BY R. GREIG SMITH. 393 



O'SuUivan* has shown that fragments of the same gum contain 

 gum acids which rotate the ray of polarised light to dififerent 

 extents. He also showed that diiferent kinds of gum of the 

 arabin group have rotations in different directions; for example, 

 gum arabic is Isevo-rotatory, Gedda gum is generally dextro- 

 rotatory, and an Australian gum was optically inactive. It is 

 therefore probable that the gum acids of the natural gum and 

 those of the bacterial gum would differ in their optical activitj^, 

 since the conditions under which the gums had been produced 

 had been so very different. This proved to be the case. I pre- 

 pared the gum acids from the gum of A. hinervata and from 

 cultures of Bact. acacice and submitted them to Mr. T. U. Walton, 

 B.Sc, of the Colonial Sugar Refining Co., who found that the 

 natural gum acids had a specific rotation of [«]d = +0°-9 and 

 the bacterial gum acids had a rotation of [a]^, = + 43°. I do not 

 lay any stress upon the difference in the optical activities. In 

 the future I shall grow the bacterial gum in different ways and 

 from different materials, to see how the optical activity is thereb}'- 

 influenced. 



A portion of the sugar-free gum acids was dissolved in 15 c.c. 

 of water, and to this 10 c.c. of 5 % sulphuric acid was added, thus 

 making a 2 % solution. This was heated on the water bath for 

 an hour to hydrolyse the combined arabinan. Subsequent work 

 showed that this heating might with advantage be prolonged for 

 three or four hours to hydrolyse the arabinan more completely. 

 After the digestion with the 2 % acid the solution was cooled 

 and the unaltered gum acids precipitated with alcohol. The 

 solution, after filtration, was distilled until most of the alcohol 

 had been removed; the residual fluid was, after the addition of 

 about 50 c.c. of water, neutralised with barium carbonate and 

 filtered. The filtrate was boiled down to one-half and clarified 

 with aluminium hydrate. The clear solution was used for the 

 preparation of the osazone. 



* O'Sullivan, .Journ. Chem. Soc. 1891, 1029. 



