From observation of the general nature of the solutions of Ghatti gums, and from the fact that when allowed to stand portions of the apparently insoluble matter passed into solution, the hypothesis suggested itself that metarabin was soluble in arabin, although insoluble in cold water. If this hypothesis were correct, it would explain the apparent anomaly of Ghattis giving solutions of higher viscosity than gum arabics, although they leave insoluble matter behind. The increase in viscosity would be due to the thickening of the arabic acid by the metarabin. Moreover, the solutions yielded by various Ghattis leaving insoluble matter behind would _be all of the same kind_, viz., a saturated solution of metarabin in arabin more or less diluted by water. Still further, if the insoluble residue of a Ghatti be the residual metarabin over and above that required to saturate the arabin, then it will be possible to dissolve this by the addition of more arabin in the form of ordinary gum arabic. In order to see if this were the case the following experiments were performed. Equal parts of a Ghatti and of a gum arabic were ground up together and dissolved in water. The resulting solution was _clear_. It was diluted until of 10 per cent. strength, and its viscosity then taken: ---------------------+-------------+----------------+ | Contains 50 per Cent. Ghatti.| ---------------------+-------------+----------------+ A. Pressure 200 mm | [eta] | Z. | Temperature 15° 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° 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: