Chaim Weizmann, a Russian immigrant living in England came up with a process of making propanone from bacterial fermentation of the starch in maize, bacteria break down the starch in the maize to produce Propanone and Butanol:
(C6H10O5)n CH3COCH3 + CH3(CH2)2CH2OH
n = refers to number of glucose monomer units.
Shipping maize from the US eventually became too difficult and also the Americans needed it for the war effort, to feed soldiers and the public. A replacement was needed, Weizmann was requested to modify his technique to use conkers instead as the supply of conkers was steady and abundant.
Shells that contain the propellant cordite
Over the centuries chemical compounds used in explosives have changed dramatically, with each new development providing an advantage over it’s predecessor.
The earliest known explosive was potassium nitrate (KNO3) this was mixed with sulphur and charcoal. The black powder, as it was known, was the main propellant in military artillery and weapons from the 14th to 19th century. The problem with black powder was the fact masses of white smoke were given off when a weapon was discharged, this meant positions were given away or the amount of smoke meant that generals couldn’t see their armies.
The next development was cellulose nitrate, accidentally formed by mixing sulphuric and nitric acid with cellulose:
The fact that cellulose nitrate has it’s own oxygen supply means that it can be triggered by a sudden impact rather than lighting fuse, also this meant that the reaction was faster therefore less smoke was given off.
Nitro-glycerine was a natural by-product of soap making, it differed from nitro cellulose in that instead of being glucose based it was fat based. It is formed by reacting Glycerine with Nitric acid:
C3H5(OH)3 + 3HNO3 C3H5(NO3)3 + 3H2O
Nitro-glycerine was a high explosive; however it was very volatile and could detonate with little reason. Alfred Nobel was the first man to make a safe high explosive by mixing nitro-glycerine with a clay like substance to make a paste, which could be moulded in to shapes. This became known as dynamite; Nobel perfected the formula with different mixtures until it was perfected.
Production of Nitrocellulose
During the Second World War trinitroluene (TNT) was developed unlike nitro-glycerine TNT doesn’t react with metals so it can be used in metal containers to make bombs.
An explosive reaction must take place very quickly, be exothermic and as many of the products formed must be gasses. Low explosives explode rapidly, these include smokeless powders. Reactions with High explosives take place much faster than low explosives, give out more heat and have higher increases in pressure:
C3H5N3O9(l) 3CO2(g) + 2.5H2O(g) + 1.5N2(g) + 0.25O2(g)
1 mole of liquid 7.25 moles of gas
Pressure is increased because there are more molecules in the same area, the expansion of the hot gasses created cause an explosion so the more hot gasses created by a reaction the bigger the explosion. High explosives manage to create more hot gasses in a quicker time, this means they are more explosive than Low explosives. High explosives react faster as they have more oxygen present in the reaction so oxygen doesn’t have to be used from the air surrounding.
A molecule of TNT an example of a high explosive.
Comparisons between a high and low explosive:
During the mid 1800s the Italian scientist, Sobero was experimenting with nitroglycerine. In his experiments Sobero tasted the substance to see if it was dangerous. Apart from a little nausea he was fine, however this was not very safe as nitro-glycerine could have also quite easily have killed him.
When Nobel was experimenting with nitro-glycerine there was an explosion at his factory killing some chemists, after that the Swedish government prohibited the manufacture of nitro-glycerine near homes. Nobel was to carry out all his experiments on a barge in the middle of a lake.
Sources
- Box 1: Why does gunpowder explode?
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Cordite from Conkers – “Conkering Cordite” by Wilson Flood, Chemistry Review, Volume 10, Number 2, November 2000
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information on making cordite. information on making cordite
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information on nitrocellulose
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information on high an low explosives
- Box 2: Cellulose Nitrate
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“The Big Bang – a History of Explosives” by GI Brown, which appeared in chemistry review, Volume 9, Number 4, November 1999.
- The chemistry of explosives pg 11 – Table of comparisons for high and low explosives.
Picture sources
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- Shells that contain cordite.
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- TNT molecule.