Post by Gill Smithsulphur + carbon + potassium nitrate
why sulphur AND carbon?
the purpose of either is to burn and vaporise using oxygen from the
nitrate in an autocatalytic reaction
dramatically increasing pressure
kerrrrrBOOM
but, why both?
The sulphur is there to get the gunpowder to ignite at lower
temperatures. After percussion caps were invented, someone tried
gunpowder without sulphur and found it worked fine, in fact you didn't
have the smoke that you got from the old formula.
http://en.wikipedia.org/wiki/Gunpowder#Sulfur-free_gunpowder
Sulfur-free gunpowder
The development of smokeless powders, such as cordite, in the late 19th
century created the need for a spark-sensitive priming charge, such as
gunpowder. However, the sulfur content of traditional gunpowders caused
corrosion problems with Cordite Mk I and this led to the introduction of
a range of sulfur-free gunpowders, of varying grain sizes.[51] They
typically contain 70.5 parts of saltpetre and 29.5 parts of charcoal.[51]
Like black powder, they were produced in different grain sizes. In United
Kingdom, the finest grain was known as sulfur-free mealed powder (SMP).
Coarser grains were numbered as sulfur-free gunpowder (SFG n): 'SFG 12',
'SFG 20', 'SFG 40' and 'SFG 90', for example; where the number represents
the smallest BSS sieve mesh size on which no grains were retained.
The main purpose of sulfur in gunpowder is to decrease the ignition
temperature. A sample reaction for sulfur-free gunpowder would be
6 KNO3 + C7H8O ? 3 K2CO3 + 4 CO2 + 2 H2O + 3 N2