~ o v . 1, 9 2 0
T H E J O U R N A L OF I N D U S T R I A L A N D E N G I N E E R I N G C H E M I S T R Y
while boiling. T h e solution is filtered rapidly while hot, and t h e filtrate allowed t o cool. The formation of a crystalline precipitate in the filtrate on cooling does not necessarily indicate the presence of any of the remaining acids, since the pnaphthylamine naphthalene-z,6-disulfonate is not completely insoluble in hot water. However, the presence of other naphthalene sulfonic acids a t this point has a salting-out effect on the 2,6-salt, and hence its precipitation is more complete in hot water when some of the naphthalene sulfonic acids are present whose @-naphthylamine salts are soluble in boiling water (the a-, 1,6- or z,7-acids). When none of these acids are present, the salt separating on cooling is distinctivewhite, fine, and voluminous-and when once seen would never be mistaken for the salts of any of the other naphthalene sulfonic acids not yet removed. TEST F O R NAPHTHALENE-CY-SULFONIC A C I D
The filtrate from the previous test is allowed t o cool and stand a t least one hour after i t is cold t o insure complete crystallization of the difficultly soluble salts. Should a jelly be formed, more water is added, and the solution heated t o boiling and cooled again. The salts are then filtered and dried in a vacuuni oven a t 100' C. The filtrate should be tested with more of the cold reagent t o be sure of complete precipitation. A small quantity of the dry salts is boiled with 2 or 3 cc. of acetone, filtered through a warm, dry funnel, and the filtrate cooled. The presence of a-sulfonic acid is shown i n the cold filtrate b y the separationof crystals of @-naphthylamine naphthalene-a-sulfonate.' If this acid is found, the whole mass of the salts is boiled with acetone, filtered hot through a warm, dry funnel, boiled again with acetone, filtered, and t h e residue washed with hot acetone. T h e insoluble salts are then dried and examined under the microscope. OPTICAL PROPERTIES-Immerse the salts in methyl salicylate or other oily liquid having a refractive index near 1.53. Turn the stage t o bring a clearcut crystal (rod or plate) into parallelism with t h e plane of vibration of t h e polarizing nicol prism (as indicated by one of the cross hairs; which cross hair must be determined in advance). If the crystal boundaries disappear, indicating the identity of refractive index of the liquid with t h a t of the crystal in the direction of elongation; and if, on inserting the analyzing nicol, in crossed position, the extinction is more or less inclined, i. e., if t h e crystal becomes dark when turned so as t o make a n angle of up t o nearly I O ' with a cross hair, the presence of naphthalene-z,7-disulfonicacid as its @-naphthylamine salt is indicated. This salt of the 2,7acid also shows a characteristic twinning habit, the two parts of t h e crystal plates showing extinction in different positions. These twinned plates also show a n approximately 1 2 0 ' termination. If t h e crystal boundaries remain distinct, and, on raising the microscope tube, a band of light appears t o enter t h e crystal, showing t h a t its refractive index 1
See p. 1082 of preceding paper
1087
exceeds t h a t of the liquid in the direction of elongation; and if, on inserting t h e analyzing nicol in crossed position, the extinction is' parallel, i. e., the crystal becomes dark when parallel t o a cross hair, the presence of naphthalene-1,6-disulfonicacid also as the @-naphthylamine salt is indicated. If salts of both acids are present, both behaviors can be readily recognized on separate crystals. These optical properties are very characteristic of these two salts, as may be seen by referring t o the table of optical properties given in t h e preceding article. The very small amounts of t h e salts of any of the other four naphthalene sulfonic acids which may be present a t this point of the analysis do not in any way interfere with these observations, and are readily recognized as impurities. D E L I C A C Y O F THE TESTS
Most of the above-described tests are as delicate as i t is necessary for them t o be when used for technical purposes. The precipitation of the @- and 2,6-acids is very nearly quantitative, so t h a t a rough estimate of the amounts of these present can be made by weighing t h e dried precipitates. The precipitation of the 1,sacid is not so complete, since a-naphthylamine naphthalene-I,5-sulfonate is slightly soluble in boiling water. The a-sulfonic acid salt is almost completely insoluble in cold water, and by evaporating t h e ace;tone extract, its weight may be obtained, since none of the other salts are appreciably soluble in acetone. A rough estimate of the relative amounts of the 2 , 7 and 1,6-salts may be made under the microscope.1 SUMMARY
A method is proposed for the qualitative examination of mixtures of the following naphthalene sulfonic acids: CY- and @-monosulfonic,and I,s-, 1,6-, 2,6-, and 2,7-disulfonic acids.
