Dictionary of Chemistry [6th Ed.]

Ürst of a class of similar complexes

called *sandwich compounds. Its sys-

tematic name is di-π-cyclopentadi-

enyl iron(II).

ferrocyanide A compound con-

taining the complex ion [Fe(CN) 6 ]4–,

i.e. the hexacyanoferrate(II) ion.

ferroelectric materials Ceramic

dielectrics, such as Rochelle salt and

barium titanate, that have a domain

structure making them analogous to

ferromagnetic materials. They ex-

hibit hysteresis and usually the

piezoelectric effect.

ferromagnetism See magnetism.

ferrosoferric oxide See triiron

tetroxide.

ferrous compounds Compounds

of iron in its +2 oxidation state; e.g.

ferrous chloride is iron(II) chloride,

FeCl 2.

fertilizerAny substance that is

added to soil in order to increase its

productivity. Fertilizers can be of nat-

ural origin, such as composts, or they

can be made up of synthetic chemi-

cals, particularly nitrates and phos-

phates. Synthetic fertilizers can

increase crop yields dramatically, but

when leached from the soil by rain,

which runs into lakes, they also in-

crease the process of eutrophication.

Bacteria that canÜx nitrogen are

sometimes added to the soil to in-

crease its fertility; for example, in

tropical countries the cyanobac-

terium Anabaena is added to rice pad-

dies to increase soil fertility.

Übrous protein See protein.

Fick’s law A law describing the dif-

fusion that occurs when solutions of

different concentrations come into

contact, with molecules moving from

regions of higher concentration to re-

gions of lower concentration. Fick’s

law states that the rate of diffusion

dn/dt, called the diffusive fluxand de-

noted J, across an area A is given by:

dn/dt = J = –DA∂c/∂x, where D is a con-

stant called the diffusion constant,

∂c/∂x is the concentration gradient of

the solute, and dn/dt is the amount of

solute crossing the area A per unit

time. D is constant for a speciÜc

solute and solvent at a speciÜc tem-

perature. Fick’s law was formulated

by the German physiologist Adolf

Eugen Fick (1829–1901) in 1855.

Üeld effect See electronic

effects.

Üeld-emission microscope (FEM)

A type of electron microscope in

ferrocyanide 224

f

metal

tip

liquid

helium

electronselectronselectrons

to vacuum

pump

fluorescent

screen

high

negative

voltage

Field-emission microscope