August,, 1924
I N D LT8TRIAL A N D ENGINEERING CHEMISTRY
813
Surface Tension of Sugar Factory Products‘ By
I(. R. Lindfors
MICHIGANSUGAR Co., SAGINAW,MICH.
The surface tension of a NASMUCH as a small Colloidal substances are of great importance in sugarhouse work dilute solution of egg white amount of gums or as they influence boiling, crystallization, and the color of the sugar is 28 per cent and of gelatin colloids will greatly into a considerable extent. Since they have a strong depressing in12 per cent less than that of crease the viscosity of fillfluence upon the surface tension, the determination of the latter water. mass and sirups, cause diffifurnishes a means of the estimation of the colloids present. W i t h The surface tension of a culties in boiling, interfere d u Nouy’s apparatus, the surface tension can be found in harf a 25 per cent solution of a with the crystallization of minute. Mineral salts have very little effect upon the surface tenmolasses containing a large the raw pans, and thus desion; hence it bears no relation to the purity of thejuices. On the amount of gelatinous gums crease the extraction, it is other hand, colloidal silica, gums, and organic acids depress the was 42.1 dynes. After filevident that a practical surface tension to quite a n extent, even in very dilute solutions. tration it rose to 47.6 dynes study and control of the Therefore, surface tension immediately shows any irregularities -an increase of 5.5 dynes. colloids and the means of in the sugarhouse work, especially improper carbonation, insufiSteffen’s c oncen t r a t etheir removal may lead to cient heating, poor infiltration, and inferior quality of the sugar. that is, Steffen’s waste information of great value Adsorption of colloids to the surface of sugar particles interferes water from the hot sacchato the sugar industry. with the rapid growth of the crystals. Inasmuch as the adsorption is rate presses, carbonated, That such a study has practically inversely proportional to the surface tension, the latter gives filtered, and evaporatednot yet been undertaken to direct information as to the presence of such interfering substances, of 54” Brix, representing a any extent is undoubtedly and, by proper control of the beet end, allows the elimination of a solution of practically nondue to the slow and cumberlarge part of the disturbing colloids. Surface tension further indisugars only, has a surface some methods of the decates the keeping quality of granulated sugar; the adsorbing power of tension of 51.7 dyn8s; ditermination of gums and charcoal and carbons; the comparative refining values of similar luted with an equal amount allied substances. Evaporaw sugars; and, finally, differentiates between beet, refinery, and of water, 56.6 dynes. ration, crystallization, visplantation white granulated sugar. Much work and research still The following is the only cosity of the mother liquor, remains to be done before this field is completely covered and it is table found of the surface adsorption of impurities on hoped that this will be undertaken in the near future. tension of cane sugar the sugar crystals are all p h y s i c a l operations or Sugar Temperature Surface Tension phenomena; hence physical examination of the products inPer cent c. Dynes volved ought to furnish some practical information not ob16.9 78.02 0.0 19.17 63.59 5.3 tainable by chemical analysis. The viscometer has already 18.82 57.01 10.0 19.58 50.83 24.8 been applied to some extent to the study of sirups and fill19.44 59.17 29.85 mass, especially as related to the final boiling, but when it These values were found by the capillary tube method, comes to a control of the cause of the variations in viscosity, or an investigation of the physical characters of diffusion and which gives considerably lower results than the static, especially with colloids. As the instrument designed by thin juice?, this instrument is of comparatively little aid. du Nouy is based on the static method, all figures given in SURFACE TENSION this paper are determined by this method, unless quoted The surface tension of mineral salts in solution is prac- from other sources. tically the same as that of water. Gums or emulsoids have The surface tension of cane sugar thus found is as follows a strong depressing effect; hence it would appear that the (all determinations were made a t a temperature of 20” C.): surface tension, within certain limits, is proportional to the Sugar Surface Tension amount of such substances present. The practical operaPer cent Dynes 0 77 tion offers no difficulties; by using du Souy’s apparatus the 73 5 surface tension can be determined in half a minute. 75 S 10 The following may be taken as typical examples of the 7!,.. 20 40 78 surface tension of inorganic salts, concentration 1.5 mols 55 79 per liter:2 Dynes No scientific accuracy is claimed for this table. The re76.9 Potassium nitrate sults were obtained by routine methods, working with ordi77.6 Potassium chloride 79.9 Potassium carbonate nary lump sugar. 77.2 Sodium nitrate 77.8 Sodium chloride FACTORY CONTROL 72.2 Ammonia The value of surface tension in relation to the control of Compare with the foregoing figures the strong depressing sugar factmy operations is probably best illustrated by a action of some organic substances: few incidents and observations from the past campaign. Dvnes On testing the surface tension of the first carbonation 57.5 Acetic acid (10.6 per cent) juice it was found that the same suddenly jumped from 62.1 Gum arabic (0.5 per cent) 33.1 Butyric acid (1 mol per liter) 60.0 to 63.5 dynes. 1nquiry.brought out the fact that a Sodium oleate .(0.002 N ) 28.5 breakdown in the Steffen plant had made it necessary to use 1 Presented before the Division of Sugar Chemistry a t the 67th Meeting milk of lime in place of saccharate; hence the increase. It of the American Chemical Society, Washington, D. C., April 21 t o 26, 1924. 2
Taylor, “The Chemistry of Colloids,” p. 241.
8
Grunmach, A n n . p h y s . , 3, 660 (1900).
INDUSTRIAL A N D ENGINEERING CHEiVISTRY
814
may be of interest to note that the purity actually dropped from 87.2 to 86.7 per cent. Another time it was observed that the surface tension of the second carbonation juice had dropped to 55.2 dynes. Ordinarily it is about the same as, or slightly higher than that of the first carbonation, so an investigation was made to find the cause of the difference. The purities furnished no answer, being 87.2 and 90.6 per cent, respectively, the increase being due principally to the solution of raw sugar from the melter, which was pumped into the second carbonation tanks. The juice from the melter was therefore tested and found to have a surface tension of 51.7 dynes, and a purity of 94.0 per cent. This being rather low, the amount of wash water used a t the brown sugar centrifugals was increased, with satisfactory results. It is therefore evident that no direct relation exists between surface tension and purity. But nothing else could be expected, since purity principally indicates the amount of mineral impurities present, while the surface tension depends upon the organic matter and colloids in the juices. In order to determine the efficiency of filtration in removing substances of low surface tension, thick juice was tested before and after filtration. Surface Tension, Dynes Before filtration After filtration Increase
52.4 54.5
57.3
2.1
1 0
55.2
51.1
58.3 _ _ _ _ -56.6 - _ 54.5 _ 1.4
3.4
The first three samples were filtered through ordinary filter cfoth, the last one through paper pulp. It is evident that filter cloth alone is of little value in this connection, and that the addition of some filtering aid is required for effective filtration. The high surface tension of diffusion juice is puzzling. One would naturally expect it to be very low, as diffusion juice contains large amounts of gums and other impurities of organic nature, which are removed by carbonation. Hence there ought to be an increase in the surface tension after carbonation. Just the opposite happens, however. The surface tension of diffusion juice varies from 64 to 71 dynes, increasing with purity and dilution, whil