THE MECHANISM OF BATING2 By John Arthur Wilson LABORATORIES O F A. F. GALLUN&
SONS CO., MILWAUKEE, WISCONSIN Received August 25, 1920
Perhaps the most curious of all the processes involved in making leather is t h a t of bating. Little is known of its origin because i t was a secret process, b u t i t is a t least some centuries old. After t h e skins are taken from t h e lime liquors, unhaired, and washed, they are plump and rubbery, a condition not particularly suitable for putting them directly into the t a n liquors. The object of bating is t o prepare t h e unhaired skins for tanning, and originally consisted in keeping them in a warm infusion of t h e dung of dogs or fowls until all plumpness had disappeared and the skins had become so soft as t o retain the impression of thumb and finger when pinched and sufficiently 1 The authors wish to extend their thanks t o Messrs. G. 0. Oberhelman and D. F. J. Lynch for their kindness in checking and confirming this method, and for suggestions they have made for its improvement. 1 Presented before the Section of Leather Chemistry at the 60th Meeting of the American Chemical Society, Chicago, Ill., Sept. 6 to 10, 1920.
-\
FIG.
%‘
T H E J O U R N A L O F I N D U S T R I A L A N D E N G I N E E R I N G C H E M I S T R Y Vol.
I 088
I-CROSS
GRAINAND PAPILLARY LAYER O F CALFSKIN NOTE ELASTIN FIBERS I N U P P E R HALF. MAGNIFICATION 42 X
SECTION O F
FIG
BATEDWITHOUT TRYPSIN.
porous t o permit the passage of air under slight pressure. I n his book Wood1 says: The object of bating or puering is to render the skins, and the resulting leather, soft and supple. * * * Puering is not only a filthy and disgusting operation, but is prejudicial to health and in the nature of it is attended by more worry and trouble than all the rest of the processes in leather making put together. Wood made a thorough study of dungs and their action upon skins and his final opinion was t h a t the active constituents of the dung infusions were ammonium compounds and pancreatic or similar enzymes. As a result of this work, and some practical development by others, dung has been replaced as a bating material in many tanneries by a mixture of ammonium chloride and pancreatin. Our knowledge of the behavior of proteins in contact with aqueous solutions of acids, bases, and salts, in which the protein swells by absorption of water t o a n extent depending upon the nature and concentration of the electrolyte, raises the question as t o whether bating is not simply a means of bringing the skins into a condition of minimum swelling, especially since such a condition would give the skins those physical properties which are widely accepted as indicative of properly bated skins. If this were so it would reduce bating t o perhaps the simplest of the tannery processes. EXPERIMENTAL
The following experiment was made t o show the comparative degrees of swelling of hide in lime water, in a bate liquor, and in water. I n each of three IOO cc. graduated cylinders were placed 2 g. of “Standard” hide powder. The first was filled with saturated lime water, the second with distilled water, and the third with a bate liquor showing a value for log H+ of -8.1. The cylinders were stoppered and shaken a t 1
“ P u e r i n g , Bating and Drenching of Skins,” Spon, 1912.
2-cROSS
SP,CTION OF
GRAIN AND
BATEDFOR 6 HRS.WITH TRYPSIN.
