Incendiary silver – silver acetylide contact explosive

Incendiary silver – silver acetylide contact explosive


In 1866 Marcellin Berthelot was experimenting with acetylene gas in various metal salts including silver nitrate. What he found was that as the gas bubbles through the solution of ammonical silver nitrate a white solid was produced. He noticed that upon drying it became extremely explosive. He called it L’acétylure d’argent – silver acetylide. Pure silver acetylide is an unusual explosive because in principle it produces no gas when it explodes. The bang it produces is almost completely down to the rapid transfer of a lot of heat to the surrounding air which in turn will rapidly expand. To produce it safely in a school environment we have to be careful not to produce double salts which produce gases as well adding to the power of the explosion. So its of the utmost importance that we don’t add the acetylene directly to the silver nitrate and lazily chucking calcium carbide into the solution directly is a bad plan too. To make sure we’re only producing the single salt, a multi-tube set up is used. In the first tube there’s water. Here calcium carbide reacts with water to generate acetylene gas. The gas is then bubbled through copper sulfate solution to remove any hydrogen sulfide impurities and in to a tube containing ammoniacal silver nitrate to form the white precipitate of silver acetylide. Well I say white, it’s sort of white. In the UK without an explosives certificate it’s illegal to generate more than half a gram of any explosive so we’re going to use the concentration of silver nitrate to control the mass of acetylide we can produce. You make up the ammoniacal silver nitrate solution by adding 1 molar solution of sodium hydroxide dropwise to 15 ml of a 0.25 molar silver nitrate solution until the precipitate of silver oxide forms. Add a 2 molar ammonia solution drop-wise stirring thoroughly until the precipitate re-dissolves to form a colorless solution. The filtered solid is stable enough when moist so it can be safely moved to a gauze over a Bunsen for heating. Once it dries out the bangs begin Cleanup can be a pain in the neck because during the reaction bits of acetylide get thrown out, dry, and in a few hours later is detonated as somebody walks past. That’s why some fine gauze like this steel insect screen can be handy for catching strays. Once you’re done, the area around the experiment can be cleaned up by passing over it with a Bunsen flame. If you’re not using the insect screen like I’ve used a large sheet of hardboard is super useful for this purpose so you don’t wreck your table surfaces when you pass a Bunsen over them. You can find further information and technician sheets to support this demonstration on the all-new Education in Chemistry website. So head over there and check it out.

5 Comments

  1. In the UK you don't even have freedom of speech, so I am surprised that your betters allow you to produce even 1/2g of explosive.

Leave a Reply

Your email address will not be published.


*