Effect of Temperature on Determination of Water-Soluble Matter in Leather HENRYB. MERRILLAND CLIFFORD BENRUD,A . F. Gallun
I
N DETERMINING water-soluble matter in vegetabletanned leather by Wilson's method (@,a weighed sample of leather is first freed from fat by extraction with chloroform, and then extracted with running distilled water in a Wilson-Kern extractor until the percolate no longer gives a positive test for non-tannin with ferric chloride. For calf upper leather, with a water flow of approximately 500 cc. per hour, this point is generally reached in 4 days. When the percolate no longer gives a positive test with ferric chloride, the leather is removed quantitatively from the extractor, dried first a t 50" C. and then at 102" C., and weighed. The difference between 100 per cent and the sum of the percentages of water and fat (in the original leather) and water-insoluble residue is taken as percentage of water-soluble matter. I n the author's laboratory, the determination is carried out a t room temperature. The question arises as to how great is the effect of seasonal differences in laboratory temperature upon the rate of extraction of water-soluble matter from the leather. To settle this point, samples of hide powder I
I
10 DMS
eo
1
50
extraotsd
FIGURE1. RATE OF EXTRACTION OF WATER-SOLUBLE MATTERFROM OAKBARK-TANNED HIDEPOWDER AT DIFFERENT TEMPERATURES
tanned with oak-bark extract were extracted at temperatures of lo", 20°, 30", and 40" C. for periods of from 1 to 32 days. Results show that increasing the temperature from 20" to 40" C. has very little effect upon the rate of extraction of water-soluble matter from leather, and that a change from 20" to 30" (the usual laboratory range) produces an effect which is less than the difference frequently found between duplicate determinations run side by side. A change in temperature from 20" to 10" C., however, markedly retards the extraction of water-soluble matter. It is concluded that control of temperature is unnecessary in determining watersoluble matter by Wilson's method, except that the temperature of the room must not be less than 20" C. If this condition cannot be fulfilled, the distilled water used should be preheated to 25" C., say by passing it through a block tin coil in a bath maintained at 25 " * 1" C.
4 Sons Corp., Milwaukee, Wis.
Chemists' Association method). After 24 hours the powder was filtered on a muslin cloth, wrung out by hand, and placed in a fresh 2000-cc. portion of liquor. This process was repeated five times. Finally the tanned powder was freed from adhering tan liquor by alternately suspending it in distilled water and wringing out, until the washings were practically colorless. The powder was then air-dried, and analyzed for water, ash, and hide substance. Tannin plus watersoluble matter was obtained by difference, PROCEDURE Fifty grams of air-dry tanned hide powder were placed in each of four modified Wilson-Kern extractors (1) which were immersed to the necks in thermostats a t lo", 20°, 30°, and 40" C., respectively. The ground-glass joints were protected against possible leakage by a section of tightly fitting Gooch filter tubing. The outlet of each extractor was attached to a capillary tube bent into an inverted U, which served to carry the percolate over the thermostat wall. The inlet of each extractor was attached to a reservoir of distilled water. The distilled water level inside the extractors was such as to submerge completely the charge at all times. The rate of flow of the distilled water was adjusted to 500 cc. per hour. At the end of 1 , 2 , 4 , 8 , 1 6 ,and 32 days, each extractor was removed from its thermostat, and an amount of wet hide powder was withdrawn equivalent to about 7 grams in the air-dry state. Each portion withdrawn was composed of equal weights taken from the top and from the bottom of the hide-powder column in the extractor. Each portion was air-dried, and analyzed for water, ash, and hide substance. Apparent percentage of tannin was obtained by difference for each temperature and period of washing. The percentage of water-soluble matter-i. e., per cent of the original tanned powder that had dissolved-was calculated by finding the number of grams of vegetable matter, after washing, which was combined with a number of grams of hide substance equal to the per cent of hide substance in the original leather, and subtracting this number from the percentage of tannin plus water-soluble matter in the original leather. All percentages were corrected to the water-free basis. RESULTS The percentage of water-soluble matter found in this manner for extraction periods of 1 to 32 days, at temperatures of 10" to 40" C., are given in Table I and in Figure 1. The rate of extraction, as shown in Figure 1, increases markedly from 10" to 20" C., but is little affected by further increase in temperature, For a 4-day extraction period, the percentage of water-soluble matter found increases 0.43 per cent per degree rise in temperature between 10" and 20" C.,but only 0.09 per cent per degree between 20" and 30" C., and only 0.07 per cent per degree between 30" and 40" C. Thus an increase in temperature from 20" to 30" would increase by only 0.9 per cent the percentage of water-soluble matter found by a 4-day extraction a t room temperature. Agreement of duplicate determinations to within 1 per cent is considered passable in this laboratory, so that we may conclude that only in the most extreme hot weather will high room temperatures materially affect the analytical results. On the other hand, it is very evident that, if the temperature is al-
MATERIALS Two hundred grams of purified hide powder (3) weresuspended in 2000 cc. of a solution containing 80 grams of liquid oak-bark extract (1 per cent tannin by the American Leather 66
INDUSTRIAL AND ENGINEERING CHEMISTRY
January 15,1932
67
lowed to fall even a few degrees below 20' C. and the time of extraction is kept a t 4 days, the results obtained will be abnormally low. When a minimum room temperature of 20° C. cannot be maintained day and night during the extraction of water-soluble matter, it appears advisable to bring the inflowing water to 25" C., which can be done very simply by passing it through a block tin coil in a bath maintained a t the desired temperature within a range of *lo.