REMOVED.
PAPILLARY
12,
LAYERO F
No.
I;n
CALFSKTX
ELASTIN FIBERS PARTLY
MAGNIFICATION 42 X
intervals, and the swollen powders allowed t o settle. A t the end of 8 hrs. the volumes occupied by the powders were as follows: in lime water 41 cc., in distilled water 3 2 cc., and in the bate liquor 3 1 cc., showing t h a t the bate liquor actually causes less swelling of hide t h a n ordinary distilled water. A pure solution of ammonium chloride of the same concentration and alkalinity as the bate liquor produces practically the same degree of swelling. A more practical test was made by comparing t h e action of ammonium chloride alone with t h a t of a commercial bate, supposedly containing ammonium) chloride and pancreatin. , B o t h liquors were made u p t o a concentration of 1.20 g. of ammonium chloride per liter, skins of similar nature were put into each, and all other conditions kept as nearly alike as possible. At the end of several hours the skins in both liquors had all the physical properties of bated skins and n o difference between the two lots could be detected, even after tanning. Recently a number of chemists in various parts of the country have informed the author of similar findings. This test would seem t o indicate one of two things-either t h a t pancreatin was of no practical benefit, or else t h a t the commercial bate was deficient in enzymes. Some years ago Rosenthall concluded t h a t t h e bating process removes elastin from t h e skin. I n a sample from the b u t t of a calfskin he found 10.36 per cent of elastin, calculated on the dry basis, before bating, and only 0.31 per cent after bating. But, as a measure of the elastin content of a skin, he used the per cent of nitrogenous matter t h a t could be rendered soluble by tryptic digestion, whereas his bating process was also supposedly a tryptic digestion. What he proved was merely t h a t bating removed almost t o completion certain nitrogenous matter from t h e limed skin, but whether this was elastin or hide substance 1
J . A m . Leather Chem. Assoc , 11 ( 1 9 1 6 ) , 463.
XOV.,1920
FIG.3-cROSS
T H E J O U R N A L OF I N D U S T R I A L A N D E N G I N E E R I N G C G E M I S T R Y
SECTION OF
GRAINAND
PAPILLARY LAYER OF CALFSKIN
BATEDFOR 20 HRS. WITH TRYPSIN.FEWELASTIN FIBERSLEFT. MAGNIFICATION 42 X
which had previously been attacked by lime appears open t o question. The statement t h a t elastin is removed by bating is also made by Moellerl and by Seymour-Jones,2 who in collaboration with Wood carried out a n interesting experiment on the bating of sheepskin. The “flywing” grain of a sheepskin was split from t h e main body of the skin, called simply flesh for convenience, and both grain and flesh were cut into halves along the backbone. One grain and one flesh were bated with pancreatin, while the other halves were delimed with acetic acid, but not bated. All four pieces were then tanned with sumac. There was comparatively little difference between the bated and unbatecl flesh halves, but the grain samples were very different from each other. The bated grain was soft and even, with the hair-holes clean and clear, but in the unbated grain the hair-holes appeared t o be glued up and the surface had a rough, contracted appearance. Seymour-Jones concluded t h a t elastin is present only in the grain membrane and t h a t i t must be digested before tanning t o produce a satisfactory grain, but t h a t bating of the skin under the grain is not only unnecessary, but often undesirable. The results of this experiment may, however, not have been due t o the bating process since one grain had been treated with acetic acid, while the other apparently had not. The author recalls having tanned in the same liquor a bated skin and one both bated and pickled. The difference between the tanned skins was striking, the pickled skin being shriveled t o half of its original area and having a n almost corrugated appearance, while the other had not shrunk a t all and was quite smooth. I t was decided t o settle definitely the question of the removal of: elastin in the bating process by means of photomicrographs of cross sections of the skins taken 1 2
Collegium, 1918, 1 0 5 , 125; Chem. Abs., 12 (1918), 2706. J . Soc Leather Trades’ Chem., 4 (1920). 60.
