210 VEGETABLE MUCILAGE. 



extraction has been complete, the amount of albumen, etc., in the 

 washings must be the same as that in 35 cc. of the first filtrate 

 (which may be calculated from the first estimation) ; but should 

 the washings contain more than the corresponding quantity of 

 filtrate, the excess must be added to the total of the analysis. 



195. Characters of Soluble Mucilage. Apart from their being 

 dissolved by water and precipitated by alcohol from aqueous 

 solution, vegetable gum, arabin, arabic or gummic acid, is also 

 characterized by being converted into glucose when boiled with a 

 dilute acid. It must, however, be observed, that the various 

 arabic acids, according to their origin, yield glucoses differing to a 

 certain .extent from one another, some being more powerfully 

 dextro-, others laevo-rotatory ; some crystallizing with facility, 

 others again not at all, or only with difficulty, or passing first 

 through an intermediate stage as dextrin (according to Kirchner 

 with simultaneous production of cellulose). By means of these 

 properties, vegetable mucilages of particular origin can sometimes 

 be accurately described. Some years ago it was shown by 

 Scheibler 1 that the arabic acid of beet-root yielded, on inversion, 

 a considerable quantity of dextro-rotatory arabinose, which 

 crystallizes with such facility that it was at first thought to be 

 mannite. 



Kiliani has recently asserted the identity of arabinose with 

 lactose. Many varieties of gum arabic also behave like arabic 

 acid, whilst some which are not otherwise distinguishable from 

 good gum, differ in yielding lasvo-rotatory non-crystallizable 

 glucose. In addition to these, B6champ 2 has recently discovered 

 a ' gummicose ' which appears to be allied to galactose ( 205). I 

 am almost inclined to think that a minute investigation of these 

 properties might enable us to distinguish between the various 

 forms of vegetable mucilage soluble in water. 3 



The examination of the oxidation-products obtained by the 



1 Ber. d. d. chem. Ges. vi. 612, 1873 ; Journ. f. pract. Chem. ciii. 458, 

 1868 (Journ. Chem. Soc. xxvi. 1124). See also Neubauer, Jahresb. f . Pharm. 

 6, 1854, and Grseger, ibid. 218, 1872. 



2 Compare Bechamp, Journ. de Pharm. et de Chim. xxvii. 51, 1878. 



3 In general it may be said that the action of dilute acids must be continued 

 for a longer time to convert vegetable mucilage (arabin) into glucose than is 

 necessary for dextrin, triticin, etc. But it must be left for further experi- 

 ments to show to what extent the amount of glucose produced may be taken 

 as an indication of the quantity of arabin originally present. 



