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PDFEFFECT OF TEMPERATURE UPON VISCOSITY.—GUM VIII.
------------+------+--------+-------------| Temperature.| [eta]|Z found.|Z calculated.| ------------+------+--------+-------------| deg.C. | | | | 50 |0.0430| 347 | 347 | 46 |0.0475| 383 | 371.14 | 42 |0.0502| 405 | 397.09 | 38 |0.0510| 411 | 424.73 | 34 |0.0575| 463 | 454.06 | 30 |0.0602| 485 | 485 | 26 |0.0637| 513 | 517.82 | 22 |0.0667| 538 | 552.25 | 20 |0.0707| 570 | 570 | 18 |0.0755| 609 | 583.07 | ------------+------+--------+-------------+
The constants for the first gum are those given in the preceding column, while for the latter they were—
A = 771.9: B = -11.15: C = 0.053
As will be observed, the effect of heat appears to be the same upon the two typical gum arabics quoted above, an increase of temperature from 18 deg. C. to 50 deg. C. decreasing the viscosity by nearly one half in both cases, and the same seems to be true of most gum arabics. Roughly also the same holds good for Ghattis, as the following numbers show:
------------+-------------+------------| Gum. | Z at 18 deg. C. | Z at 50 deg. C.| ------------+-------------+------------| Gum arabic. | 1016 | 579 | Gum arabic. | 428 | 228 | Gum arabic. | 609 | 347 | Gum arabic. | 581 | 258 | Ghatti. | 572 | 306 | Ghatti. | 782 | 418 | ---------------------------------------+
The following table shows the effect of heat upon the viscosity of a typical Ghatti:
GHATTI GUM NO. 15.—VISCOSITY.
------------+------+-----| Temperature.| [eta]| Z. | ------------+------+-----| deg.C. | | | 50 |0.0517| 418 | 46 |0.0581| 468 | 42 |0.0628| 506 | 38 |0.0726| 585 | 34 |0.0788| 635 | 30 |0.0857| 691 | 26 |0.0889| 717 | 22 |0.0919| 741 | 20 |0.0946| 763 | 18 |0.0964| 777 | ------------+------+-----+
There is therefore no essential difference in the behavior of a Ghatti and a gum arabic on heating. Some interesting results, however, were obtained by heating gums, both Ghattis and arabics, at a fixed temperature for the same time, cooling, and then after making the solutions up to the original volume taking their viscosities at the ordinary temperature. The effect of heating for two hours to 60 deg. C., 80 deg. C., or 100 deg. C. was a small permanent alteration in viscosity of the solution, and it would therefore seem desirable that gum solutions should be made up cold to get the maximum results. The following numbers illustrate this change, viz.:
