divided by an arbitrary extensive
variable, such as the volume, an *in-
tensive variable results. A macro-
scopic system can be described by
one extensive variable and a set of in-
tensive variables.
external conversion A process in
which molecules in electronically ex-
cited states pass to a lower electronic
state (which is frequently the ground
state) by colliding with other mol-
ecules. In this process the electronic217 external conversion
e
EXPLOSIVES
900–1000 Gunpowder developed in China.
1242 English monk Roger Bacon (1220–92) describes the preparation of
gunpowder.
c.1250 German alchemist Berthold Schwarz claims to have reinvented
gunpowder.
1771 French chemist Pierre Woulfe discovers picric acid (originally used as a
yellow dye).
1807 Scottish cleric Alexander Forsyth (1767–1843) discovers mercury
fulminate.
1833 French chemist Henri Braconnot (1781–1855) nitrates starch, making a
highly flammable compound (crude nitrocellulose).
1838 French chemist Théophile Pelouze (1807–67) nitrates paper, making
crude nitrocellulose.
1845 German chemist Christian Schönbein (1799–1868) nitrates cotton,
making nitrocellulose.
1846 Italian chemist Ascania Sobrero (1812–88) discovers nitroglycerine.
1863 Swedish chemist J. Wilbrand discovers trinitrotoluene (TNT).
Swedish chemist Alfred Nobel (1833–96) invents a detonating cap
based on mercury fulminate.
1867 Alfred Nobel invents dynamite by mixing nitroglycerine and kieselguhr.
1871 German chemist Hermann Sprengel shows that picric acid can be used
as an explosive.
1875 Alfred Nobel invents blasting gelatin (nitroglycerine mixed with
nitrocellulose).
1885 French chemist Eugène Turpin discovers ammonium picrate (Mélinite).
1888 Alfred Nobel invents a propellant from nitroglycerine and nitrocellulose
(Ballistite).
1889 British scientists Frederick Abel (1826–1902) and James Dewar invent a
propellant (Cordite) similar to Ballistite.
1891 German chemist Bernhard Tollens (1841–1918) discovers pentaerythritol
tetranitrate (PETN).
1899 Henning discovers cyclotrimethylenetrinitramine (RDX or cyclonite).
1905 US army officer B. W. Dunn (1860–1936) invents ammonium picrate
explosive (Dunnite).
1915 British scientists invent amatol (TNT + ammonium nitrate).
1955 US scientists develop ammonium nitrate–fuel oil mixtures (ANFO) as
industrial explosives.