FIG.4 - c R O S S
SECTION OF
GRAINAND
PAPILLARY
I089
LAYEROF
CALFSKIN
BATED FOR 24 HRS WITH TRYPSIN.ELASTIN FIBERS ENTIRELY REMOVED. MAGNIFICATION 42 X
before and after bating. The elastin fibers are not clearly discernible unless suitably stained, and for this purpose magenta has been found excellent, since it makes the elastin much darker in color, and therefore more prominent t h a n the rest of the skin. Two liquors were prepared, each containing 1 . 2 0 g. per liter of ammonium chloride, while one also contained 0.03 g. per liter of a U. S. P. grade of trypsin. Enough alkali was added t o each t o make the value for log Hf about -8.0. A piece of limed calfskin was kept in each of these liquors for 24 hrs. a t about 3 7 ’ . Microscopic examination of the sample from the trypsin liquor showed t h a t practically all of the elastin had been removed, while, in the piece treated with ammonium chloride only, the elastin was left apparently unaltered. The test was carried out on a large scale with the same result. The time factor in the removal of elastin can be followed by means of the photomicrographs shown in Figs. I t o 4, inc1usive.l The sections, which are all 4 0 p thick, have been stained with magenta t o make the elastin fibers more prominent. I n Fig. 4 the grain membrane shows clearly enough t o be measured, and is about 0.046 mm. thick. The skins are from medium-size calves, and all sections shown were taken from the butt. I n a section 2. j mm:thick t h e elastin fibers were present t o a depth of 0.j mm. from the grain surface, then for a distance of 1 . 7 mm. no elastin could be detected, but was abundant in the remaining 0.3 mm. of flesh surface. This fully confirms the view of Seymour-Jones t h a t the main body of skin contains no elastin. The value of removing elastin from skins must depend t o some extent upon the particular properties desired in the leather, but between skins containing elastin and those from which i t had been removed no such differences as were noted by Seymour-Jones 1 Acknowledgment is made of the assistance of Mr. Guido Daub in the preparation of the photomicrographs.
IO90
T H E J O U R N A L O F I N D U S T R I A L A N D E N G I N E E R I N G C H E M I S T R Y Vol.
could be detected, probably because the differences he found were due t o causes other t h a n bating. CONCLUSION
The mechanism of bating evidently consists of two distinct parts: ( I ) Reducing limed skins t o a condition of minimum swelling; (2) digesting the elastin fibers present in the outer layers of the skins. INCLUSIONS AND FERRITE CRYSTALLIZATION IN STEEL. 11-SOLUBILITY OF INCLUSIONS' By E. G. Mahin and E.H.Hartwig DEPARTMENT O F CHEMISTRY, PURDUE UNIVERSITY, LAFAYETTE, INDIANA
I n a n earlier paper by one of us2 experimental evidence was offered for the widely held theory t h a t nonmetallic inclusions are partly responsible for ferrite segregation in steel, indicating t h a t Stead's view t o the contrary3 may be incorrect. Stead had concluded, as a result of his experiments, t h a t phosphorus segregation about inclusions is responsible for this phenomenon, and t h a t the presence of inclusions has no direct bearing upon ferrite formation from slowly cooled hypoeutectoid steels. The writer, on the other hand, showed t h a t ferrite continues t o segregate about inclusions even after long heating a t temperatures considerably above Ars, although the longitudinal ferrite streaks of rolled steel disappear because of the better dissemination of phosphorus t h a t is brought about by such heating. To account for this definitely established fact, i t was assumed t h a t either the material of the inclusion itself or some reaction product of this with surrounding metal (or both of these) is soluble, t o a slight extent a t least, in iron or in austenite, and t h a t the presence of this dissolved material so alters solubility relations as t o cause the beginning of ferrite separation from austenite in the regions so penetrated, before supersaturation has broken down a t other points. The mechanism of the breakdown of the solid solution of hypoeutectoid steel is somewhat as follows: As the steel cools slowly through the transformation range, the austenite of higher temperatures becomes saturated with ferrite a t the ideal temperature, As. Ferrite does not, in any case, separate at this point, but remains in solution until a somewhat lower temperature, Ar3, is reached, when the supersaturation then existing can no longer be maintained. When ferrite separation begins, recalescence occurs, and austenite continues t o reject ferrite about the crystal nuclei thvs formed until the temperature has fallen t o An, when austenite of eutectoid composition remains and is changed bodily t o pearlite. However, i t is not t o be supposed t h a t the degree of supersaturation of ferrite in austenite is the same in all parts of the steel mass, or even in a11 parts of a given austenite grain. Austenite of absolutely uniform concentration is a n ideal substance, probably never existing in a given steel mass. Even if all elements but carbon and iron could be excluded, such uniformity could be approached only in steel cooling from the li1 Read
at the 59th Meeting of the American Chemical Society St.
