+
A. Pressure 200 mm | [eta] | Z. |
Temperature 15 deg. C | 0.2517 | 2,030 |
---------------------+-------------+----------------+

The viscosity of this solution therefore was considerably greater than
the mean viscosity of the 10 per cent. solutions of the Ghatti and the
gum arabic, viz., (0.288 + 0.0636)/2 = 0.1758 for the calculated [eta].
Hence it is evident that the increase in viscosity is due to the
solution of the metarabin.

Next a solution was made from a mixture of 70 per cent. Ghatti and 30
per cent. gum arabic. This was also clear and gave a considerably higher
viscosity than the previous solution.

---------------------+------------------------------+
| Contains 70 per Cent. Ghatti.|
---------------------+-------------+----------------+
B. Pressure 200 mm | [eta] | Z. |
Temperature 15 deg. C | 0.3177 | 2,562 |
---------------------+-------------+----------------+

It will be obvious that the increase of viscosity over the previous
solution in this case must be due to the smaller amount of the thin gum
arabic which is present, _i.e._, in the first case there is more gum
arabic than is required to dissolve the whole of the insoluble
metarabin. Further experiments showed that this is also true of the
second mixture, as the viscosities of the following mixtures
illustrate:

-------------------------+--------+-------+
Strength of Solution. | [eta] | Z. |
-------------------------+--------+-------|
C. 80 per cent. Ghatti. |0.3642 | 2,937 |
D. 75 per cent. Ghatti. |0.33095 | 2,669 |
E. 77.5 per cent. Ghatti.|0.4860 | 3,819 |
-------------------------+--------+-------+

This last solution E we called for convenience the "maximum viscosity"
solution, as we believe it to be a 10 per cent. solution containing
arabin very nearly saturated with metarabin. As will be observed, its
viscosity differs widely from those of solutions C and D, between which
it lies in percentage of Ghatti. The first named solution C contains
_too little_ of gum arabic to dissolve the whole of the metarabin.
Consequently there is a residue left undissolved, which of course
diminishes its viscosity. The second solution D is too low in viscosity,
as it still contains too much of the weak gum arabic, and as will be
seen further on, a very slight change in the proportions increases or
decreases the visco