1216 THE SUGARS. 



Tunicata (Ascidians) and is closely similar to if not actually 

 identical with vegetable cellulose, but more resistant to the 

 action of acids than is true cellulose. It is coloured blue by 

 the addition of iodine after preliminary treatment with sul- 

 phuric acid. It is soluble in concentrated sulphuric acid, and 

 if water be added to this solution, and it be boiled for some 

 time, a sugar which is apparently identical with ordinary dex- 

 trose is obtained. 



It is prepared in the pure form by treating the mantles for 

 some days with water in a Papin's digester, then in succession 

 with boiling dilute hydrochloric acid, strong caustic potash 

 and water. As thus obtained it retains the form of the parent 

 tissue. 



THE SUGARS. 



The researches of Emil Fischer have thrown a flood of light on 

 the chemistry of the sugars. In phenyl-hydrazine (C 6 H 5 .NH. 

 NH 2 ) he discovered a reagent which forms with the sugars 

 compounds known as hydrazones and osazones. These provided 

 for the first time by their various solubilities, melting-points and 

 rotatory powers an adequate means of detecting, separating and 

 characterizing the several members of this class of carbohv- 

 drates. Hence it became possible to investigate the occurrence 

 of sugars among the complicated products of the reactions 

 employed in the effort to effect their transformations and syn- 

 thetic production. 



The osazones. The compounds of the sugars to which this 

 generic name is applied are formed when solutions of the sugars 

 are warmed for some time on a water-bath with phenyl-hydrazine 

 and dilute acetic acid, and separate out either in an amorphous 

 or crystalline state. As already stated the osazones of the 

 various sugars differ characteristically in their solubilities, 

 melting-points and rotatory powers. They hence afford an 

 invaluable means not only for detecting and isolating the 

 sugars but also for discriminating between sugars whose opti- 

 cal and reducing powers may afford an insufficient distinction. 



Monosaccharides. 



This division of the sugars comprises those which contain 

 from two to nine atoms of carbon, and they may hence con- 

 veniently be called dioses, trioses, tetroses, etc., up to nonoses. 

 The well-known and typical sugar glucose (dextrose) belongs 

 to the hexose group, as also do leevulose and galactose. Re- 

 cently the pentoses have acquired a physiological interest, 

 whereas so far the others, with the exception of the hexoses, 

 are of purely chemical importance. The monosaccharides are 



