----------------------+------------+-----------+
-----         | 13.3 per Cent.  Ghatti. |
----------------------+------------+-----------+
F. Pressure 200 mm.   |      [eta] |     Z.    |
Temperature 15 deg.  C. |     0.0976 |    787    |
----------------------+------------+-----------+

----------------------+------------+-----------+
-----         | 86.6 per Cent.  Ghatti. |
----------------------+------------+-----------+
G. Pressure 200 mm.   |      [eta] |     Z.    |
Temperature 15 deg.  C. |     0.4336 |   3,497   |
----------------------+------------+-----------+

This latter solution is approaching fairly closely to our “maximum viscosity” with the previous Ghatti, and probably a very slight decrease in the amount of gum arabic would bring about the required increase in viscosity.

When these experiments were first commenced we were still under the impression, which several months’ experience of working with gums had produced, namely, that the Ghattis were quite distinct in their properties to ordinary gum arabics.  But the new hypothesis, and the experiments undertaken to confirm it, showed clearly that if the viscosity of a gum solution depends on the ratio of metarabin to arabin, then there is no absolute line of demarkation between a Ghatti and a gum arabic.  In other words, there is a constant gradation between gum arabic and Ghattis, down to such gums as cherry gum, consisting wholly of metarabin and quite insoluble in water.  Therefore those gum arabics which are low in viscosity consist of nearly pure arabin, while as the viscosity increases so does the amount of metarabin, until we come to Ghattis which contain more metarabin than their arabin can hold in solution, when their viscosity goes down again.

From these observations it would follow, that by taking a gum of less viscosity than the gum arabic previously used to dissolve the Ghatti, less of it would be required to do the same work.  We confirmed this suggestion experimentally by taking another gum arabic of viscosity 0.0557 at 15 deg.  C. A mixture containing 93.3 per cent. of this Ghatti and 6.7 per cent. of our thinnest gum arabic gave a clear solution which had the highest viscocity we have yet obtained for a 10 per cent. solution.

----------------------+--------+-------+
H. Pressure 200 mm.   |  [eta] |   Z.  |
Temperature 15 deg.  C. | 0.5525 | 4,456 |
----------------------+--------+-------+

This gum arabic may be regarded as nearly pure arabin (as calcium and potassium, etc., salt).  By diluting the new “maximum viscosity” solution, therefore, with the 10 per cent. solution of the gum arabic in fixed proportions we obtain a series of viscosities which are shown in the following curve.

[Illustration:  Curve Showing Influence of Ghatti upon Viscosity.]

Besides obtaining this curve for change in viscosity from maximum amount of metarabin to no metarabin at all, we also traced the decrease in viscosity of the “maximum” solution by dilution with water.  The following numbers were thus obtained, and plotted out into a curve.