p to a certain point, and then a gradual increase. A
comparison of some of the figures actually obtained in some of these
experiments, compared with the calculated figures for the same
temperature, shows their general agreement.

[Illustration: Curves showing viscosity change with temperature for
three typical gums. A--Arabic VII. B--Senegal VIII. C--Ghatti 15.]

EFFECT OF TEMPERATURE UPON VISCOSITY--GUM VII.

------------+------+--------+-------------+
Temperature.| [eta]|Z found.|Z calculated.|
------------+------+--------+-------------+
deg.C | | | |
50 |0.0283| 228 | 228.00 |
45 |0.0305| 246 | 246.55 |
42 |0.0352| 284 | 266.75 |
38 |0.0368| 297 | 289.00 |
34 |0.0410| 330 | 313.06 |
30 |0.0419| 339 | 339.00 |
26 |0.0445| 359 | 367.80 |
22 |0.0492| 398 | 396.47 |
20 |0.0511| 412 | 412.00 |
18 |0.0531| 428 | 428.00 |
------------+------+--------+-------------+

EFFECT 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