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INDUSTRIAL AND ENGINEERING CHEMISTRY
aging and needs only to be ground to the desired fineness for fertilizer purposes. It is practically insoluble in pure water, is weakly alkaline in reaction, has no deleterious effect on fertilizer bags and machinery, and should prevent, to a considerable extent, increase in soil acidity caused by the use of ammonium salts as fertilizers. Although the alkalinity of the material is sufficient to cause some loss of amrnonia from ammonium salts in fertilizer mixtures, it is believed that it will be possible to overcome this disadvantage. 2. The properly prepared material should contain about 30 per cent or more of available phosphoric oxide (PzOs), as compared with about 19 to 20 per cent in the best grades of ordinary superphosphate. 3. Calcined phosphate not only is superior in mechanical condition to ordinary and double superphosphates, but it improves markedly the mechanical condition of fertilizer mixtures in which it is present. 4. As shown by pot tests, the plant-food value of the phosphorus in calcined phosphate is as high as that of the phosphorus in superphosphate and dicalcium phosphate. 5. The properly prepared material is low in fluorine and offers possibilities as a substitute for bone meal in the preparation of mineral feeds for livestock.
209
LITERATURE CITED (1) Anonymous, M a n u f a c t u r e r s Rec., 99, KO. 15, 38-40 (1931). (2) Bartholomew, R. P., and Jacob, K. D., J . Assoc. Oficial A g r . Chem., 16, 598-611 (1933). 13) Behrendt, G., and Wentrup, H., A r c h . Eisenhiittenw., 7, 95-102
(1933). (4) Bredig, M.A., Z . physiol. Chem., 216, 239-43 (1933). (5) Bredig, M. A., Franck, H. H., and Fiildner, H., 2.Elektroehem., 38, 158-64 (1932). (6) Hendricks, S.B., Hill, W. L., Jacob, K. D., and Jefferson, M. E., IND. ENG.CHEM.,23, 1413-18 (1931). (7) Klement, R., and Tromel, G., 2. physiol. Chem., 213, 263-9 (1932). (8) Korber, F., and Tromel, G., A r c h . EisenhUttenw., 7, 7-20 (1933). (9) Reynolds, D. S., Jacob, K. D., Marshall, H. L., and Rader, L. F., Jr., IND. EXG.CHEX.,27, 87 (1935). (10) Reynolds, D. S.,Jacob, K. D., and Rader, L. F., Jr., Ibid., 26, 406-12 (1934). (11) Ross, W. H., Jacob, K. D., and Beeson, K. C., J . Assoc. Oficial Bur. Chem.. 15. 227-66 11932). (12) SchGede, A.,’Schmidt, W:, and Kindt, H., Z. Elektrochem., 38, 633-41 (1932). (13) Tromel, G., M i t t . Kaiser-Wilhelm-Inst. Eisenforsch. Diisseldorf, 14, 25-34 (1932).
RECEIVED October 17, 1934. Presented before the Division of Fertilizer Chemistry a t the 88th Meeting of t h e .imerican Chemical Society, Cleveland, Ohio, September 10 t o 14, 1934.
Silk Weighting MARION CHINNAND ETHELL. PHELPS, University of Minnesota, St. Paul, Minn.
