600 THE GUM PERMKINTATION OF SUGAR CANE JUICE, 



Basic lead acetate makes the solution more opaque, but does 

 not coagulate the gum. Lime water gives no precipitate. It 

 has been already shown that it is coagulated by milk of lime, but 

 not b}^ mercuric nitrate, magnesium oxide, or magnesium sulphate. 

 Barium hydrate forms a curdy precipitate, whicli is decomposed 

 by carbon dioxide. A precipitate is also obtained on adding 

 ammoniacal lead acetate. Dilute sodium hydrate is apparently 

 without effect, but the strong hydrate (10 %) slowly makes the 

 solution clear and limpid. Neither iodine, tannic acid, nor ferric 

 chloride react with solutions of medium strength. When heated 

 in steam for a few hours with dilute nitric acid (2-1), oxalic and 

 tartaric acids are obtained in quantity. Mucic acid is not pro- 

 duced, even when oxidation is effected at lower temperatures. 



On heating the dry and powdered gum in capillary tubes, it 

 begins to darken in colour at 160° C. At 183° it shows signs of 

 melting ; at 193° the fragments have become soft and adherent, 

 and begin to rise in the capillary tube, apparently the result of 

 decomposition and evolution of water. At 198° the steam 

 bubbles are well marked, and at 200° the gum melts to a trans- 

 parent brown frothy mass. The brown pyro- substance dissolves 

 readily in water, forming a brown solution like the colour of 

 neutral ferric chloride. It is not precipitated from solution by 

 alcohol at once, although in time a slight sediment settles out. 

 Neither is it precipitated by barium hydrate nor basic lead 

 acetate. It does not reduce Fehling's solution, but reduction is 

 obtained on hydrolysing the body with dilute acids. 



The natural gums are substances allied to the carbohydrates; 

 they are of a faintly acid nature and occur combined with alkaline 

 and earthy bases. For example, O'Sullivan has shown that a 

 Gedda gum consists of the calcium, magnesium and potassium 

 salts of four geddic acids."^ The gum acids combine with bases 

 to form well defined compounds, the barium one being the most 

 easily prepared. 



Following the method recommended by O'Sullivan for the 

 preparation of the gum acid, the bacterial gum was dissolved in 



* O'Sullivan, Trans. Chem. Soc. 1891, 1071. 



