Science Interviews

Interview

Sun, 12th Jul 2009

This week in science history - The first demonstration of dynamite

Sarah Castor-Perry

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This week in science history saw, in 1867, Alfred Nobel first demonstrate dynamite in the UK, at Merstham Quarry in Surrey. Nobel had invented dynamite two years earlier and this demonstration was the first step towards a lucrative UK patent for the substance.

Alfred nobelMost people would recognise the name Alfred Nobel from the prestigious Nobel Prizes, but his work on dynamite and later forms of explosives was what allowed him to build up the huge fortune that he left in his will to set the Nobel Prizes up. There are 5 prizes, first awarded in 1901 and which have been awarded annually, except for three years during the second World War, for eminence in Chemistry, Physics, Medicine or Physiology, literature and rendering services to international fraternity and peace-keeping.

Before Nobel’s work, the main explosives in use were gunpowder and nitroglycerine.

Gunpowder was discovered by Taoist monks in China in the 9th Century AD and is a mixture of sulphur, charcoal and potassium nitrate. It was used as a propellant for firearm weapons – rifles, pistols and cannons etc, and also as an explosive for mining and tunnel excavation (or to try and blow up a building, such as in the 1605 Gunpowder Plot to blow up the Houses of Parliament).

The main difference between gunpowder and dynamite is that gunpowder ‘deflagrates’, whereas dynamite (and other modern forms of explosive) ‘detonate’. This basically means that gunpowder (a low explosive) burns, and dynamite (a high explosive) explodes – gunpowder will produce enough force to push a bullet out of the barrel of a gun, but not enough to explode the gun barrel itself.

Nitroglycerine was first synthesised in Italy in 1847 by nitrating glycerol. It was seen as a usable (and much more powerful) alternative to gunpowder. However, it is extremely dangerous – it is highly shock sensitive, meaning a physical shock will cause it to explode. Alfred Nobel’s own brother Emil was killed in a Nitroglycerine factory explosion, and this was one of the factors that made him set about finding a way to make the transport and use of Nitroglycerine safer, whilst maintaining its powerful explosive properties.

Dynamite

A. Sawdust (or any other type of absorbent material) soaked in nitroglycerin.

B. Protective coating surrounding the explosive material.

C. Blasting cap.

D. Electrical cable connected to the blasting cap.

Nobel discovered that mixing nitroglycerine with an absorbent substance like diatomaceous earth (a sort of sedimentary sand) or sawdust and a small amount of sodium carbonate made it much more stable and safe to transport, but still delivered the high explosive power of the nitroglycerine compared to gunpowder. The mixture was formed into sticks and wrapped in paper – an image well known to anyone who has seen a spaghetti western film. It requires a small explosion from a ‘blasting cap’ to initiate the explosion of the dynamite. Nobel used a pyrotechnic one using flammable chemicals, but modern blasting caps may also set off explosions using electric charges. Originally, Nobel marketed dynamite as ‘Nobel’s Blasting Powder’ and over the next few decades, he expanded his operations, and with his patents in several countries and shares in most dynamite-or-similar producing companies, he grew extremely wealt

Later developments that Nobel made included gelignite or blasting gelatine, that he invented in 1875 – made by dissolving nitrocellulose (itself highly explosive) in nitroglycerine and mixing it with wood pulp and sodium nitrate. This and innovations such as cordite, invented by two Britons, were safer than dynamite in that thy did not have the alarming habit of leaking nitroglycerine when stored for too long, and had more explosive power as the nitrocellulose used to stabilise the nitroglycerine was also a high explosive, unlike the stabilisers in dynamite. Blasting gelatine was widely used in Ireland during the War of Independence and into the 1960s by the IRA, before it was replaced by modern plastic explosives such as semtex.

Dynamite is still in use today, although with slightly different composition to Nobel’s original mixture. Other forms of explosives such as semtex and C4 are also used in demolitions, commercial blasting and for military use.

It is said that the reason Nobel left such a large amount of his fortune to set up the Nobel Prizes is because he wanted a better lasting legacy than the invention of something that although has helped global industry to grow and thrive, also presented a way of killing more people faster than ever before. Given that most people know his name in relation to the Prizes rather than dynamite, and that the Prizes help to recognise and publicise global academic achievement, he seems to have succeeded in his wish.

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