December, 1942
INDUSTRIAL AND ENGINEERING CHEMISTRY
1495
those prepared from data obtained by using the electrical device. The point of significance here is that there are usually abrupt volume changes during the pasting of a starch which could yield information of value in differentiating between starches.
Summary A modified rotating-cylinder viscometer suitable for the viscosity measurements of starch pastes has been described. It is believed that this instrument has the following advantages : 1. Continuous, uninterrupted measurements of viscosity may be made over a wide range of temperatures or at a given temperature for an indefinite period of time. 2. It provides for the measurement of viscosity in absolute units. This removes the need of setting up arbitrary standards and places viscosity studies of starches on a sounder theoretical basis. . 3 . The viscosity ran e is broad. As long as the liquid does not channel, viscosities o? one poise and more are easily measured. 4. No evidence of turbulent flow has been observed. OF VISCOSITYINTO POISES FIGURE 4. GONVERSION
time during the cooking period). For comparison, the volumes of the Irish potato suspension and the standard oil were taken as identical a t 30’ C. and from that point 1 values of the oil were calculated from specific volumes, It is apparent from the plots that changes in density in Irish and sweet potato starch pastes respond to the same causative factors that effect viscosity changes. The two particular starch samples shown here follow each other as closely as any that have been tested and, therefore, give an idea of the minimum deviations to be expected between starches from different sources. Among the other half dozenstarches tested in this way, some show pronounced differences. There is no intention to imply that the method employed for making I measurements is accurate in the sense that the impressed alternating current is without influence upon the behavior of the suspension or paste. Actually the current acts through electrolysis or polarization to accentuate the volume changes and to cause a slight shift in the viscosity curves. Although I measurements which are made manually on starch pastes are less precise for a number of reasons, the curves prepared from them have the same general form as
Experiments with the instrument indicate that 60 r. p. m. is the lowest permissible angular rotation and 10 per cent is the most satisfactory concentration for starches in general. Viscosity measurements may be reproduced with considerable accuracy. Viscosity curves throughout a complete cycle of temperature changes are given. These curves show characteristic differences between starches and should be of value in their characterization. The plotting of experimentally determined I values, which reflect changes in density, against the temperature differentiates sharply between starches and should contribute also to their characterization.
Literature Cited (1) Blinc, M., and Samec, M. M., Congr. intern. tech. chim. ind. agr., Compt. rend. Vd Congr., 2, 214-49 (1937).
(2) Caesar, G.V., IND.ENG.CHEM.,24, 1432-5 (1932). ( 8 ) Caesar, G.V., and Moore, E. E., Ibid., 27, 1447-51 (1935). (4) Radley, J. A., “Starch and Its Derivatives”, New York, D. Van Nostrand Co., 1940. PREBINTED in part before the Division of Agricultural and Food Chemistry at the 102nd Meeting of the AMERICAN CHEMICAL SOCIETY, Atlantio City, N. J. Contribution 267, Department of Chemistry, Kansas State College.
Condensation of Vapors from Noncondensing Gases-Correction It has come to the author’s attention that a consistent error exists in the calculation of the required surface area in the above article, which appeared on pages 1248-52 of the October issue. The mass velocity, 0,for point 2 (page 1250, column 1) was calculated as follows: G = 20,000
- (24.2 X 88 X 0.4333) = 19,079
It should read: G
DEPTHOF FIGURE5. VARIATIONSIN EFFECTIVE WITH TEMPERATURE
5
20,000
- [(24.2 X 88)/0.4335]
15,080
This error introduces errors in the calculated values of Re, h,, and K,and considerably increases the surface area required. It does not, however, altersthe relative results of the two solutions and in no way invalidates the proposed modification in the method of design. On page 1249, column 1, under NUMBER OF TUBES the value SOLUTIONS of 8760 for the rate .of flow should read 8670. JULIAN C. SXITH
