, for example,
may be illustrated as follows:

Glucose (C_{6}H_{12}O_{6}) Methyl Glucoside (C_{7}H_{14}O_{6})
CHO CHO
| |
(CHOH)_{4} (CHOH)_{4}
| |
CH_{2}OH CHOH
|
CH_{3}

A general formula for glucosides is R.(CHOH)_{5}.CHO; and the R may
represent a great variety of different organic radicals (see the chapters
dealing with Glucosides and with Tannins). When the glucosides are
hydrolyzed, they yield glucose and the hydroxyl compound of the radical
with which it is united. All the statements which have been made with
reference to glucosides, apply equally well with reference to fructosides,
galactosides, mannosides, etc.

It is possible, by various laboratory processes, to replace additional
hydrogen atoms in the glucose molecule with the same or other organic
radicals, thus producing glucosides containing two or more R groups; but
most of the natural glucosides contain only one other characteristic group.

=Oxidations.=--When the hexoses are oxidized they give rise to three
different types of acids, depending upon the conditions of the oxidation
and the kind of oxidizing agent used. With glucose, for example, the
relationships involved may be illustrated as follows:

CHO COOH CHO COOH
| | | |
(CHOH)_{4} (CHOH)_{4} (CHOH)_{4} (CHOH)_{4}
| | | |
CH_{2}OH CH_{2}OH COOH COOH
Glucose Gluconic acid Glucuronic acid Saccharic acid

An important property of the acids of the _gluconic_ type is that when
heated with pyridine or quinoline to 130 deg.-150 deg. they undergo a
molecular rearrangement whereby the acid corresponding to an isomeric
sugar is produced. For example, gluconic acid, under these conditions,
becomes mannonic acid, which can be reduced to mannose. The process is
reversible; mannose can be converted to mannonic acid, thence to gluconic
acid, thence to glucose. Similarly, galactonic acid can be converted into
talonic acid, and this to talose, and this process is reversible. These
facts a