A
PROCESS known as “silk weighting” has been commonly employed in the manufacture of silk fabrics; as a result the weight of the degummed silk is increased and certain properties of the fabric are changed somewhat. The importance and common use of the process has led t o this study of the first step in the procedure. Interest in the mechanism of the first step of the tin weighting process-i. e., the stannic chloride bath and following rinse-was evidenced as early as 1904 when Heerinann (8) offered as a n explanation the suggestion that silk acts as a catalytic agent. Sisley (11) proposed a n “impregnation” theory. Elod and co-workers (4) presumed that t h e process is a combination of two steps, with stannic acid as a n end product, and that the particles of the latter, because of kheir size, are deposited on the interior of the fiber and cannot diffuse into the solution. Herzog and Gone11 (9) substantiated this explanation in their x-ray experiments; their final conclusion was that the microcrystalline structure is due to the embedded stannic acid. Coughlin (2) showed, by the results of his investigation, that the process is a n adsorption phenomenon. Cook ( I ) , in discussing Coughlin’s work, suggested that the charges carried by the stannic ion, which are greater than those carried by the chloride ion, might explain this phenomenon. EXPERIMENTAL PROCEDURE MATERIAL. The amount of sericin present I-In the raw white Japan silk used in this investigation was found to be 17.48 * 0.01 per cent, as determined b y the usual commercial procedure for degumming silk fiber. The ash content of the silk in question was found to be 0.37 * 0.03 per cent. This value was used as the blank in the gravimetric determinations of weighted silk. WEIQHTINGMETHOD. Only the first step in the weighting procedure was studied:
A series of solutions of increasing concentrations was used to investigate the manner in which tin from the “pinking” bath is retained by the silk. Solutions of stannic chloride in five concentrations-i. e., specific gravity 1.0775. 1.1449, 1.2154, 1.2750, and 1,3498-were used for “pinking.” Weighed samples of silk (approximately 6 grams) were immersed in 150 cc. of each solution in triplicate for one hour a t a temperature ranging from 10” to 15’ C. Each sample was extracted on a Biichner funnel, and then one liter of cold distilled water was allowed to run through the same funnel; as a result, hydrolysis was assumed to be complete, After the sample had been air-dried, it was placed in a vacuum oven and dried to constant weight at a temperature of 100” * 2” C. under high vacuum.
SAMPLE. The increase in weight of each sample after the stannic chloride bath and hydrolysis was measured by the difference in weight between the original dry weight of the sample and the dry weight after treatment. The percentage of weighting was calculated on the original dry weight. The amount of tin removed from the bath by the sample was calculated from the stannic oxide obtained by ashing a portion of the weighted sample, and the percentage of stannic oxide was calculated on the dry weight after treatment. SOLUTION. The amount of tin removed from the solution was determined by measuring the stannic oxide present in the original and in the equilibrium solutions, assuming a n y difference between the two amounts to have been removed by the silk: To 10-cc. aliquots of stannic chloride solution was added drop by drop concentrated ammonium hydroxide diluted one to one with water until a faint precipitate appeared to be permanent. T o this were added 10 cc. of a saturated solution of ammonium nitrate and 100 cc. of boiling water to hydrolyze the stannic chloride. The precipitate was allowed t o settle while remaining on a steam bath for 30 minutes. The supernatant liquor was decanted and the precipitate washed five times with a one cent hot ammonium nitrate solution. A sixth washing of water only was used to aid in removing the precipitate in its entirety t o the filter paper. The precipitate was further washed until the filtrate gave a negative test for chlorides with silver nitrate. Filter paper and precipitate were dried and ashed.
