570
I N D U S T R I A L A N D ENGINEERING C H E M I S T R Y
Vol. 17. No. 6
The Ventilating Properties of Leather' By John Arthur Wilson and George 0. Lines A. F. GALLUN& SONSCo., MILWAUKEE, Wrs.
COMPREHENSIVE diameter as the two brass Two factors influencing the comfort of shoes-namely, series of investigadisks used-namely, 3.0 cm. the porosity of the leather and its permeability to tions has been begun I n the center of each disk a water vapor-were found to have widely different values in these laboratories for the hole is cut exactly 1.27 em. in for a number of typical shoe leathers. These factors purpose of determining the diameter which allows an area depend largely upon the amount of oil and finishing relation of the factors which of exactly 1.267 sq. cm. of material applied to the leather. Methods for measurinfluence foot comfort to the leather to be exposed. The ing these factors have been developed which should chemical composition of the leather is placed between materially assist the movement to make shoes more shoe leather. The first findthese two brass disks and set comfortable. ing of major importance in into the cap as shown. A this universally important tightly fitting cork having but previously neglected field was that the discomfort a hole in its center 1.4 cm. in diameter is then inserted. The experienced in wearing shoes made of chrome leather is cork resting on the rim of the bottle effects a water-tight seal. caused by the great shrinkage and expansion of this kind of Some pure sulfuric acid is put into the bottle and then leather with changing relative humidity of the atmosphere.2 bottle and acid, without the cap, are weighed. The cap It may be accepted as generally true that with a drop in rela- containing the leather is then screwed into place and the tive humidity from 100 per cent to zero chrome leathers will whole is placed into an ordinary individual desiccator conshrink about 18 per cent in taining water, and this in turn is submerged in a large Freas area, on an average, and vege- thermostat constant to 0.01' C. The acid inside the bottle t a b l e - t a n n e d leathers only tends to maintain an atmosphere of practically zero relative screw cap with about 6 per cent. Thus the humidity, while the water in the desiccator tends to maintain hole1.4cm.diam. B-D i s k of sensitivity of those prognosti- an atmosphere of 100 per cent relative humidity. The only 1 e a t h e r sandwiched between cators who foretell changes in way that water can pass from the outer humid atmosphere two brass disks weather by the degree of pain to the inner dry one is through the leather. I n order to deeach with a hole exactly 1.27 cm. in their corns is greatly in- termine how much water has passed through the 1.267 sq. creased by wearing shoes made cm. of leather area in unit time, it is only necessary to remove diam. C-Tightly t i w cork with of chrome-tanned leather. the bottle and weigh it with the cap removed. The object hole 1.4cm.diam. D-Bottle of The properties of leather to in removing the cap before weighing each time is to avoid 70 cc. capacity be considered in this paper fluctuations due to the changing water content of the leather may, for convenience, be re- and cork. ferred to as ventilating properFigure I-Apparatus to Measure Rate of Passage of ties. It is well recognized that 1200 Water through Leather f r o m a foot housed in a compartment an Atmosphere of High to One I of Low Relative H u m i d i t y impervious to water and air I lloo{ I cannot be comfortable, and I most people have experienced the discomfort attending the i 1000{ wearing of rubbers for any great length of time. The animal I I I body gets rid of its excess heat through the evaporation of the water of perspiration from the surface of the skin. If the foot is so confined that the perspiration a t its outer surface cannot diffuse away or evaporate, it will become hot and uncomfortable. The perspiration then tends to maintain a relative humidity of 100 per cent in the confined atmosphere. I n order to prevent discomfort, the leather of the shoe must remove water from this inner, humid atmosphere and pass it on to the outer atmosphere of lower relative humidity.
A
7
I
Permeability to Water Vapor
The essential part of the apparatus3 used to measure the power of leather to conduct water from an atmosphere of high to one of low relative humidity is shown in Figure 1. It consists of a small wide-mouth bottle fitted with a screw cap, in which a hole 1.4-cm. in diameter has been cut. The leather sample is cut with a circular .die having the same 1 Presented by J. A. Wilson before the Division of Leather and Gelatin Chemistry at the 69th Meeting of the American Chemical Society, Baltimore, Md., April 6 to 10, 1925. 2 Wilson and Gallun, THISJOURNAL, 16, 268 (1924). 8 The methods and apparatus used to measure both permeability to water vapor and porosity of leather were devised by J. A. Wilson; the measurements of porosity were made by A. W. Bear.
