egate and as to how
far it may affect the constitution of the unit groups. That it modifies
the functions or reactivity of the ultimate constituent groups we have
seen from the study of the esters. Thus with the direct ester reactions
the normal fibrous cellulose (C_{6}H_{16}O_{5}) yields a monoacetate,
dibenzoate, and a trinitrate respectively under conditions which
determine, with the simple hexoses and anhydrides, the maximum
esterification, i.e. all the OH groups reacting. If the OH groups are of
variable function, we should expect the CO groups _a fortiori_ to be
susceptible of change of function, i.e. of position within the unit
groups.

But as to how far this is a problem of the constitution or phases of
constitution of the unit groups or of the aggregate under reaction we
have as yet no grounds to determine.

The subjoined communication, appearing after the completion of the MS.
of the book, and belonging to a date subsequent to the period intended
to be covered, is nevertheless included by reason of its exceptional
importance and special bearing on the constitutional problem above
discussed.

~THE ACTION OF HYDROGEN BROMINE ON CARBOHYDRATES.~[4]

H. J. H. FENTON and MILDRED GOSTLING (J. Chem. Soc., 1901, 361).

The authors have shown in a previous communication (Trans., 1898, 73,
554) that certain classes of carbohydrates when acted upon at the
ordinary temperature with dry hydrogen bromide in ethereal solution give
an intense and beautiful purple colour.[5] It was further shown (Trans.,
1899, 75, 423) that this purple substance, when neutralised with sodium
carbonate and extracted with ether, yields golden-yellow prisms of
omega-brommethylfurfural,

CH:C.CH_{2}Br
| |
| O
| |
CH:C.CHO.

This reaction is produced by laevulose, sorbose, cane sugar, and inulin,
an intense colour being given within an hour or two. Dextrose, maltose,
milk sugar, galactose, and the polyhydric alcohols give, if anything,
only insignificant colours, and these only after long standing. The
authors therefore suggested that the reaction might be employed as a
means of distinguishing these classes of carbohydrates, the rapid
production of the purple colour being indicative of _ketohexoses_, or of
substances which produce these by hydrolysis.

By relying only on the production of the purple colour, however, a
mistake might possibly arise, owing to the fact that _xylose_ gives a
somewhat similar co