!Et’
210 INDUSTRIAL AKD ENGINEERING CHEMISTRY Vol. 27, No. 2 One drop of nitric acid was added, and ignition was repeated samples, is shown graphically as the broken line in Figure 2. slowly to avoid spattering. The ash was dried in a muffle furnace at 500' C. for successive periods of 10 and 6 hours. The maximum amount of stannic oxide is found in those Six-hour periods of heating were repeated until two successive samples that were weighted in a solution of stannic chloride weighings gave a constant weight (IO, 12). with a specific gravity of 1.2750. The next higher concentration of the weighting salt shows a lower deposit of stannic I n addition to the analysis for stannic oxide on the silk, the weighted samples were exposed to a standard atmospheric oxide on the silk. This critical concentration of the stannic chloride solutions used condition-relative humidity of 65 * 1 per cent, and temI I in this studv--1.2750 m 1 perature of 70" * 2" F. (21.1" * 1.1" C.) until each reached specific gravity-is BO I /.\ a constant weight as determined by consecutive weighings. shown both by the per1 1 A . \ The percentage of moisture regain was calculated on the dry centage increase in weight of samples after treatment. weight and the percentage of stannic oxide in RESULTSOF WEIGHTING SILK the sample. Assuming The results of weighting 6-gram samples of degummed that the stannic oxide silk in several concentrations of stannic chloride show that -.. represented the weightan optimum concentration for maximum retention of weight/05 //o //s /pO /25 /30 /35 ing in the silk, Figure ing on the silk is reached by a solution of 1.2750 specific Concn 5 n C 4 so/u?mnr /o8 ,pr 2 w a s d r a w n to show gravity. The gain in per cent in ascending order of conFIGURE2 . R E L A T I O N S HBI P Ethe relationshb between centration of stannic chloride is summarized as follows : TWEEN PERCENTAGE GAIN IN the actual percentage of WEIGHT OF SAMPLE,BASEDON weighting in the Av. GAININ Av. G A I NIN WEIQHT O F WEIGHTO F DRYWEIGHTOF WEIGHTED SnCIr SOLN. SAMPLEE SnCL SOLN. SAXPLES PLE, AND PERCEXTAGE ST.4NNIC and the stannic O x i d e S p . or. % s p . or. % shown therein. Although OXIDE FOUNDIN SAMPLE 1.0775 2.03 1.2750 10.67 the optimum concentra1.1449 6.06 3.17 1.3498 1,2154 8.99 1.3499 2.00 tion of the stannic chloride bath was found to be the same for For the highest concentration used (a solution of 1.3498 both series, the curve showing percentage of weighting rises specific gravity) the amount of weighting retained by the to a higher point a t this concentration than does the curve silk dropped to nearly the same gain as was observed with for percentage stannic oxide. It is apparent here that the a solution of 1.0775 specific gravity, which was the lowest stannic oxide found does not account for the total amount concentration used in this study. In order to check this of weighting. If the gain in weight might be accounted for sudden change in an otherwise steady gain in the weight as tin alone, the two curves should coincide. It is thought of the silk which was in direct relationship to the increasing that water may have been adsorbed by the silk together c o n c e n t r a t i o n s of with the tin salt and may have been weighed as weighting. stannic chloride in the weighting b a t h s , a n STANNIC OXIDEPRESENT IN SOLUTIONS other sample in tripliI n consideration of the fact that each sample showed a cate was immersed in a stannic chloride solu- gain in weight after immersion, the amount of stannic tion of the same high chloride remaining in the equilibrium solution would prec o n c e n t r a t i o n . The sumably be less than in the original solution. Table I same low retention was gives the amount of stannic chloride in original and equievidenced again, which librium solutions per gram of sample, and the difference confirmed the results between the two, or the amount removed per gram of sample. o b t a i n e d in the first In considering these values, it may be noted that, for the bath of 1.3498 specific samples immersed in the stannic chloride bath of the lowest, gravity. The optimum concentration, there has been a removal of stannic chloride FIGURE1. RELATIONSHIP BEconcentration of these from the bath by each sample in direct proportion to iris TWEEN ORIGINAL CONCENTRATIONSstannic chloride solu- respective gain in weight. However, the equilibrium soluOF STANNIC CHLORIDE WEIGHTING tions for weighting silk tions in certain cases show a greater content of stannic BATHS, AND