Dictionary of Chemistry [6th Ed.]

bonds, whereas starch is composed

of 1-4 α-glycosidic bonds.

glycosidic linkSee glycoside.

glycosylationThe process in

which a carbohydrate is joined to an-

other molecule, such as a protein to

form a *glycoprotein or to a lipid to

form a glycolipid (see glyceride). Gly-

cosylation occurs in the rough endo-

plasmic reticulum and the Golgi

apparatus of cells.

glyoxal(ethanedial)A low melting-

point yellow crystalline solid, CHO-

CHO, m.p. 15°C. It is a dialdehyde. It

gives off a green vapour when heated

and burns with a violet-coloured

Ûame. Glyoxal is made by the cat-

alytic oxidation of ethanediol and is

used to harden the gelatin employed

for photographic emulsions.

goethiteA yellow-brown mineral,

FeO.OH, crystallizing in the or-

thorhombic system. It is formed as a

result of the oxidation and hydration

of iron minerals or as a direct precip-

itate from marine or fresh water (e.g.

in swamps and bogs). Most *limonite

is composed largely of cryptocrys-

talline goethite. Goethite is mined as

an ore of iron.

Golay cellA transparent cell con-

taining gas, used to detect *infrared

radiation. Incident radiation is ab-

sorbed within the cell, causing a rise

in the gas temperature and pressure.

The amount of incident radiation can

be measured from the pressure rise

in the tube.

goldSymbol Au. A soft yellow mal-

leable metallic *transition element;

a.n. 79; r.a.m. 196.967; r.d. 19.32;

m.p. 1064.43°C; b.p. 2807± 2 °C. Gold

has a face-centred-cubic crystal struc-

ture. It is found as the free metal in

gravel or in quartz veins, and is also

present in some lead and copper sul-

phide ores. It also occurs combined

with silver in the telluride sylvanite,

(Ag,Au)Te 2. It is used in jewellery,

dentistry, and electronic devices.

Chemically, it is unreactive, being

unaffected by oxygen. It reacts with

chlorine at 200°C to form gold(III)

chloride. It forms a number of com-

plexes with gold in the +1 and +3 ox-

idation states.

A

• Information from the WebElements site

Goldschmidt process A method

of extracting metals by reducing the

oxide with aluminium powder, e.g.

Cr 2 O 3 + 2Al →2Cr + Al 2 O 3

The reaction can also be used to pro-

duce molten iron (see thermite). It

was discovered by the German

chemist Hans Goldschmidt

(1861–1923).

Gooch crucibleA porcelain dish

with a perforated base over which a

layer of asbestos is placed, used for

Ültration in gravimetric analysis. It is

glycosidic link 250

g

CH 2 OH CH 2 OH CH 2 OH CH 2 OH

O

OH

OH C1

OH

OH OH

C4 OH

OH

OH

O

OH

OH

OH

condensation O H

C1

O

H

C4 OH

OH

OH

O

+ H 2 O

1–4α-glycosidic

bond

glucose glucose maltose water

Glycosidic bond