BY GEORGE BEIMANN, PH.G.
From an Inaugural Essay.
This gum is gathered near the west coast of the Red Sea, further east than the other varieties of gum arabic, and is shipped from the port of Suakin or Savakin, hence its name. It appears in commerce as sub-globular tears, which are more or less broken, have a conchoidal glass-like fracture and, in consequence of numerous fissures, quite opaque. It is imported in considerable quantity and not unfrequently sold for medicinal use.
A mucilage made with 8 ozs. of this gum to one pint of water was. found to be very thick and viscid, a great deal of the gum remaining, as it seemed, undissolved; this was strained out. On diluting the mucilage with water it was noticed that what appeared to be small transparent globules separated, and upon repeated shaking would not dissolve. Some of these globules were collected by diluting the mucilage with water, stirring constantly, allowing to settle, decanting the water, and repeating this operation until all the soluble matter had been removed. The globules were found to be insoluble in boiling water, but on the addition of solution of caustic potassa, or other caustic alkali, they were dissolved, but the salts of the alkalies were without action. A quantity of the globules were spread on panes of glass and dried, yielding thin transparent scales. On boiling these with water they would merely swell up and be transformed into transparent globules again.
These experiments show that they are analogous to and doubtless identical with gummic acid, which seems to pre-exist in the gum, in the free state, and in the mucilage is held in suspension, while from a dilute aqueous solution it separates as colorless globules.
Numerous expedients have been tried to prevent this precipitation, and the only one found successful was to carefully add, before straining, to one-half of the mucilage sufficient solution of caustic potassa to make it very slightly alkaline, then add the other half of the mucilage and shake the mixture well, which should now have a slight acid reaction. After it has stood a little while it can be strained without loss, and may be mixed with water and otherwise used like that prepared from Kordofan gum.
Five grams of the gum were incinerated and yielded .19 gram of ash, equal to 3.8 per cent. Analysis showed the presence of calcium, magnesium and potassium.