January, 1925
I N D U S T R I A L A N D ENGINBERING CHEMISTRY
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Vegetable Tanning’nz By Arthur W. Thomas and Margaret W. Kelly COLUMBIA UKIVERSITY, NEW YORX,N. Y.
Part I-Concentration and Time
Although the tannins in the extract used do not have the same combining weight as gallotannin, nevertheless, despite ICRTAIN results concerning the influence of concentra- the speculative character of basing calculations upon the comtion of a vegetable tanning solution upon the fixation bining weight mentioned, such calculations may sometimes of the tannin by hide substance have been p u b l i ~ h e d . ~prove to be not without value. It is interesting to note that the value of 45.3 parts of tannin I n these papers the technic used was the old Wilson and Kern method,4 but results obtained with the modified Wilson and to 100 of collagen is very closely approximated in the maxima Kern technic,5 where the time of tanning was 24 hours,6indi- of the 2-weeks wattle and quebracho curves. The point of minimum in the 21-weeks cated that longer times of
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powder for 2 weeks and 21 weeks. Portions of 100 cc. of extracts of quebracho, wattle bark, hemlock bark, oak bark, gambier, and larch bark and hide powder equal to 2 grams of dry substance were used. All liquors were electrometrically adjusted to pH = 5. The results obtained are given in Table I and Fig. 1. In Fig. 1 the 24-hour results previously published are included for comparison. As in the 24-hour experiments, the curves rise to a maximum and then fall off, the maxima being sharper with the more astringent extracts. In the case of the very astringent extracts the maximum degree of fixation is found at about the same total solids concentration regardless of the time of contact, while with the less astringent extracts the maximum shifts toward higher total solids concentration. A striking fact brought out by these experiments is the second point of inflection, so sharply shown in the hemlock curves and less sharply though dist’inctlyin the larch and gambier experiments. Wilson7 points out that in the combination of pentadigalloylglucose (gallotannic acid) with collagen, if it is assumed that each digalloyl radical is capable of combining with collagen, then the combining ratio of 340 parts of tannin to 750 parts of collagen is obtained, or 45.3 per 100 parts of collagen. He states further that this is the minimum found in fully tanned leather and that the ratio approaches 90 of tannin t o 100 parts collagen after several months’ contact. 1 Part I presented by M. W. Kelly under the title “The Concentration and TimeFactorsin Vegetable Tannages;” Part 11 presented by A. W. Thomas under the title “Influence of Gallic Acid and of Pyrogallol upon Wattle Tannage’’ before the Division of Leather Chemistry at the 66th Meeting of the American Chemical Society, Milwaukee, Wis., September 10 to 14, 1923. Received October 21, 1924. 2 Contribution No. 460 from the Chemical Laboratories, Columbia University. a Thomas and Kelly, THIS JOURNAL, 14, 292 (1922); 16, 928 (1923). 4 Wilson and Kern, I b i d . , 12,465 (1920). 6 I b i d . , 18, 772 (1921). 5 Thomas and Kelly, Zbsd., 16, 1148 (1923). 7 “Chemistry of Leather Manufacture,” 1923, p. 274. Chemical Catalog Co., New York.
Part 11-Effect of Pyrogallol and Gallic Acid It is generally believed that organic substances that do not convert collagen t o l e a t h e r 4 e., nontans-retard the rate of TABLE I ( A ) Grams tannin fixed by 2 grams hide powder; ( B ) Parts tannin per 100
Total solids Grams/ liter 25 40 60
90 140 190 16 25 40 60
90 130
parts hide substance
(.A.)
2 Weeks
0.907(+)’ 0.751 0.584 0.452 0.416 0.419 0.417(+) 0.582 0.609 0.524 0.475 0.407
20 35 60 76 100 150
0.520(+) 0.658 0.678
15 20 30 80 85 125
0.565(&) 0.668 0.681 0.534 0.401 0.657
0.618
0.555 0.480
(B) T’Vdtlle Bark 45.3 37, J 29.2 22.6 20.8 15.9 Oak Bark 20.8 29.1 30.4 26.2 23.7 20.3 Ouebracho
Larch Bark 26 0 32 9 33.9 30 9 27.7 24 0 Hemlock Bark 28.2 32.9 34.0 26.7 20.0 32.8 Gambier
(.A.)
21 Weeks
(. B_ )
1.262( +) 1.262 1.118 1 010 0 828 0.776
63.1 63.1 55.9 50 5 41.4 38.8
0.430(-) 0.795(+) 0.966 0.930 0,898 0.851
22.5 39.7 48.3 46.5 44 9 42.5
0.649(--) 0 . 9 4 9( f ) 1.029 1,044 0.970 0.971
32.4 47.4 51.4 52.2 48.5 48.3
0.627( -)
31.3 41.3 47,l 46.6 42.8 54.1
::Et 3
0.933 0.856 1.083
a The (+) or ( - ) sign after the weight of tannin fixed signifies a positive or negative gelatin-salt test on the filtrate. b Sample molded.
