tute for Heavy Ion Research where it
wasÜrst produced.
A- Information from the WebElements site
date-rape drugsDrugs that are
used to render the victim unable to
resist a sexual assault. Particular
drugs used for this purpose areÛuni-
trazepam and gammahydroxybutyric
acid (GHB).
dating techniquesMethods of es-
timating the age of rocks, palaeonto-
logical specimens, archaeological
sites, etc. Relative dating techniques
date specimens in relation to one an-
other; for example, stratigraphy is
used to establish the succession of
fossils. Absolute(or chronometric)
techniquesgive an absolute estimate
of the age and fall into two main
groups. TheÜrst depends on the exis-
tence of something that develops at a
seasonally varying rate, as in den-
drochronology and varve dating. The
other uses some measurable change
that occurs at a known rate, as in
*chemical dating, radioactive(or ra-
diometric) dating(see carbon dating;
fission-track dating; potassium–
argon dating; rubidium–strontium
dating; uranium–lead dating),
*amino acid racemization, and *ther-
moluminescence.dative bondSee chemical bond.
daughter1.A nuclide produced by
radioactive *decay of some other nu-
clide (the parent). 2.An ion or free
radical produced by dissociation or
reaction of a parent ion or radical.
Davisson–Germer experiment
See electron diffraction.
Davy, Sir Humphry (1778–1829)
British chemist, who studied gases at
the Pneumatic Institute in Bristol,
where he discovered the anaesthetic
properties of *dinitrogen oxide (ni-
trous oxide). He moved to the RoyalInstitution, London, in 1801 andÜve
years later isolated potassium and
sodium by electrolysis. He also pre-
pared barium, boron, calcium, and
strontium as well as proving that
chlorine and iodine are elements. In
1816 he invented the *Davy lamp.
Davy lampAn oil-burning miner’s
safety lamp invented by Sir Humphry
Davy in 1816 when investigating
Üredamp (methane) explosions in
coal mines. The lamp has a metal
gauze surrounding theÛame, which
cools the hot gases by conduction
and prevents ignition of gas outside
the gauze. IfÜredamp is present it
burns within the gauze cage, and
lamps of this type are still used for
testing for gas.d-block elementsThe block of el-
ements in the *periodic table consist-
ing of scandium, yttrium, and
lanthanum together with the three
periods of transition elements: tita-
nium to zinc, zirconium to cadmium,
and hafnium to mercury. These el-
ements all have two outer s-electrons
and have d-electrons in their penulti-
mate shell; i.e. an outer electron
conÜguration of the form (n–1)dxns^2 ,
where x is 1 to 10. See also transition
elements.DDTDichlorodiphenyltrichloro-
ethane; a colourless organic crys-
talline compound, (ClC 6 H 4 ) 2 CH(CCl 3 ),
made by the reaction of trichloro-
methanal with chlorobenzene. DDT
is the best known of a number of
chlorine-containing *pesticides used
extensively in agriculture in the
1940s and 1950s. The compound is
stable, accumulates in the soil, and
concentrates in fatty tissue, reaching
dangerous levels in carnivores high
in the food chain. Restrictions are
now placed on the use of DDT and
similar pesticides.deacetylationThe removal of andate-rape drugs 162d