INDUSTRIAL A N D ENGINEERING CHEMISTRY
February, 1927
of water-soluble matter is doubled, while that of salt-soluble matter is somewhat diminished. With cured skin, the addition of salt to the solution has almost no influence upon the amount of nitrogenous matter extracted.
251
Acknowledgment The author desires to thank John Arthur Wilson for many suggestions received during the preparation of this paper, and for permission to publish.
Influence of H-Ion Concentration and Valency of Added Anion on Plumping in Tan Liquors' By R. 0. Page and J. A. Gilman WOOLSTON TANNERIES,WOOLSION, NEWZSALAND
REAT importance has always been attached to the plumping effects of tan liquors in sole leather tanning. The numerous attempts2 to measure this property directly by determinations of the gain in weight of hide powder under standard conditions have proved unsatisfactory. Wilson and Galluna measured the apparent thickness of bated calfskin before and after plumping with a thickness gage pressing on the skin for a fixed length of time under constant pressure. This method has been studied by Porter,' who obtained consistent results with calfskin and split and unsplit cow hide, provided samples of uniform thickness were selected. I n the investigation here reported the method of Wilson and Gallun was used, with the exception that, in order to follow more closely the changes in plumping under actual tannery conditions, pieces of hide that had been soaked, limed, unhaired, and I! fleshed were used as the standard instead of bated hide.
G
EQUIVALENT PER LITERO F ACID
Mm. 0.00 0.01 0.02 0.03 0.04
1
Experimental Methods Pieces cut from the butt of a cow hide were soaked in fresh water, limed in a saturated lime solution containing excess lime and 0.1 per cent of sodium sulfide, unhaired, and fleshed. They were then shaken in distilled water for one PH hour. The initial thickness was measured with a sensitive gage pressing on the piece of hide for two minutes under constant pressure. The pieces were shaken with water t o restore their normal shape, and then put into 200 cc. of a solution of wattle bark extract containing 25 grams of solid matter per liter, to which were added varying quantities of sulfuric, hydrochloric, or lactic acid. After 24 hours the thickness was remeasured, and the final pH value of the liquor was determined electrometrically. TI:
A C I ~
Experimental Results The effect of the addition of the acids is shown in the accompanying table. The gage readings are the mean of at least three determinations. 1 Presented before the Division of Leather and Gelatin Chemistry at the 72nd Meeting of the American Chemical Society, Philadelphia, Pa., September 5 to 11, 1926. * Claflin, J . A m . Leather Chem. Assoc., IS, 234 (1920). 8 THISJOURSAL, 16, 376 (1923). J . A m . Leather Chem. Assoc., 20, 282 (1925).
GAGSREADINGS
~ ~ i ~ i Final ~ l
0.05 0.10 0.25
4.75 5.03 5.10 5.12 4.77 5.02 4.98 4.90
0.01 0.02 0.02 0.03 0.03 0.04 0.05 0.10 0.25
4.92 4.85 5.15 5.20 5.07 4.85 5.00 5.08 4.75
0.01 0.02 0.03 0.04 0.05 0.10 0.25
4.75 6.37 4.85 5.22 4.93 5.33 5.12
Ratio
FINAL PH VALUE
Mm.
Sulfuric Acid 4.51 4.85 5.05 5.61 5.37 5.77 5.63 5.35 Hrdrochloric Acid 4.75 4.80 5.97 6.14 6.03 6.01 6.36 6.11 5.39 Lactic Acid 4.56 5.29 4.85 5.33 5.27 6.08
5.99
0.95 0.96 0.99 1.09 1.12 1.15 1.13 1.09
4.80 3.35 2.67 2.35 2.06 1.92 1.34 1.00
0.96 0.99 1.16 1.18 1.19 1.24 1.27 1.20 1,13
3.81 3.40 2.45 2.32 2.20 1.89 1.72 1.08 0.74
0.96 0.98 1.00 1.02 1.07 1.14 1.17
3.97 3.65 3.40 3.06 2.94 2.67 2.41
The ratio of the final to the initial gage reading, which is a measure of the degree of plumping, is plotted against the final pH value for each of the three acids used in the accompanying graph. The weight and volume changes of the test pieces were also determined. They were not sufficiently sensitive or concordant to give reliable results, however. Neither the change in weight nor the change in volume distinguishes between liquor mechanically held between the fibers and that responsible for the swelling of the fibers. The latter is a measure of the plumping. The three curves show a slight increase in plumping with increasing acidity from the isoelectric point up to a pH of about 3.5, then a rapid increase to a maximum a t a pH of 1.8 or rather less, and then a steady decrease in swelling with further reduction in the pH. The curve for lactic acid is practically identical with that for hydrochloric acid over the pH range covered by both curves. The curve for the plumping in the bivalent sulfuric acid is only about half as high as that for hydrochloric or lactic acid. The curves bear a striking resemblance to those obtained by Loeb6 for the swelling of gelatin in pure acid solutions. In his results the swelling was plotted against the pH of the gelatin solution, giving a maximum swelling at a pH of 3 to 3.2. Here of necessity the plumping is plotted against the pH of the external solution, which is lower than that of the hide, giving a maximum plumping a t a pH of about 1.8. Otherwise the two sets of curves are very similar in form. The absolute values of the plumping obtained by this method depend on the plumping in the limed condition, a value which it may be difficult to standardize for different 8
J . Gen. Physiol., S, 247 (1920).
