. The correlation is very ood and is similar to that found with peaches and pears. One lot ?marked with an arrow) falls off the curve. This is a copperbearing steel-base tin plate, the same one mentioned under prunes.
Limitations of the Hydrogen Evolution Test
As is true with all accelerated corrosion tests, individual values show considerable variation and it is impossible to predict service value on the basis of individual tests. I n spite of the individual variations, fairly accurate predictions of the service value of different lots of plate known to be produced of uniform steel are possible, provided correlating data have shown that variations in alloy content of the steel, such as the presence of copper, do not have a specific effect on service life with the specific fruit tested.
FIGURE 7. RELATIONSHIP BETWEEN RATE OF HYDROGEN SPRINGERFORMATION AND DISTRIBUTION OF HYDROGEN EVOLUTION V.4LUES Prunes in sirup
JULY 15, 1938
A4KAIdY-TIChLEDITIOS
I
,
creased corrosion resistance. This is generally true of the hydrogen evolution test, but the correlation between tin coating weight and hydrogen evolution value is not perfect. Other factors besides weight of tin coating (as measured by the Sellars method, 12) contribute to the hydrogen evolution value. Surface condition and steel base compnsitiori have a very significant bearing on corrosion rate. This will he the subject of a future paper. Figures 9 and 10 show scatter diagram6 and regression curves of the tin coating weight-hydrogen evolution value relationship on cold-rolled strip (type L) and hot-pack rolled plate. The tin coating weight was deterniinerl on a ring 25.8 sq. em. (4 square inches) in area concentric to the test specimen and includes the tin on bot'h sides of the speciinen. Each dot represents an individual determination. Hydrogen eyolution values are grouped in 4-hour intervals and the tin coating weights are grouped in 0.10 pound (2.242 grains per square meter) per base box intervals. In Figures 9 and 10, lines shoving the regression of L on y are given, as well as the more usual regression of y 011 .z. The first is used to estimate the most probable value of L for a given value of 5. The second, showing the regrewion of g on .r, is used to estimate the most proliable value of y for a given yalue of s.
I
ao
TIN
COATING
IN
LE5
373
P E R BASE BOX
FIGCRE 9. HYDROGEN EVOLUTIOS VALUE TIS COATING WEIGHT
..
US.
Hot-pack rolled plate
20
30
of red sour pitted cherries and black cherries, which sholv about four times longer service life with cans made of low metalloid strip steel (type L) having less than 0.04 per cent of copper than is found with cans of the same steel having 0.18 per cent of copper. These data contradict the conclusions of Hoar and Harenhand (j),who contend that the copper content of steel for tin plate should be a t least twice its sulfur content. As with the hydrogen evolution test, this aniount of copper (0.18 per cent) does not affect the service life of enameled cans packed with loganberries. This specific effect of copper has been checked in this laboratory with a number of controlled experimental packs.
Correlation of Hydrogen Evolution Value with Tin Coating The variation in test values on a given lot of plate is due partially to variation in the continuity and thickness of the tin coating and to other surface conditions. It is usually agreed that increased tin coating weight results in an in-
.
.
I
I 100
110
!
140
T I N C O A T I N G IN L e 5
1.60 180 PIK B A I E BOX
200
FIGURE10. HYDROGES EVOLVTIOS VALKEL I S . TIS COATIKG WEIGHT Cold-rolled strip plate
Summary A simple test for the corrosion resistance of tin plate based on the rate of hydrogen formation resulting from the attack of N hydrochloric acid on a standard tin plate specimen is described. Correlations between hydrogen evolution values and can service values of plain cans packed with peaches, pears, Royal Anne cherries, and prunes in sirup indicate that the test gives reasonably accurate predictions of can service value. Certain metallic alloying constituents of the steel base affect the can service value with some foods, but do not show a corresponding effect on the hydrogen evolution value. Copper lowers the can service value of Royal Anne cherries and
374
VOL. 10, KO.7
INDUSTRIAL AND ENGINEERIZG CHEMISTRY
prunes in sirup, but has no effect on t,lie service value of peaches or pears.
