---------------------+-------------+----------------+
| Contains 50 per Cent.  Ghatti.|
---------------------+-------------+----------------+
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 viscosity enormously.

We next tried a series of similar experiments with a Ghatti containing far less insoluble residue and which consequently would require less gum arabic to produce a perfect solution.  Mixtures were made in the following proportions, viz.: