LEGUMINOSH. a8 
q of olive-green or brownish-gréen matter; after filtration the 
_ mucilage is similar in colour to that of gum arabic. 
_ Commerce.—Akakia is imported from the Red Sea ports, and 
__ is kept by all Mahometan druggists; it occurs in bladders con- 
_ taining 5 to 6 ounces each, 
Chemical composition of Gum.—The levorotatory gums are 
: principally potassium, magnesium, and calcium salts of arabic 
or allied acids; they contain from 12 to 18 per cent. water, and 
_ yield 2°7 to 3-0 per cent. of ash consisting almost wholly of 
carbonates of these metals. Arabic acids (C'? H*? O'!) has 
_ been isolated from the so-called East Indian gum. (0’Sullivan.) 
For the method of preparing it see (Watt’s Dict. of Chem. by 
— Morley and Muir, ii., 295.) When slowly dried out of syrupy 
solutions, on glass plates, it is a brittle, transparent, colourless, 
glassy body, soluble in water. During desiccation, especially — 
if a little mineral acid be present, the acid is frequently con- 
~ verted into the meta modification. Solutions of arabic acid 
- are strongly acid to litmus paper, and have a sharp acid taste ; 
they completely neutralise solutions of the alkalies and alkaline 
earths, and decompose carbonates. The salts cf the alkaline © 
addition of stronger acids. Ba SO*, PbS, and other sulphides, 
and some hydrates precipitated in solutions of arabic acid, can- 
not be filtered out, but pass), in greater part, through the filter. 
Gum arabic prevents the precipitation of the alkaloids by 
phosphomolybdic acid, potassium-mereury iodide and tannin. 
_ (Lefort et Thibault.) These are properties common to all the 
gum acids. ‘he defining characters of arabic acid are its 
optical activity, viz. [a] j= — 26° to 28°, for solutions contain- 
ng 5 to 6 grams dry substance in 100 c.c., and the composition 
ts neutral barium and calcium salts; in the dry state, the 
er contains 6-0 per cent. BaO and the latter 2°28 per cent. 
(O’Sullivan.) Solid gum roasted with oxalic acid 
a 
