Dictionary of Chemistry [6th Ed.]

vitamin E 550

v

in mature animals. Both conditions

are characterized by weak deformed

bones.

A

• Information about IUPAC nomenclature

vitamin E (tocopherol) A fat-soluble

vitamin consisting of several closely

related compounds, deÜciency of

which leads to a range of disorders in

different species, including muscular

dystrophy, liver damage, and infertil-

ity. Good sources are cereal grains

and green vegetables. Vitamin E pre-

vents the oxidation of unsaturated

fatty acids in cell membranes, so

maintaining their structure.

A

• Information about IUPAC nomenclature

vitamin KA fat-soluble vitamin

consisting of several related com-

pounds that act as coenzymes in the

synthesis of several proteins neces-

sary for blood clotting. DeÜciency of

vitamin K, which leads to extensive

bleeding, is rare because a form of

the vitamin is manufactured by in-

testinal bacteria. Green vegetables

and egg yolk are good sources.

vitreous Having a glasslike appear-

ance or structure.

voltSymbol V. The SI unit of elec-

tric potential, potential difference, or

e.m.f. deÜned as the difference of po-

tential between two points on a con-

ductor carrying a constant current of

one ampere when the power dissi-

pated between the points is one watt.

It is named after Alessandro Volta.

Volta, Alessandro Giuseppe An-

tonio Anastasio(1745–1827) Ital-

ian physicist. In 1774 he began

teaching in Como and in that year in-

vented the electrophorus. He moved

to Pavia University in 1778. In 1800

he made the *voltaic cell, thus pro-

viding theÜrst practical source of

electric current. The SI unit of poten-

tial difference is named after him.

voltaic cell (galvanic cell)A device

that produces an e.m.f. as a result of

chemical reactions that take place

within it. These reactions occur at

the surfaces of two electrodes, each

of which dips into an electrolyte. The

Ürst voltaic cell, devised by Alessan-

dro Volta, had electrodes of two dif-

ferent metals dipping into brine. See

primary cell; secondary cell.

voltaic pileAn early form of bat-

tery, devised by Alessandro Volta,

consisting of a number ofÛat

*voltaic cells joined in series. The liq-

uid electrolyte was absorbed into

paper or leather discs.

voltameter(coulometer)1.An

electrolytic cell formerly used to

measure quantity of electric charge.

The increase in mass (m) of the cath-

ode of the cell as a result of the depo-

sition on it of a metal from a solution

of its salt enables the charge (Q) to be

determined from the relationship Q =

m/z, where z is the electrochemical

O CH 3

CH 3

OH

3 CH

CH 3

CH 3

CH 3 CH 3 CH 3

Vitamin E