---------------------+--------------+------------+----------
Sample. | [eta] | [eta] | Z Water
| Uncorrected. | Corrected. | = 100.
---------------------+--------------+------------+----------
Gum arabic.......... | 0.1876 | 0.1856 | 1,233
Cape gum............ | 0.1575 | 0.1555 | 1,029
Indian gum.......... | 0.0540 | 0.0470 | 311
Eastern gum......... | 0.0689 | 0.0639 | 417
Gum arabic.......... | 0.0550 | 0.0480 | 317
Senegal............. | 0.0494 | 0.0410 | 271
Senegal............. | 0.0468 | 0.0380 | 251
Senegal............. | 0.0627 | 0.0557 | 364
Gum arabic.......... | 0.0511 | 0.0430 | 285
Water............... | 0.0149 | 0.0124 | 100
Ghatti.............. | 0.2903 | 0.2880 | 2,322
Ghatti, 5 per cent.. | 0.0903 | 0.0828 | 688
Ghatti, 5 per cent.. | 0.1391 | 0.1350 | 1,089
Ghatti, 5 per cent.. | 0.1795 | 0.1760 | 1,420
Ghatti, 5 per cent.. | 0.1527 | 0.1485 | 1,198
Ghatti, 5 per cent.. | 0.1139 | 0.1083 | 873
Ghatti, 5 per cent.. | 0.1419 | 0.1369 | 1,104
Dextrin............. | 0.0398 | 0.0255 | 169
Dextrin............. | 0.0341 | 0.0196 | 129
Dextrin............. | 0.0455 | 0.0380 | 306
Gum substitute...... | 0.0318 | 0.0224 | 180
Gum substitute...... | 0.0318 | 0.0224 | 180
Amrad............... | 0.0793 | 0.0708 | 570
Australian.......... | 0.0378 | 0.0283 | 228
Australian.......... | 0.0365 | 0.0268 | 216
Brazilian........... | 0.0668 | 0.0627 | 506
Brazilian........... | 0.0516 | 0.0445 | 359
Ghatti.............. | 0.3636 | 0.3621 | 2,920
---------------------+--------------+------------+----------
In the column for [eta] corrected the differences due to the use of
different instruments are of course eliminated. The absolute viscosity
of water at 15° C. determined in four different instruments is shown
below. Poiseuille's value for water being 0.0122.
--------------+-------------+-------------+-------------+-------------+
Instrument. | 1. | 2. | 3. | 4. |
--------------+-------------+-------------+-------------+-------------+
[eta] corrtd. | 0.0109 | 0.01185 | 0.0124 | 0.0120 |
of water. | | | | |
K_{1} value.. | 0.000000898 | 0.000000863 | 0.000000932 | 0.00000052 |
K_{2} value.. | 0.235 | 0.2175 | 0.226 | 0.0204 |
--------------+-------------+-------------+-------------+-------------+
The above values for various gums and dextrins were obtained at a
constant temperature of 15° C. and are compared with water at that
temperature. It is of the utmost importance that the temperature of the
water surrounding the bulbs should be adjusted for each series of
experiments to the temperature at which the absolute viscosity of the
water was determined. As far as we have ascertained, in gum solutions
there is a steady diminution in viscosity with increase of temperature
until a certain temperature is reached, beyond which increase of heat
does not markedly influence the viscosity, and it is possible that above
this "critical point," as we may term it, the gum solutions once more
begin to increase in viscosity. The temperature at which the viscosity
becomes stationary varies somewhat with different gums, but broadly
speaking it lies between 60° C. and 90° C., no gums showing any marked
decrease in viscosity between 80° C. and 90° C.
The experiments we have made in this direction were conducted as
follows. The 300 c.c. bottle containing the gum was placed in a
capacious beaker full of hot water, and the viscosity instrument was
also surrounded with water at the same temperature. Thermometers were
suspended both in the beaker and the outer jar. The viscosity at the
highest temperature obtained, about 90° C., was then taken and repeated
for every fall of 4° C. till the water reached the temperature of the
air.
The values so obtained gradually diminished with the increase of
temperature. From the [eta] values obtained the Z values were
calculated, using water at 15° C. as a standard. From the Z values thus
obtained taken as the ordinate, and the temperature of each experiment
as the abscissa, curves were plotted out embodying the results, examples
of which are given below. The curves yielded by three gums 2, 7, and 8
changed between 90° C and 100° C., while gum sample 4 has a curve
bending between 60° C. and 70° C. Experimentally this increase of
viscosity of the latter gum above 60° C. was confirmed, but the critical
point of the other solutions tried approaches too nearly to the boiling
point of water for experiments to be conducted with accuracy, as the
temperature of the bulbs diminishes sensibly while the experiment is
being made.
If viscosity values have been determined it is possible to calculate the
remaining or intermediate values for Z at any particular temperature
from the general equation--