BY R. GREIG SMITH. 601 



water and dialysed until free from phosphoric acid after which 

 the faintly acid solution was neutralised with baryta water. A 

 very small quantity (less than 1 c.c.) was required, and the 

 solution appeared to be unaltered and when treated with dilute 

 alcohol did not flocculate. A better result was obtained on 

 adding an excess of baryta water, when there formed a bulky 

 curdy precipitate which rapidly settled. From this behaviour it 

 would appear that the bacterial gum is more nearly related to the 

 starches than to the true gums, such as gum arable. When no 

 further precipitate was formed the compound was rapidly filtered 

 and washed with water, then with alcohol, until the washings 

 were free from barium. The precipitate was dried in vacuo over 

 sulphuric acid, then powdered and finally dried at 100° in a 

 current of dry, CO^-free air under 100-120 mm. pressure. This 

 method differs from O'SuUivan's in the addition of an excess of 

 baryta water, and it seemed possible that a definite compound 

 might not be formed. To test the matter a sample of gum was 

 divided unequally and each portion was acidified, dialysed, pre- 

 cipitated with excess of baryta water, filtered, washed and dried 

 as described above. The barium in a part of each portion was 

 estimated by precipitation with sulj^huric acid and the following 

 results were obtained : — 



1st portion— 1-49 15 grms. gave 0-4505 grm. BaSO^ = 19-84% BaO. 

 2nd portion—l-5765grms. gave 0-4766grm.BaSO4 = 19-86 %BaO. 



These results are very close and undoubtedly prove that when 

 baryta is added in the manner indicated a definite compound is 

 formed. It would also appear that the barium oxide is present 

 in the same proportion as in the compound formed by adding 

 baryta water to starch. Asboth"^ found that the starch compound 

 contained 19-97% BaO, and he considered that this agreed fairly 

 well with the formula C,4 H40 O^ BaO, which theoretically 

 requires 19-10% BaO. 



The Origin of the Gum. 



Marshall Ward and Reynolds Green in discussing the action 

 of a gum bacterium isolated by theih considered it possible that 



* Asboth, Analyst, xii., 138. 

 40 



