------------------------+-----------+-----------------------+ | | After heating to | Gum Arabic | Without |-------+-------+-------+ 10 Per Cent. | heat. | 60°C. | 80°C. | 100°C | ------------------------+-----------+-------+-------+-------+ Z at 18°C | 570 | 468 | 470 | 517 | Z at 30°C | 485 | 400 | 422 | 439 | Z at 50°C | 347 | 287 | 258 | 301 | Ghatti gum No. 15, | | | | | 5 per cent. Z at 18°C. | 1,104 | 780 | 660 | 758 | ------------------------+-----------+-------+-------+-------+ The variation of viscosity with strength of solution was also studied with one or two typical gums. A 10 per cent. is invariably more than twice as viscous as a 5 per cent. solution. The following curve was obtained from one of the Ghattis. Similar results were shown by other gums. [Illustration: Variation of Viscosity, with Dilution. Ghatti No. 888.] It would seem, therefore, that strong solutions, say of 50 per cent. strength, would be more alike in viscosity than solutions of 5 per cent. strength of the same gums. In other words, the viscosity of a gum solution should be taken as nearly as possible to the strength it is used at, to obtain an exact quantitative idea of its gumming value. The observation of this fact was one of the circumstances which decided us to use 5 per cent. solutions for the determination of Ghatti gum viscosities, the ratio between the 5 per cent. and 10 per cent. solutions of gum arabics being roughly the same as that between the respective weights required for gumming solutions of equal value.