THE NITKOGEN-FREE EXTRACT OF FEEDING STUFFS. G45 



MONOSACCIIAIUUS OF OTUHK rOMl'OSlTIOXS AND TIIKIK DKlUVATn'KS. 



Aside from the liexoses eimmerated and the substances which yield 

 hexoses (dextrose, luannose, galactose, levulose) by hydrolysis, the 

 nitrogeu-free extract may coutain derivatives of theoretical hexoses,' 

 and of monosaccharids of other series, notably of the pentoses (C.-,HioOs), 

 and probably also those of the tetroses (O4H1JO4), the heptoses (OvIIuO^), 

 etc., although none of the latter have as yet been found in plants. The 

 derivatives of these special (theoretical) monosaccharids occurring in 

 plants coutain less water than the hexoses, and are derived from the 

 latter by the loss of one molecule of water. Their names are formed 

 by adding the syllable an to the name of the mouosaccharid, as C4HoOa 

 tetrosau, C5H(!04 pentosan, O7H12OG heptosau, etc. 



Fcnto.se.s and pentosans. — The pentoses are sugars having the formula 

 O5H10O-, from which they derive their name. Their derivatives, which 

 are formed from them in the same way that starch is from glucose, i. c, 

 by the loss of water, are the pentosans, C5Hj|()4. 



According to E. Fischer's comi^reheusive theory, there are 8 pen- 

 toses.^ Of these, 2 have as yet been found in nature, namely, arabinose 

 and xylose (wood sugar). These 2 sugars are not knowu to occur as 

 such, but as pentosans, namely, as arabau and xylan (wood gum). 



Arabinose, discovered by Scheibler, is prepared from gum arable, 

 cherry gum, beet pith, and other substances which contain araban, 

 by treating these materials with dilute sulpliuri<; acid and thus hydro- 

 lyzing the arabau to arabinose.' Xylose, discovered by Koch and 

 further investigated by Wheeler, Allen, and Tollens,'' is obtained from 

 substances which contain xylan (wood gum), as for example, wood and 

 straw. It is most easily obtained from wood by extracting the xylan 

 with sodium hydroxid and then hydrolyzing this with acid. 



Formerly the pentoses were not distinguished from common sugars 

 or hexoses, because they are very similar to these, and more especially 

 because, like these, they reduce I'ehling's solution. Since the above- 

 mentioned investigations on xylose the pentoses have been industri- 

 ously searched for, and especially since Stone and Tollens demonstrated 

 that the formation of furfurol from the pentoses and pentosans by distill- 

 ing with acid is a characteristic reaction for these substances. Besides 

 this reaction there are others equally characteristic, namely, the red 

 coloration when pentoses or pentosans are heated with hydrochloric 

 acid and phloroglucin, and the constant spectral absorption of this solu- 

 tion.-^ These reactions enable the detection of ^■ery small amounts of 

 pentoses, and are taken advantage of in their <iuantitive determination.'' 



'See reference to E. Fischer's investigations in 'rollens' Kurzes Handbucli der 

 Kobleuliy (Irate, vol. 2, \k 14. 



-Tollens' Kurzes Haiidl)ucli der Kohlenliydrato, vol. 2, p. 21. 



^Stoue and Tollens, Liebig's Ann. Cheui., 249 (1888), pp. 238, 267. 



'Liebig's Ann. Cheni., 254 (1889), p. 316. 



'^■Wheeler, Allen, and Tollens, Liebig's Ann. Chem., 254 (1889), pp. 260, 289, .304. 



"Investigations of Stone, do Clialniot, Flint, Miinn, and Kriiger, all of which 

 except some recent work by Stone and do Chalmot were carried on under the dircc- 

 tiyu of the writer. 