Literature Cited (1) Cuipepper and Moon, Canning A g e , 9, 461 (1928). (2) Evans, J . SOC.Chem. Ind., 47, 73-71’ (1928). (3) Hirst, F., and Adam, W. B., Nomograph KO.1, University of
Bristol Research Station, Campden, Gloucestershire, 1937. (4) Hoar, T. P., Trans. Faraday SOC.,30, 472 (1934). (5) Hoar, T. P., and Havenhand, D., J . Iron Steel Inst. (London), 133, 239 (1936).
(6) Hoare, W. E., Ihid., 129, 253 (1934). (7) Hothersall and Prytherch, Ibid., 133, 205 (1936). ( 8 ) Kohman and Sanborn, Canning A g e , 9, 381 (1928). (9) Lueck and Blair, Trans. Am. Electrochem. SOC.,54, 257 (1928). (10) Mantel1 and Lincoln, Canning Age, 7, 847 (1926). (11) Morris, T. N., and Bryan, J. AT., Dept. 3ci. Ind. Research, Food Inyest., Special Rpt. 4, 1932; Special R p t . 44, 1936. (12) Scott, “Standard Methods of Chemical Analysis,” 4th ed., Vol, I, p. 534, New York, D. \-an Nostrand Co., 1927. RECEIVED .%pril l R , 1938.
Relation between Volatile Matter and HydrogenCarbon Ratio of Coal and Its Banded Constituents C. H. FISHER. Central Experiment Station, Bureau of >lines, Pittsburgh. Pa.
Using data from the literature and paying special attention to the petrography, the relation between volatile matter and hydrogen-carbon ratio was studied. Plotting these two values against each other gave two curves, approximated by three straight lines. lnthraxylons (vitrain and clarain) are found on one curve, whereas the other constituents (fusains, attrital matter, durains, and spores) occur on the other. The equations representing these straight lines can be used to relate the volatile matter and hydrogen-carbon ratios of the constituents with moderate accurac:. A more interesting and useful relationship is that between the volatile matter and the square of one hundred times the hydrogen-carbon ratio. Two straight lines result when these are plotted. Vitrains and clarains fall on the shorter line, and
S
EVERAL investigators have noted relationships between the volatile matter and the carbon and hydrogen contents of various coals. Ralston (12) constructed a chart that gives the carbon, hydrogen, and oxygen contents and volatile matter content of carbonaceous materials ranging from anthracites to Kood and plants. Korn (9) and Schuster (14) claim that a linear relationship exists between carbon content and volatile matter, a conclusion that has been disputed by Seyler (15). I n studying the connection between proximate and ultimate analyses, Pallot (11) plotted carbon, hydrogen, and oxygen contents against fixed carbon. Spooner (16) proposed several equations that relate volatile matter and ultimate analyses of coals. Although these relationships may be useful and fairly satisfactory, no distinction was made between the type and proportion of petrographic constituents piesent. IIore recently, Seyler (13, 15) pointed out that the petrographic composition of the coal exerts an important influence on the relation between yolatile matter and carbon and hy-
the other constituents fall on the longer line. Equations defining these lines appl: with fair accuracy to anthraxylons of all ranks and to other constituents from low-volatile fusains to high-volatile spores. Probabl?; most important is the determination of the approximate petrographic composition of coals from proximate and ultimate anal>ses, but the equations should be useful also in ascertaining the quality of isolated constituents and in correlating chemical reactions of coal wTith its rank and petrography. By plotting volatile matter against the sum of the hjdrogen and carbon contents and using these equations, a satisfactory estimate of the petrography can be made in many instances from the proximate and ultimate analyses. drogen contents. Bright coals (chiefly anthraxylon or vitrain and clarain) were characterized by the following formula, where, as later in this paper, V , C, and H represent percentages of volatile matter, carbon, and hydrogen, respectively.
V = 10.61H
- 1.24C 4-84.15
It mas claimed that coals not conforming to this equation (dry, mineral-matter-free basis) contain considerable amounts of banded constituents other than vitrain or clarain and that, therefore, some information as to the petrography of the coal can be obtained from the proximate and ultimate analyses. Other equations relating volatile matter of bright coals with carbon or hydrogen content are:
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Seyler’s (16) logarithmic: H = 2.80 log V 0.95 v7~510)- 0.013 Seyler’s (15) quadratic: H = 0.1292V - 0.00156V2 2.69 C = 0.2997’ - 0.01334V2 90.79 Diederichs’ ( 2 ) : H = V
(
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