REACTIONS OF THE MONOSACCHARIDES. 7 
Its crystals, which arc difficult to obtain, are partly water-free 
(CgH^Og) and partly contain water of crystaDisation (2C 6 H 12 6 .H 2 0). 
Levulose is different in chemical constitution from tl fcher sugars we 
have studied in this group. It. however, gives the same general tests; 
but its specific rotatory power has not been satisfactorily determined. 
Galactose, is obtained by the hydrolytic decomposition of lactose or 
milk-sugar, and from many other carbohydrates, especially gums and 
mucilages. It is obtained by bhe decomposition of a glucoside occurring 
in the brain called cerebrin. 1 It crystallises in needles or plates, which 
melt at L68 C. It is somewhat more difficult of solution in water than 
dextrose, and more strongly dextrorotatory. 
Mannose or seminose is another monosaccharide which is of scientific 
interest, as it is the aldehyde of the alcohol (mannite) of which levnlose is the 
corresponding ketone. 
It does not occur free in nature. It is obtained from mannite by 
oxidation,- and also by the action of dilute sulphuric acid on the so-called 
reserve cellulose. 3 
Reactions of the monosaccharides. — (a) Fermentation. — They are 
directly fermentable by yeast into alcohol and carbonic acid (C H 1; ,() r , 
= 2C 2 Hg.OH+2C0 2 ) ; and by the Boric, -in m lac tit into lactic acid (C G H 12 O c 
= 2CH 3 — CH.OH. — COOH). But this property of fermentation is only 
possessed by those which occur in nature. 
(b) Beducing power. — Being aldehydes or ketones, they are easily 
oxidisahle, and reduce metallic oxides in alkaline media. 
They cause a deposition of metallic silver in an ammoniacal silver solution 
containing some caustic soda ; and of metallic bismuth from basic bismuth 
nitrate suspended in soda (Bbttcher's test) ; and of the red cuprous oxide (Cu 2 0), 
or of the yellow cuprous hydrate Cu(OH 2 ), from an alkaline solution of eupric 
oxide, as in Trommer's and Fehling's tests. 4 
(c) "When heated in the dry state, before they char, they yield a 
brownish product called caramel. A similar substance is formed by 
boiling with alkalies (Moore's test). 5 In the brown substance formed, 
among other bodies is levulinic acid, CH 3 — CO — CH 2 — CH. 2 — COOH. 
its rotatory power weak («d - 26) ; it forms an osazone. Neubauer and Vogel 
(" Anleitung zar qualitative!] und quantitative!! Analyse desHarns," 1890) suggest the name 
"laiose " for it. 
1 Thierfekler, Ztschr. f. physiol. Ohem., Strassburg, Bd. xiv. S. 209; Brown and 
Morris, Proc. Chan. Soc., London, 1889, p. 167. 
2 Fischer and Hirschberger, Ber. d. devtsch. chem. Gesellech., Berlin. Bde. xxi. S. 1805 ; 
xxii. S. 1155 and 3218. 3 Reiss, ibid., Bd. xxii. S. 909 and 3218. 
4 In Allihu's method (Jov/rn. f. prakt. Chem., Leipzig, Bd. xxii. S. 55) of estimating 
the reducing power of a sugar, the cuprous oxide obtained by Fehling's method is collected 
and weighed as metallic copper. Pfliiger (Arch. f. d. gcs. Physiol., Bonn, 1877, Bd. Ixvi. ) 
recommends that the cuprous oxide should be dried at 120' and weighed. O'Sullivan and 
Stern (Journ. Chem. Soc, London, 1896, p. 1691), who have recently prepared dextrose 
from several sources, have found that 1 gr. of CuO is reduced by 0'4535 gr. of dextrose 
(1 gr. Cu.,O = 0"5O45 gr. dextrose). On the relation between reducing power and specific 
rotation see a series of papers by H. T. Brown, G. H. Harris, and J. H. Millar (Proc. 
Chem. Soc, London, 1896, pp. 211-244). If the reducing power of dextrose is taken as 
100, that of levulose is 92 to 94 (ibid., 1897, p. 4). 
5 F. Framm (Arch. f. d. gcs. Physiol., Bonn, 1896, Bd. lxiv. S. 575) has found that 
Moore's test is accompanied by the formation of products of oxidation, namely aldehyde 
and formic acid. 