Louis, Mo,, April 12 to 16, 1920. a Mahin, THISJOURNAL, 11 (1919). 739. a J . Iron and Steel Inst., 97 (1918), 287, 389.
12,
No.
IS
quid state, because when a cooled hypoeutectoid steel is reheated, reabsorption of ferrite by austenite, as t h e transformation range is traversed, gives austenite grains containing more iron carbide toward their centers and more iron in t h e outer portions and, while diffusion is a fairly rapid process, i t is not likely t h a t any ordinary heating entirely serves t o correct this lack of uniformity in concentration. It is therefore in the regions of higher iron concentration t h a t supersaturation during cooling is greatest and, leaving other influences out of account, i t is in these regions t h a t t h e nuclei of ferrite grains are first gerierated. It is a general condition t h a t if a third substance is added t o a binary solution which is already saturated with one of its components, the solubility of this component is lowered. The opposite is sometimes true, and in certain cases of ordinary solutions the presence of the third substance has little observable effect, but these cases are exceptional. I n the binary solid solution, iron-iron carbide, the nonmetallic inclusion or a reaction product may be regarded as the third substance. It is not necessary t o assume a large solubility for this third substance. If there is a zone, however narrow, lying about a n inclusion and containing even a trace of some third dissolved substance derived from t h e inclusion itself, the presence of this material should alter the solubility of ferrite in the austenite there present, and thus cause local breakdown of the cooling solution first in these regions. This would establish ferrite nuclei, and separation would continue a t these points. The cooled steel would then show inclusions embedded in ferrite. One reaction product was suggested in t h e first paper. This was manganese, an equilibrium product resulting from contact of manganese sulfide inclusions with iron. It would appear t h a t t h e steel in contact with such a n inclusion must necessarily contain manganese in slightly higher concentration t h a n in other regions. This would also be true of manganese sulfide itself and of ferrous sulfide existing in equilibrium with t h e other substances involved in t h e reaction. Similar reactions are conceivable in the case of oxides, silicates, sulfides, etc., of elements other than iron, a n d the reaction products, as well as the original inclusions, must dissolve t o a slight extent in the surrounding metal. I t was earlier pointed out t h a t the effort t o produce artificial inclusions by sealing powders into holes in steel could not be expected t o produce any very definite results, because air could not be entirely excluded from such cavities, and the film of oxide produced on the lining of the cavity when t h e steel was heated must prevent intimate contact with t h e inclusion, even if the latter were fusible. Of nine materials used by Dr. Stead, a t least five (calcium fluoride, calcium oxide, magnesium oxide, silica, and manganese sulfide) would be infusible, or practically so, a t 1000' C., the temperature employed. The difficulties attending the production of intimate contact of artificial nonmetallic inclusions with surrounding metal are not encountered if metallic inclusions are used. Clean holes may be drilled in the steel, and clean, tightly fitting rods of a different material
-
