-----------+------+-------------+------------ Gum or | °C. | Ohms | Z Viscosity Mixture. | | Resistance. | at 15° C. -----------+------+-------------+------------- Ghatti, 1 | 10 | 5,667 | 1,490 Ghatti, 2 | 15 | 2,220 | 2,940 Arabic 1 | 15 | 1,350 | 605 Arabic 2 | 10 | 2,021 | 449 Mixture F | 15 | 1,930 | 787 Mixture E | 11.3 | 2,058 | 3,919 -----------+------+-------------+------------- While performing these experiments, an attempt was made to obtain an "ash-free" gum, in order to compare its viscosity with that of the same gum in its natural state. A gum low in ash was dissolved in water, and the solution poured on to a dialyzer, and sufficient hydrochloric acid added to convert the salts into chlorides. When the dialyzed gum solution ceased to contain any trace of chlorides, it was made up to a 10 per cent. solution, and its viscosity determined under 100 mm. pressure, giving the following results at 15° C.: -----------------+--------------+----- -------- | [eta] | Z -----------------+--------------+----- Natural gum..... | 0.05570 | 449 "Ash-free" gum.. | 0.05431 | 438 -----------------+--------------+----- Thus showing that the viscosity of pure arabin is almost identical with that of its salts in gum. The yield of furfuraldehyde by the breaking down of arabin and metarabin was thought possibly to be of some value in differentiating the natural gums from one another, but we have not succeeded in obtaining results of much value. 0.2 gramme of a gum were heated with 100 c.c. of 15 per cent. sulphuric acid for about 2½ hours in an Erlenmeyer flask with a reflux condenser. After this period of time, further treating did not increase the amount of furfuraldehyde produced. The acid liquid, which was generally yellow in color, was then cooled and neutralized with strong caustic soda. The neutral or very faintly alkaline solution was then distilled almost to dryness, when practically the whole of the furfuraldehyde comes over. The color produced by the gum distillate with aniline acetate can now be compared with that obtained from some standard substance treated similarly. The body we have taken as a standard is the distillate from the same weight of cane sugar. The tint obtained with the standard was then compared with that yielded by the gum distillate from which the respective ratios of furfuraldehyde are obtained. The following table shows some of these results: