336 The Dejtrose-Lacvidos^c Ratio in the Mauijold 



a rotation + 0-039° (in 200 nun. tube at 20°) is obtained, whereas the 

 rotation actually observed, after allowing for the cane sugar and pentoses, 

 was + 0-093° (pentoses as arabinose) or + 0-125° (pentoses as xylose). 

 Thus in the two cases a posilire rotation remains unaccounted for, of 

 + 0-054° or +0-086° respectively. Similarly at 4 p.m., the whole of 

 the reducing sugars calculated as dextrose w-ould barely account for 

 the actual positive rotation observed if the pentoses be taken as xylose, 

 the excess being + 0-004°; if, however, the pentoses be taken as 

 arabinose, the dextrose would more than account for the rotation ob- 

 served by + 0-037°, and in this case the dextrose becomes 0-92 per cent. 



and laevukjse 0-21 per cent., the ratio y being 4-34. Similarly at 8 p.m. 



the assumption that the whole of the reducing sugar is dextrose leaves 

 + 0-008° unaccounted for if the pentose is xylose; when it is taken as 



arabinose, D becomes 0-73 and L = 0-14 per cent., the ratio y being 



high, viz. 5-33. Similar observations hold for midnight, 2 a.m. and 4 a.m. ; 

 at 4 a.m. the quantity of reducing sugars is so small, that assuming the 

 pentose to be arabinose causes the laevulose to appear in excess, whilst 



if it is taken as xylose, the dextrose appears largely in excess, j being 



7-14. 



It is clear therefore that little significance can be attached to the values 

 for dextrose and laevulose in Series I owing to the presence of a dextro- 

 rotatory impurity^, the rotation of which is large relatively to that of 

 the small quantity of sugars present. Even though this is the case, 

 between 8 a.m. and 2 p.m. the values of dextrose and laevulose are 

 approximately equal, especially when the pentoses are assumed to be 



arabinose, the ratio y being approximately 1. It should be noted 



> A determination was made foi us by Mr E. Horton of the aminonitrogen in the 

 Solution ^4 used in estimating tlie sugars in tlio ease of a .sample of mangold leaves pieked 

 at 2.45 p.m. on October 8tli, 1914. 2 c.c. of this .solution gave in the van Slyke micro- 

 apparatus 0-225 e.c. of nitrogen at and 760 representing 0007 grm. of aminonitrogen 

 per 100 c.c. Calculated as ijlulumine this would represent 1-2 per cent, of glutamino on 

 the total vacuum-dried weight of the leaf at a time of day when, judging by the results 

 of Table III, the proportion of such impurity is at its minimum ; in this picking, the cane 

 sugar was 7-5 per cent, and the hexoses 19-1 per cent, of the total vacuum-dried matter, 

 so that the proportion of the optically active amide is in this case only small relatively 



to the sugars, a fact which would explain lluit the ratio . keeps in the neighbourhood of 

 unity (SCO Tables II and III). 



