Having obtained this curve, we are now in a position to follow up the hypothesis by calculating the surplus amount of insoluble matter in a Ghatti.  For, let it be conceded that the solution of any Ghatti leaving an insoluble residue is a mixture of arabin and metarabin in the same ratio as our “maximum” solution, only more diluted with water, then from the found viscosity we obtain a point on the curve for dilution, which gives the percentage of dissolved matter.

Now to show the use of this:  The Z value for a 10 per cent. solution of the second Ghatti at 15 deg.  C. is 2,940.  This corresponds on the curve to 8.4 dissolved matter. 10 — 8.4 = 1.6 grammes in 10 grammes, which is insoluble.

CHANGE OF VISCOSITY WITH DILUTION—­“MAXIMUM” SOLUTION. 15 deg.  C. TEMPERATURE.

------------+--------------+---------
Percentage. | [eta]        |     Z.
------------+--------------+---------
10      |    0.55250   |   4,456
9      |    0.42850   |   3,456
8      |    0.35120   |   2,832
7      |    0.27660   |   2,230
6      |    0.22290   |   1,797
5      |    0.16810   |   1,355
4      |    0.11842   |     955
3      |    0.08020   |     647
2      |    0.06190   |     499
1      |    0.03610   |     291
------------+--------------+---------

[Illustration:  Curve of Variation in Viscosity on Dilution of the “Maximum” Solution.]

We have already shown that a “maximum” viscosity solution of this gum is formed when 6.7 per cent, of thin gum arabic is added to it, and therefore 6.7 parts of a thin gum arabic are required to bring 16 parts of metarabin into solution.  A convenient rule, therefore, in order to obtain complete solution of a Ghatti gum is to add half the weight in thin gum of the insoluble metarabin found from the viscosity determination.  But the portion of the gum which dissolved is made up in a similar manner (being a diluted “maximum” solution).

Therefore the 84 per cent. of soluble matter contains 58 parts of metarabin, and the total metarabin in this gum is 58 + 16 = 74 per cent, on the dry gum.

With these solutions of high viscosity some other work was done which may be of interest.  The temperature curves of the mixtures marked E, G, and F were obtained between 60 deg.  C. and 15 deg.  C. The two former curves showed a direction practically parallel to that at the 10 per cent. solutions, and as they were approaching to the “maximum” solution, this is what one would expect.  Mr. S. Skinner, of Cambridge, was also good enough to determine the electrical resistances of these solutions and the Ghattis and gum arabics employed in their preparation.  The electrical resistance of these gum solutions steadily diminishes as the temperature increases, and the curve is similar to those obtained for rate of change with temperature.  Although the curves run in, roughly, the same direction, there does not appear to be any exact ratio between the viscosities of two gums say at 15 deg.  C. and their electrical resistances at the same temperature; hence it would not seem possible to substitute a determination of the electrical resistance for the viscosity determination.  The results appear to be greatly influenced by the amount of mineral matter present, gums with the greatest ash giving lower resistances.