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1NDUXTRIAL A N D ENGINEERING CHEMISTRY
tannage by organic tannins.8 The literature is barren of data on this point, however, and the work reported here is the first of a series of explorations using various nontans of known chemical nature.
grams per liter (on the upward slope of the concentrationtanning curve) and 40 grams per liter (on the downward slope of the curve). The experiments were conducted also a t two different acidities, pH = 2.0 (the high point of the pHtanning curve) and pH = 4.0 (in the region of low fixation). The results are shown in Tables I1 and I11 and Fig. 2. No physical difference due to the presence of gallic acid was observed, but pyrogallol caused marked changes in the solution and collagen, as noted in the table. TABLE11-EFFECT Gallic acid present Gram None 0.049 0.147 0.245 0.490 0.735 None 0.046 0.137 0,229 0.458 0.686
FIG 1-CONCENTRATION
CURVES (PH = 5 0 ) INTERVALS
FOR
DIFFERENT TIME
A study of the effect of gallic acid and pyrogallol upon tanning with gallotannic acid and wattle bark extract shows some interesting results and indicates that the role played by nontans i s not at all so simple as previously thought. Gallotannic acid was selected because of its known chemical nature and commercial wattle bark extract was chosen for comparison because of its.low nontan content. Tannic Acid
Portions of defatted hide powder equal to 2 grams dry substance were rotated in pint bottles for 24 hours with 1OO-cc. portions of solutions of the same tannin content and hydrogenion concentration but of varying nontan content throughout a given series. At the conclusion of the drumming period the contents of the bottles were filtered and washed in Wilson and Kern extractor^,^ the tanned hide pomders air-dried and then dried in vacuo at 100" C. for 16 hours. The ' I l l increase in weight was 05 l0 15 20 M O I A R COl~CENTRATlONOFF*'DDED ?ION TAN" recorded as t a n n i n FIG. S-EFFRCT OF PRESENCE OF NOXTANS fixed by the hide subUPON FIXATION OF GALLOTANNIN stance. In view of previous experience with the tanning action of tannic acidlgtwo concentrations of tannic acid were used, 15 8
Wilson, J . Am. Leather Chem. Assoc., 16, 374 (1920). Thomas and Kelly, THISJOURNAL, 16, 800 (1924).
Vol. 17, No. 1
GALLIC ACIDON TANNIC ACIDTANNAGS GRAMSTANNIN FIXEDB Y 2 GRAMS DRYHIDEPOWDER Tannic acid concn. Tannic acid concn. 15 grams/liter 40 grams/liter Solutions of p H = 2 0.755 1.325 0.749 1,390 0.716 1,334 0.748 1.384 0.777 1.414 0.739 1.397 Solutions of p H = 4 0.694 0.520 0.691 0.453 0.665 0.421 0.626 0.362 0.584 0.301 0.446 0.287
OF
TABLE111-EFFECT OF PYROGALLOL ON TANNIC ACIDT A N N A G E ~ Pyrogallol GRAMS TANNIN FIXEDB Y 2 GRAMSDRYHIDE POWDER present Tannic acid concn. Tannic acid concn. Grams 15 grams/liter 40 gramdliter Solutions o f g H = 2 None 0.775 1.464 0.767 Rubbery and tough 0.98 Rubbery and tough chunks 2.45 0.729 4.90 Very sticky 1.650 12.25 24.50 Too sticky to manipulate, 0.626 Solufzons of p H = 4 None 0 727 0 441 0 385 0 85 0 595 2 12 0 479 0 324 4 23 0 416 0 427 10 58 Sticky and rubbery Sticky and rubbery 21 20
::fyi 11
i:igy 1
:g:! 1
:';;! ]
a Remarks refer to condition of wet tanned samples.
The marked changes in the physical appearance of the wet tanned powders, due to the presence of pyrogallol, indicate that the collagen underwent a chemical change. This was shown in the dried powders. At the higher concentrations of pyrogallol in the pH = 2 series and in the highest in the pH = 4 series, the dry tanned powders were very dark colored and easily pulverized. Wattle Bark
The effects of the nontans on the action of this tanning extract were determined at pH = 3 and 5 in 100 cc. of solution containing 25 grains of total wattle bark solids per liter. This is the concentration of wattle bark which gives the greatest fixation of tannin at pH = 5 in the absence of nontans under the conditions of the experiments-namely, 2 grams of dry hide powder, 100 cc. of solution, 24 hours' contact, and a t room temperature. The results are shown in Table IV and Fig. 3. TABLE IV-EFFECT ----pH
OF
GALLIC ACIDAND
OF
TANNAGE
PYROGALLOL O N WATTLE
3-----,-pH = Tannin 5---fixed by Tannin fixed by 2 grams dry hide 2 grams dry hide powder Nontan present powder Gram Grams Gram Gallic A c i d
=
Nontan present Grams
...
