706
T H E JOURNAL OF INDUXTRIAL A N D ENGINEERING CHEMISTRY
20
40
60
80
100
’
I20
140
160 I80 200
240
220
260 2x0
Pressure, qmms per square renitmeter
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FIG.3
The dimensions of the capillaries are given in Table 111. TABLE 111-DIMENSIONS Diameter Minor Length Axis Cm. Cm. 2.69 0.198 0.107 2.79
Capillary No. 1
2
AND CONSTANTS OF CAPILLARIES Diameter Constant 1 Major Calculated C of Axis Diameter Equation d Cm. Cm. 2 0.214 0.2055 0.01605 13.1 0.110 0.1085 0.00119 25.7
-
The variations in f i n Table I1 may be partly due to error in measurement of capillaries, but it is believed that the main cause is the error in the graphical determination of p . The two capillaries differed too greatly in dimensions, so that suitable graphs could not be obtained by both capillaries for the same sample. Capillary 1 should have been smaller. I n Green’s table the maximum change in value of Pd I!
due to change of capillary is only 14 per cent, which is less than with any sample in Table 11. A slight difference in the location of the graph, owing to a different weighting of the various points, will cause a great variation in p , and hence in f. For this reason it is believed that most of the error in Table I1 is due to the attempt to locate the straight line necessary to find p , when all or nearly all of the points were in reality on the curved part of the graph. An additional source of error is the lack of accurate formulas. EXAMINATION OF RESULTS WITH CAPILLARY When highly soluble dextrins.are compared a t the same concentration, 55 per cent, it is noticed first that tapioca dextrin A has a zero yield shear value and is consequently a viscous liquid. The rigidity or viscosity is 5 . 6 poises. The consistency of corn dextrins is shown in Table IV. TABLE IV-CONSISTENCY Kind
C A D B
OF CORN DEXTRINS, 55 PER Yield Shear Value 200 477 229 524
DRYSOLID Rigidity
CENT
8.1 7.0 6.6 5.7
When the conversion takes place in the dextrinator, highly soluble compounds are first formed, as indicated by C in Table IV. The yield shear value is low and the rigidity high. When converted further, it is known that an insoluble compound begins to appear in A. This is indicated by the higher yield shear value. When still further converted to D, another change takes place, and the yield shear value, as well as the rigidity, decreases. This is well known in the actual use of these three products, from the fact that D gives a paste which has a smooth honey-like consistency. By a simple efflux test it had been considered that C was the thinnest, A medium, and D the thickest. I n the case of B the
Vol. 13, No. 8
high yield shear value and low rigidity distinguish it from other products. If the yield shear value could be reduced, the product would have a consistency approaching that of tapioca dextrin. The subject requires further study. In Table I1 the darker colored tapioca dextrins are viscous, and the lighter ones have a low yield shear value. British gums have a high yield shear value. It is interesting to see that British gum B, with about half the solubility of A, has about the same yield shear value but lower ,rigidity. This can be explained by the longer conversion of B which changes the insoluble part to compounds of less gelatinizing power, that is, lower yield shear value. The difference between 25 per cent thin boiling starch B and British gum C is striking, the yield shear value for the former being 1400, while for the latter it is 792. This explains why B sets while C stays fluid. A comparison of the 8.3 per cent starches is interesting. An addition of 0.25 per cent sodium hydroxide increases the yield shear value and more than doubles the rigidity, so that an alkaline starch will set harder and will have a better body than an acid starch. The thin boiling starch A will be a thin, fluid paste, in comparison, and tapioca starch will have the best body and the best covering power. CONCLUSIONS 1-The Bingham and Green plastometer is the best type of instrument available for determining the consistency of plastic substances, although there is need of further improvements in methpd so that the values obtained may be independent of the dimensions of the capillary. 2-Adhesives of the concentration in which they are used are mostly plastic, but differences in yield shear value and rigidity of different samples of the same concentration are very striking and significant. 3-Many more results are necessary for a complete understanding of the different products, but it has been shown that the rigidity and yield shear value, as determined by the plastometer, will indicate the body, spreading power, and setting or gelatinizing power of starch and dextrin pastes. Symposium o n Chemistry in Coking a n d Gas Industries, S e w York Meeting, American Chemical Society The fields of coking, gas works control and gas analysis will be discussed by various speakers a t a symposium to be held on Thursday afternoon, September 8. The two hours available for this program as a portion of the Division of Industrial and Engineering Chemistry will be devoted to four principal subjects: coke-oven problems, low temperature carbonization, gas works control, and gas analysis and its applications. If the interest in the program and problems presented a t the symposium seems to justify this, plans may be made for the to deal with t%echemformation of aregular section of the SOCIETY istry of gases and fuels. It is emphasized by the committee in charge of the meeting, Messrs. C. H. Stone, H. E. Howe, and R. S. McBride, that the symposium will deal with the chemical problems rather than with engineering problems which are commonly considered a t the meetings of the American Gas Association. Howevel, it is hoped that the cooperation and attendance of all engineers as well a s chemists will be had. Further suggestions regarding speakers or subjects which receive attention a t the meeting should be addressed t o the secrefary of the symposium, Mr. R. S. McBride, 610 Colorado Building, Washington, D. C. Those having articles which they desire t o present a t the September meeting on any phase of gas or fuel chemistry should send the abstract of their paper with title and author to H. E. Howe, Marine Biological Laboratory, Wood’s Hole, Mass., on or before August 18, in order that their paper may be properly entered on the program. All individual papers on these subjects will be grouped together, probably for presentation on Friday morning following the symposium. The very brief time available for the symposium makes it impossible to include them in the Thursday afternoon session.