PERCENTAGE INis also shown graphi- chloride than the original solutions. This is especially true CREASE I N WEIGHTOF SILK in the case of the samples weighted in solutions having cally in Figure 1. Heermann (7) found in weighting de-gummed organdne specific gravities of 1.2750 and 1.3498. Previously, in corn-, that the amount of tin removed by the silk from the stannic paring the increase in weight and the amount of stannic chloride bath was greatest with a solution of 35' BB., or oxide found in each sample, the values for each were shown approximately a specific gravity of 1.32. Elod (3) verified to be greatest for samples weighted in a bath of 1.2750 Heermann's work, Considering these findings, the optimum specific gravity. Although the three samples weighted in concentration of the "pinking" bath observed in this study the bath of this particular specific gravity showed a maxiapproaches Heermann's critical point of maximum adsorp- mum retention of stannic oxide and a maximum increase in tion. The decided drop, evidenced in bhis investigation, in weight, two did not, as is shown in Table I, remove stannic the amount of weighting retained by the silk fiber between chloride and water in the same proportion as those comthe specific gravities of 1.2750 and 1.3498 may be due t o a pounds were present in the original solution; analyses of the change in the silk itself. Harris and Johnson (6) state that equilibrium solution for the third sample immersed in this silk is readily soluble in concentrated solutions of salts, acids, concentration showed only a slight loss of tin from the and bases, and that this reaction is accompanied by hy- solution. As previously implied in the discussion of the data graphidrolysis. cally presented in Figure 2, it might be said that these samples STANNICOXIDEPRESENT IN SAMPLES showed a preferential adsorption of water, for, although they The amount of weighting present in the silk, determined removed some tin, enough water was removed in addition to by the stannic oxide found on ashing aliquot portions of the offset all or nearly all evidence of loss of tin in the analyses of
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February, 1935
INDUSTRIAL AND ENGINEERING CHEMISTRY
the equilibrium solutions. The fact that samples weighted in the solution having a specific gravity of 1.3498 may have still more markedly preferred water to tin apparently would explain the reason for the low stannic oxide content found. Moreover, it has bee,n shown previously that the amount of weighting retained from a bath of this high concentration was equivalent to that retained from the lowest concentration. However, alt,hough the amount of weighting retained was comparable for the two baths, the equilibrium solution for the higher concentration showed no loss of st:tnnic chloride on analysis, while such a loss was observed for those of the lower concentration.
211
should take place a t that point where the positive and negative adsorption isotherms converge. Figure 3 shows that this point corresponds to log concentration of +0.13 or an equilibrium concentration of approximately 1.35 moles of stannic chloride per liter. The silk samples containing varying amounts of weighting under constantly controlled atmospheric conditions showed a difference between the original dry weight and their constant weight of approximately 8.61 per cent. As evidenced by this fact, the amount of atmospheric moisture adsorbed by silk fabrics is independent of the amount of weighting present. COKCLUSIONS
TABLEI. STANNIC CHLORIDE REMOVED FROM SOLUTION AND GAIN IN WEIGHT SnClr IN SnC14 IN ORIGINALEQUILIBRIUMSnCL GAININ SOLN.PER S O L N PER . REMOVED WEIQHTPER SP. GR. SAMPLESAMPLE G R A MOF G R A MO F PER G R A M GRAMOF OF SOLN. No. WEIOHT SAMPLE SAMPLE O F SAMPLE SAMPLE 1.0775 1.1449 1.2154 1.2750 1.3498
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15
Gram
Grams
Grams
Gram
Gram
4.7148 4.7217 6.0400 5.7350 5.1973 5.5090 5.5701 4.7604 4.9042 4.8027 4.7411 4.6066 4.7850 5.6392 7.1878
3.2292 3.2245 2.5207 5.4037 5.9627 5.6353 8.0223 9.3868 9.1116 11.4186 11.5069 11.9047 15.0972 12,8103 10.0504
3.1680 3.1689 2,4601 5.5119 5.5283 5.6450 8.0867 8.9937 8.7828 11.9003 11.8471 11.8327 15.3531 13.5379 10.6455
0.0612 0,0556 0.0606
0.0215 0.0191 0.0‘202 0.0595 0.0616 0.0607 0.0889 0.0908 0.0837 0.1062 0.106‘2 0.1046 0.0120 0.0299 0,0335
”
0.4:344 0.0803 ’%
0.3931 0,3288
’
’
0.0720 1
‘1
”
a Concentration of equilibrium solution greater t h a n that, of original solution.
