Open Eye: Gunpowder, treason and plot...

WHEN King George I sailed gracefully down the Thames in his Royal Barge in July 1717 it was to the accompaniment of a spectacular display of pyrotechnics and a new orchestral piece by Mr Handel: Music for the Royal Fireworks.

He may have reflected that the substance then giving him so much enjoyment very nearly ended the life of one of his predecessors just over a century earlier. Or perhaps such ironies never crossed his mind.

The essential ingredient of all fireworks is essentially the same as that which filled the kegs underneath the Houses of Parliament one fateful day in 1695. It is of course gunpowder.

The plot hatched by Guy Fawkes and his friends depended on a comparatively new method of mass destruction. Less than 50 years had elapsed since the opening of the first gunpowder factories in Britain, though it must have been manufactured on a small scale for some time before.

Britons subsequently claimed its discoverer to be a 13th century Friar from Ilchester, one Roger Bacon (the Germans had an alternative hero), though rumour had it that gunpowder was known to the Chinese or even the ancient Greeks. But kegs of the stuff were certainly not available until the end of the 16th century.

Waltham Abbey had a gunpowder factory in 1570 supplying a government which doubtless found its product useful in dealing with the Spanish Armada. Even earlier (1560) a gunpowder mill could have been found at Chilworth in Surrey, gaining its power from the little River Tillingbourne.

Such a facility was vital, for the constituents of gunpowder need careful mixing, and machinery is much better than working by hand. This greyish black material is not a single chemical compound (like TNT) but rather a carefully blended mixture. It has three components which have to be in the right proportions and extremely well mixed. There are the two chemical elements sulphur and carbon (in the form of charcoal). But the majority component (about 75%) is a substance variously called "nitre", "saltpetre" or just potassium nitrate.

Gunpowder will often burn quite quietly if a match is applied, but on receiving a sharp blow it explodes with devastating force. The carbon and sulphur are oxidised by the oxygen in the saltpetre and form the familiar gases carbon dioxide and sulphur dioxide.

What makes the situation explosive is the rate at which these gases are formed. They appear so quickly that they have no chance to effect a gentle escape. Consequently in a tiny fraction of a second they build up enormous pressure on anything around them and will eject a cannon ball from a gun with immense force.

In a closed room, however, they will wreak devastation by blowing walls and ceiling apart.

When we ask where the constituents come from we discover that some people would do almost anything to get enough to make gunpowder.

First there was sulphur - the element free and uncombined. This does not occur in Britain and had to be imported. Since it is a product of volcanic eruptions mush sulphur was obtained from the slopes of Mount Etna in Sicily. At first it was scraped up from the ground by hand, but as demand rose it had to be mined and almost inexhaustible quantities seemed to be available. By the early 19th century it was also in demand for the manufacture of sulphuric acid, but that is another story.

It is said that when Cortes, the Spanish conqueror of Mexico in the 16th century, desperately wanted gunpowder he took advantage of the neighbouring volcano Popocatapetl. An intrepid lieutenant was lowered into the crater which was freely lined with sulphur deposits.

Saltpetre was imported from Spain and elsewhere until Elizabethan times. As demand increased efforts were made to produce it from native materials. When sewage, slaughter- house residues, chicken droppings and other nasty effluents get together the nitrogen they contain may end up as nitrates. In the neighbourhood of limestone buildings or even in the mortar of brick structures crystals of calcium nitrate could often be observed.

So arose one of the oddest and most unpopular vocations even for those days. Individuals were employed to scrape off the nitrate, with authority to enter private property. It was said that they "dig in all places without distinction, as in parlours, bedchambers, threshing and malting floors, yea God's own house they have not forborne".

In France it was even worse in the Revolutionary war with Britain. The products of the petre-men's labour were converted in to saltpetre by treating with potash. This in its turn was available from the ashes obtained by burning wood. And it was wood that provided the third constituent of gunpowder: charcoal. Like potash, charcoal was a product of the forests that once covered much of southern England.

But by the time gunpowder manufacture became big business many of these forests (as in the Weald) had been largely destroyed, the charcoal being used not for gunpowder but to make the iron ships of Elizabeth's Navy, and the very cannon for which the gunpowder was required.

With the 18th century came a demand for gunpowder for blasting purposes. Powder mills were established in other parts of the country, such as the Lake District and its surrounding countryside. Here there was abundant woodland and plenty of fast-flowing water to power the mills.

Gunpowder was used for military purposes until the Boer War. Now it is entirely replaced by TNT, nitro-cellulose and other synthetic compounds. Black powder is confined to fireworks and sporting guns; it is all imported. Today there are few traces left of the gunpowder industry.

Often there were explosions with devastating consequences for the neighbourhood. Some sites have been taken over by nature, many as caravan sites, or for alternative industries. One has been overrun by a time-share leisure complex, perhaps the most undignified end of all for a once mighty industry.

Professor Colin Russell is Emeritus Professor, and Visiting Research Professor, in the OU History of Science Department.