322 ON THE PURIFICATION OF GUM ARABIC. 
matter remains united, carbonic acid gas is evolved, and the 
liquid remains nearly colorless. Then it is filtered through 
some very close filters, such as would not allow the pas- 
sage of any particle of solid matter, and thereby a pure, 
limpid, and tasteless solution of gum is obtained. Some- 
times the whole of the coloring matter has not been re- 
moved, and a repetition of the process is necessary to obtain 
a perfect whiteness. The purified filtered solution is then 
concentrated by evaporation at a moderate temperature, 
and reduced to any required degree of density, or to com- 
plete dryness. I have constantly found that none of the 
physical and chemical properties of the gum thus operated 
upon are in any way affected. 
There is also another method of separating the acid from 
the gum in solution, equally effective, but a small portion 
of coloring matter remains in the gum ; it is by boiling the 
mixture in vacuum at a temperature i nder 120° Fahr. The 
gas which is volatilized may be absorbed by charcoal placed 
in the receiver, or may be conducted through a pump into 
another receiver containing water. The solution of gum, 
when the process is finished, remains free from acid, if 
during the whole operation it has been well protected from 
contact with the atmospheric air. 
The process described may be varied in its details, but its 
principles remain essentially the same; and the gum obtain- 
ed, after filtration, is not found to contain the slightest par- 
ticle of any of the ingredients used, and is undoubtedly 
purer and whiter than the finest sample of the picked white 
Turkey gum. 
Now, I may be allowed to add a few remarks, consider- 
ing the matter in a commercial point of view. At present, 
the white gum Arabic is a scanty product of nature ; we 
are dependent for its supply upon the one country, (Egypt,) 
which alone produces the article ; frequently French or 
Austrian merchants established at Alexandria make a mono- 