...
... None 2.00 3.99 9.98 19.95 29.93
... ...
U , 46250
0.8770 1.491
... Pyvogallol
0.963 0.875 0.678 0.746 0.676 0.306
. None 2.02 4.03 8.06 16.13 24.19 34.27
0.496 0.272 0.272 0.438 0.668 0.627 0.489
Perusal of the results demonstrates that the presence of nontans does not always retard the rate of tanning, and that
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" 0. I5
F I G . %-EFFECT
4.3
INDUSTRIAL A N D ENGINEERING CHEMISTRY
January, 1925
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' I 1.0 I ' /.'5 I ' I 2.0 ' " I 2.5 1 MOLAR CONCENTRATION OFADDED ;VON-TAN" O F P R E S E N C E OF N O N T A N S UPON
under certain conditions a nontan may accelerate tanning. The chemical nature of the nontan, the amount present, the amount of tannin present, and the pH of the solution are four factors that may markedly influence the reaction. Although gallic acid retards tanning by tannic acid a t p H = 4 and at two different concentrations of tannic acid; yet a t pH = 2 it slightly increases fixation, then decreases it, followed by a second increase just as it does in wattle tannage a t pH = 3 and 5. On the other hand, although pyrogallol regularly decreases tanning by gallotannin a t a concentration of the tannin of 15 grams per liter and a t pH = 2; yet at the same pH, but a t n higher concentration of gallotannin, it accelerates the degree of tannage when present up to 0.2 mol per liter, above which it effects a marked depression in the tannage. However, at pH = 4 it decreases the tannage up to the same point, beyond which it accelerates it, followed by a second drop, with the exception of the higher tannic acid concentration where the acceleration following the depression is very marked. These effects found for tannic acid tannage at pH = 4 are reflected in the wattle curves a t pH = 3 and 5. Acknowledgment
' I I' 30
FIXATION OF
WATTLETANNIN
The authors are pleased to acknowledge the generous support of A. F. Gallun & Sons Company in this investigation.
Indirect Illumination for the Microscope' By Alexander Silverman UNIVERSITY OF PITTSBURGH, PITTSBURGH, PA.
HE designing of an illuminator for indirect lighting was
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prompted by the desirability of producing shadows between the fibers in white textiles to afford contrast. It seemed that this could best be accomplished by bringing the light from the side. Fig. 1 is the side view of a device made of turned brass. Fig. 2 shows the brass bell, A , silvered or nickel-plated on the inside and blackened on the outside. The bell is 65 mm. in diameter a t the base and 25 mm. high, and is provided with a fibroid handle. Collar B, which screws into the bell, is plated on the outside and blackened on the side facing the objective. The collar is 30 mm. in diameter a t the neck, and a t a distance of 8 mm. from the top begins to flare out until it has a diameter of 48 mm. Total depth of collar, 12mm. Fig. 3 is a bottom view. The collar (not shown) is screwed into the bell and the flange spreads below the lamp, C, a single filament tungsten lamp of 9-mm. glass tubing bent into a ring of 58 mm. outside diameter. The lamp operates normallp0.8 ampere and 22 volts, but one can employ the rheostat for the smaller 0.9-ampere, 13-volt direct-lighting unit described in an earlier article*so that 110-or 220-volt A. C. or D. C. current from lighting or service lines may be utilized, making it unnecessary to use dry batteries or storage cells. Pig. 4 shows the illuminator resting on the stage of a microscope with the objective passing through the hollow collar. For the examination of white textiles, black paper should be laid under the fabric. Where enough cloth is available it is an advantage to stretch it between embroidery hoops and have these drop over the edge of the stage, leaving a smooth, flat layer of the material for examination. When dark cloth is being examined it is better to unscrew the collar, lay the cloth on a white background, and use direct illuminaPresented before the Division of Industrial and Engineering Chemistry at the 68th Meeting of the American Chemical Society, Ithaca, N. Y . , September 8 to 13, 1924. THISJOURNAL, 10, 1013 (1918).
tion. Good results are obtained with magnifications of 100 to 200 diameters. With low-power objectives the method of lighting described above serves well for thread counting.
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The writer has often wondered whether the microscope has had sufficient utility as a sales factor. If a microscope tube were mounted directly on an illuminator like the one described, the salesman could connect it with any lighting outlet when displaying his samples. By placing a properly colored paper under the cloth and resting the illuminator above it, he might make a profound impression on the customer. Furthermore, where price competition is involved in the sale of paper, textiles, or similar articles, the salesman may convince the buyer of the superiority of his product by showing the dealer both samples under the microscope.