straight lines whose slopes increase with increasing temperature. It appears reasonable to suppose that the slope of the rectilinear portion of each curve represents the rate of hydrolysis of the hide-tannin compound a t the temperature in question. If this be true, then by extrapolating to zero time the rectilinear portion of each curve, a value would be obtained which would represent the percentage of water-soluble matter in the leather corrected for dissolved tannin. When this is done, for the four curves of Figure 1 the corrected values for TABLEI. EFFECT OF TEMPERATURE UPON RATE OF EXTRACTION OF WATER~OLUBLE MATTERFROM OAK-BARK-TANNED HIDE water-soluble matter show an extreme variation of less than 0.5 per cent, indicating that the distinction between fixed POWDER tannin and water-soluble matter is not affected by change in INCREASE PER DEQREE DAYS APPARENT WATER-SOLUBLE IN TEMPERATURE temperature of extraction over the range studied. WA0EED MATTBR FOUNDAT: INTERVAL AT: 10' C. 20' C. 30" C. 40' C. 10-20° C. 20-30' C. 30-40' C.
1 2 4 8 16 32
%
%
16.8 19.8 22.7 27.1 30.0 31.4
18.9 23.0 27.0 29.6 30.9 33.6
% 20.8 (22.6) 27.9 30.4 32.0 35.1
% 21.8 24.5 28.6 30.6 32.7 37.0
%
0.21 0.32 0.43 0.26 0.09 0.22
%
0.19 (-0.04) 0.09 0.08 0.11 0.15
LITERATURE CITED
%
0.10 0.19 0.07 0.02 0.07 0.19
The shape of the several extraction curves is interesting in that these curves do not converge, but rather tend to become
(1) Merrill, H. B., J. Am. Leather Chem. Assom., 24, 244 (1929). (2) Wilson, J. A., Ibid., 16, 264 (1921). (3) Wilson, J. A., and Merrill, H. B., Ibid., 21, 2-30 (1926). RECEIVED July 8, 1931. Presented before the Division of Leather and Gelatin Chemistry a t the 80th Meeting of the American Chemical Society, Cincinnati, Ohio, September 8 to 12,1930.
Binary System Carbon Tetrachloride-Ethylene Dichloride Their Boiling Points and Specific Gravities as Aids in Analysis H. D.YOUNGAND 0. A, NELSON, Bureau of Chemistry and Soils, Washington, D. C.
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INCE carbon tetrachloride-ethylene dichloride mixtures have been used as fumigants against moths and other insects ( I ) , it has become increasingly important to find a rapid and reliable method of ascertaining the ratio of the two components in such a mixture. Carbon tetrachloride contains 92.20 per cent chlorine and ethylene dichloride 70.65 per cent, the difference being 21 -55 per cent.. To detect a difference of 1 mole per cent in the composition of a mixture of these compounds by a determination of the chlorine content would therefore require that this constituent be known to the nearest 0.2 per cent. Such a degree of accuracy might possibly be attainable by the best methods now in use, but only by taking extreme precautions with-consequent loss of time.
ANALYSISBY PHYSICAL METHODS Three physical constants-refractive index, specific gravity, and boiling point-were considered as offering bases upon which to found a method of analysis. Rosanoff and Easley (.2) found the refractive indices of carbon tetrachloride and ethylene dichloride at 25.2' C. to be 1.45730 and 1.44218, respectively. As these figures are so close together that extreme care under very closely controlled conditions would be necessary to get any results a t all, nothing further was done with this factor. The specific gravities determined on purified samples prepared by prolonged drying of chemically pure reagent materials over calcium chloride followed by distillation, were found to be 1.591 for carbon tetrachloride and 1.252 for ethylene dichloride, both at 20" C. This is a more favorable difference, and the whole composition-specific gravity relationship was therefore determined.
The pure compounds were mixed in the following ratios (mole per cent): 100% CCL; 90% CC14 and 10% CzH4C12; 80% CCL and 20% CZH,Clz;. . . 0% ccI4 and 100% CZH4Cl2. The observed specific gravities of these mixtures are given in Table I and shown graphically in Figure 1. As would be expected, the specific gravity-composition curve shows no irregularities, so a determination of this constant alone might be used to ascertain the composition. The total range of specific gravity is about 0.340, equivalent to approximately 0.0034 per 1 mole per cent change in the concentration of one of the constituents. Therefore, specific-gravity determinations can be made to yield analyses with an accuracy of * 1mole per cent, always with the assumption, of course, that the mixture contains no impurity. GRAVITIES AND BOILINQ POINTS OF TABLEI. SPECIFIC CARBONTETRACHLORIDE, ETHYLENE DICHLORIDE, AND MIXTURES OF THE TWO COMPOSITION IN MOLES CClr CnHdCla
%
%
100 90 80 70 60 60 40 30 20 10 0
0 10 20 30 40 50 60 70 80 90 100
SPECIFIC GRAVITYBOILINQ POINT AT 20"/20° AT 760 MM. O
1.691 1.563 1.531 1.600 1.469 1.435 1.402 1.367 1.330 1.292 1.262
c.
76.52 76.82 75.42 75.30 75.39 75.74 76.39 77.26 78.49 80.23 82.85
The difference in boiling points between ethylene dichloride and carbon tetrachloride is 6.33' C. As boiling-point differences can be determined to about *0.002' (the limit of accuracy of a Beckman thermometer), it is evident that very