5
20 25 30 35 40 4 Temperature 'C. Figure %Effect of Temperature upon Passage of Water f r o m an Atmosphere of 100 Per c e n t Relative Humidity to One of Zero Relative Humidity through Vegetable-Tanned Calf Leather a n d through Free Space
10
15
INDUSTRIAL AND ENGINEERING CHEMISTRY
June, 1925
Effect of Temperature
I n studying the effect of temperature two series of these pieces of apparatus were set up. In one series the caps contained disks of vegetable-tanned calf leather all taken from the butt of the same skin. In the other series no leather was used, but the holes in the disks allowed free contact of the
1
1 I
400
3.50 F L)
?PO
1
'\
''\,b,
MILLIGRAMS OF WATER PASSED PER 24 HOURS THROUGH 1 . 2 6 7 SQUARE CENTDIETERS OF
571
Disks cut from the same piece of leather as that used in the temperature experiment were employed and the desiccators were all kept in a Freas thermostat a t 25' C. The results are shown in Figure 3 and Table 11. Table 11-Effect of Relative Humidity of One Atmosphere upon Passage of Water i n t o I t from Atmosphere Kept a t 100 Per cent Relative Ilumidityacrossan Area of 1.267 Sq. C m . through Free Spaceand through Leather at 25' C. Ratio Per cent rela- MG WATERPASSED PER 24 H R THROUGH: ~ tive humidity Leather Free space Per cent 360 66 0 236 282 63 20 179 217 66 40 143 134 68 60 91 80 51 78 65 100 0 0 Average 66
The rate of passage of water in both series appears to be a straight-line function of the difference in relative humidity between the two atmospheres, and the ratio of the rate of passage through the leather to the rate of passage through free space appears to be constant a t 66 per cent at all relative humidities. Since this ratio appears to be independent of temperature and of difference in relative humidity, it can be used as a constant characteristic of any given sample of leather. It will be used in this paper to indicate the degree of permeability of leather to water vapor. Relative Porosity
20 40 60 80 100 P e r Cent R e l a t i v e Humidity o f Atmosphere
0
Figure 3-Effect of Relative H u m i d i t y of One Atmosphere u p o n Passage of Water i n t o I t f r o m a n Atmosphere K e p t a t 100 Per c e n t Relative H u m i d i t y through Vegetable-Tanned Calf Leather a n d through Free Space
wet and dry atmospheres over the area of 1.267 sq. em. I n the leather series, all grain surfaces were exposed to the dry and the flesh surfaces to the wet atmosphere, as would be the case in the wearing of a shoe. The desiccators were placed in thermostats at different temperatures and the bottles were weighed once each day for a week. The gain in weight per day varied only very slightly throughout the week. The results are shown in Figure 2 and Table I.
In order to show whether any relation exists between the permeability factor and the degree of porosity of leather, measurements of the latter were made with the apparatus pictured in Figure 4. The disk of leather used in the permeability measurements was transferred, in each test, to the vacuum
Table I-Effect of Temperature u p o n Passage of Water f r o m Atmosphere of 100 Per c e n t Relative Humidity t o One of Zero Relative Humidity across an Area of 1.267 Sq. C m . , through Free Space a n d through Leather Temperature MG. WATER PASSED PER 24 HRS.THROUGH: Ratio O c. Leather Free space Per cent 71 5 98 72 192 20 286 67 236 360 25 66 328 505 30 65 430 660 35 65 560 863 40 66 765 1214 45 63 Average 66
Two factors are worthy of special note. The first is the large amount of water passed by the leather as compared with that passing through free space; the leather in service actually exhibited water repelling properties in shedding rain. The second is the practical constancy of the ratio of the amount of water passed by the leather to that passed through free space oyer the entire range of temperature, as shown in Table I. Over the range 20" to 40" C. there is a deviation of only one unit from 66 per cent, which is quite JTithin the limits of experimental error. Effect of Relative Humidity
The next variable factor studied was that of relative humidity of the atmosphere inside the bottles. Six solutions were made up containing the following concentrations of sulfuric acid in mols per liter: 18.7, 8.8, 6.8, 5.1, 3.3,O.O. These, when placed in the bottles, tend to give atmosphere of 0, 20, 40, 60, 80, and 100 per cent relative humidity, respectively.
Figure &Apparatus to Measure Porosity of Leather A-Outlet to vacuum pump and chamber B-Brass receptacle for holding leather, with hole 1.27 cm. diam. and outer well 3 cm. diam. C-Leather disk 3 cm. diam. D-Brass plug with screw to fit into B and with hole 1.27 cm. diam. E-Calibrated bottle containing water to measure rate of passage of air through leather disk
slot of the brass receptacle, B. D was then screwed tightly into B so that no air could pass through the system without passing through the leather. The vacuum pump was then run so as to maintain a constant reading of 63.5 em. (25 inches) on the vacuum gage. The amount of air passing through the leather was measured by the volume of water passing from bottle F to bottle E , which could be read directly from the calibration marks on bottle E. Measurements were recorded
I N D U S T R I A L A N D ENGINEERING CHEMISTRY
572
. 400
- 35B - 300
- 250
80
2 P
15
20
25
,., -
30
m
For comparison: White duck Rubber
150
.I%. roliodion Peimeability Thickness I,er too sq to mer keiativc of leather
pdislieil isit,li wool. The niriorint of (IT?- rnatcrinl iisrd in earh coat.ing was measured by the \wight of the wet coat applied, determined hg noting t,he loss iii weight of thr bott.lp containing the finis11. 111one 11 aqueous solution of casein was used and ilr the other on of rdlodion in a mistitre of alrohol and ether. The T F Y l l l t S are shown in E'ignres 6 atid 7 niid i n Tables V and TI. w l i i d i tlwy ww drinl
'Tshlr V-Effect
~ i i d
~
,,e*osity
Mm.
344
1.01
76 67
a88
1.15
215
1.18 1.20
.a7
41
45
39
28 12
I8 21
0 11
17
0
Per cent 77
lrxfher
of 1:a~einCsed as P Finishing Mafrrial
32
1.27 1.18 1.15 1.18
1.27 1.18
Directional Effects (1
0
5 6
77
ia
i c C' ?X