252
I S D r S T R I A L A S D EA-GI-l-EERIaYGCHE-VISTRY
laboratories, but which attracts much interest in works practice. The results obtained would indicate the possibility of getting consistent determinations of the volume changes of the hide fibers under conditions closely approximating those in full-scale operations. Conclusions
The plumping of limed hide in tan liquors may be satisfactorily determined by the method of Wilson and Gallun.
1-01. 19, s o . 2
In any given liquor this plumping is determined by its pH value and the valency of the anions present. The degree of plumping rises with decreasing pH from a minimum at the isoelectric point to a maximum a t about pH 1.8 and then drops rapidly with further lowering of the pH. The maximum plumping for sulfuric acid where the anion is bivalent is about half that for hydrochloric acid with a monovalent anion.
A Study of Gelatin Viscosity and Related Problems‘ By M. Briefer and J. H. Cohen ATLANTICGELATINE CO., W O E U R N , M A S S .
I S C OS1 T Y measureFollowing a discussion of the structure of gelatin, of estimating the performance a study is made of the effect of temperature on the of gelatin in practice would ments of gelatin sohtions are usually made viscosity of gelatin solutions with time of standing. be much simplified. The two under conditions choseneither Consideration is given to the effect of agitation on visf a c t t o r s are, however, funca t random or for reasons of cosity. Solution equilibrium and concentration q u i t i o n s of different physical convenience. Such measurelibrium in their relation to viscosity are defined and disproperties, or a t least of difcussed. The several phases of the gel-sol condition are f e r e n t s t a t e s of the same ments are, of course, of local value only; they are not cornstudied in detail. property, according as one parable with measurements in Viscosity measurements are made under varying conwishes to choose from among other localities and rarely ditions of time, temperature, and concefltration, and the several theories on the the results are applied to practical viscometry. structure or constitution of with those in the published literature. gelatin jellies. The Edible Gelatine Research Society has developed proA reasonable conception of what takes place during the cedures for both jelly strength and viscosity measurements process of swelling, melting, and setting of gelatin-water in the hope of standardizing the conditions under which the mixtures is quite possible from our present knowledge of work is to be done.2 A standard capillary tube viscometer colloidal behavior, so well advanced by eminent investigators together with a calibration curve for each instrument is of recent years. The miters have therefore discussed available. For jelly strength determinations the Bloom briefly the conditions governing and affecting viscosity and gelqmeter has been adopted. The viscosity measurements outlined their conceptions relative to the structure of gelatin reported and discussed in this PaDer were first undertaken as jellies. a review of the standards proposed by the Edible Gelatine Structure of Gelatin Jellies Research Society. The work has since been expanded, however. It is always interesting to note in what manner the obvious All scientific research must finally be translated into terms facts of natural phenomena of sensible proportions relate of practical value or else remain a laboratory curiosity. to the microscopic divisions of substance. As a general Moreover, it must be determined in so far as possible to what proposition, aggregates of matter of sensible mass assume extent the results of laboratory experiments are effective in roughly the form and structure of their microcomponents. general practice. For example, it will be shown that Loeb’s’,* This must proceed from the fact that the physical properties conclusion relating to changes of viscosity with time and of bodies are but multiple effects of the physical properties temperature does not hold for gelatin solutions of appropriate of the units of their composition. Thus, Proctor2 reminds concentrations and temperatures. If this is true, then prac- us that the connective tissue consists of fibers, which in turn tical viscometry requires, and may employ, conditions such are made up of small fibrils of about 1 p in diameter; and that the effects described by Loeb are negligible. B ~ r r e t tfrom , ~ a study of the work of Zsigmondy and others, The viscosity of gelatin solutions is of sufficient importance as well as from his own researches, concludes that the real in manufacture to warrant close attention. The choice structure of gels is a fibrillary network, at first amicroscopic, of time, temperature, and concentration must be such as and later becoming ultra-microscopic, and further that by will best indicate the differences between various grades appropriate experimental conditions it may be made to inand kinds of gelatin. It is obvious, also, that these differ- crease in thickness until a diameter exceeding 1 p has been ences should have as large a value as possible, consistent with reached. Loeb4 has shown that suspensions .of powdered good practice, in order that specimens of nearly equal value gelatin and gelatin in solution (sub-divisions of the larger may be clearly differentiated. aggregates) have reciprocal relations with respect to the If jelly strength and viscosity were interdependent-had influence of eledrolytes on the viscosity and osmotic pressure, some specific numerical ratio one to the other-the problem and it has been shown by one of the writers6 that the plasticity of nitrocellulose skin or film-a plastic solid about 1 Presented under the title “Some Viscosity Measurements of Gelatin” 0.005 inch in cross section-is a linear function of the tembefore the Division of Leather and Gelatin Chemistry at the 72nd Meeting of the American Chemical Society, Philadelphia, Pa., September 5 to 11, perature, closely approximating a curve of the viscosity of 1926. nitrocellulose in solution. SThese methods are stated in a pamphlet issued and freely distributed To whomsoever these conclusions are acceptable it appears by the society t o its members. clear that an identical form and possibly structure persists * Numbers in text refer to bibliography at end of paper.
V