MECHANISM OF WEIGHTING Using Freundlich’s formula (5) for an adsorption phenomenon, log X / m
=
log a
+ b log C
where X
= weight of substance adsorbed, grams m = weight of‘ adsorbent, grams C = concn. of soln. at equilibrium a, b = constants depending on the nature of
and the substance adsorbed
the adsorbent
1. Of the series of stannic chloride solutions used in this study, the optimum concentration for weighting was found to be 1.2750 specific gravity, with a 10.57 per cent maximum retention of weighting on the silk. 2. The amount of weighting retained by the silk, as determined by the stannic oxide found on ashing, reached a maximum with a stannic chloride solution of 1.2750 specific gravity, in which case the stannic oxide found in the silk amounted to 8.35 per cent. 3. The retention of weighting by the silk from stannic chloride solutions of lower concentrations is a positive adsorption reaction. 4. The retention of weighting by the silk from stannic chloride solutions of higher concentrations is a negative adsorption reaction. 5. The amount of weighting retained by the silk, measured both by total weighting and stannic oxide, is approximately the same for the lowest and the highest concentration of stannic chloride solutions used. 6. The difference in the values for total amount of weighting retained by the samples, and stannic oxide found in the samples, is assumed to be due to the effect of a new equilibrium reached in the rinsing bath in combination with positive and negative adsorption. 7. Weighted silk adsorbs approximately 8.6 per cent of moisture under standard conditions of temperature and humidity, regardless of the amount of weighting present in each case.
ACKNOWLEDGMENT
h
LOU
grams per gram of sample. This graphic illustration shows that the reaction apparently shifts from positive to negative adsorption. the values for 2 the first three concentrations showing positive . . adsorption, CorBc e n f r d f i on and the values for
a d s o r p t i o n . -41though the value for the fourth concentration represents maximum retention of weighting on the fiber, it falls in the region of negative adsorption. From the data available in this study i t cannot be stated a t what precise point the change from positive to negative adsorption occurs. It MATERIAL ADSORBIZD
SAMPLE
PER
GRAMOF
The authors express their gratitude for the helpful criticism and suggestions of R. A. Gortner and W. M. Sandstrom during the course of this investigation, and their appreciation to E. M. Shelton, formerly of the Cheney Brothers Research Laboratories, from whom the raw silk was obtained. LITERATURE CITED Cook, A. A., Am. Salk J., 51, 43-4 (1932). Coughlin, W. E., J. Phys. Chem., 35, 2434-45 (1931). Elod, E., Kolloidchem. Beihefte, 19, 296-362 (1924). Elod, E., Teichmann, L., and Pieper, E., Z. angew. Chem., 40, 262-4 (1927). Gortner, R. A., “Outlines of Biochemistry,” 1st ed., pp. 166-87, New York, John Wiley & Sons, 1929. Harris, M., and Johnson, T . B., IND.ENG. CHEM.,22, 965-7 (1930). Heermann, P., Farber-Ztg., 14, 335-9 (1903). Ibid., 15, 165-70, 197-200, 214-19 (1904). Herzog, R. A., and Gonell, H. W., 2. angew. Chem., 39, 380-1 (1926). Scott, W. M., “Standard Methods of Chemical Analysis,” 2nd ed., pp. 422-3. Xew York, D. Van Xostrand Co., 1917. Sisley, P., Chem.-Ztg., 35, 621-2 (1911). Treadwell, F. P., and Hall, UT.T., “Analytical Chemistry,” 3rd ed., Vol. 11, p. 321, New York, John Wiley & Sons, 1911. R E C ~ I V EJuly D 7, 1934. Publiahed with the approval of the director as Paper No. 1283, Journal Series, Minnesota Agricultural Experiment Station.
