Untitled Document

21 November 2003

E-Bulletin Backscatter

Make Your Own Chemicals

Sheldon,

Norm Stanley's "Make Your Own Chemicals" articles inspired me to try something that I had read about on the internet a few months ago. While searching for something else I ran across a description of Thomas Wilson's discovery of a way to make calcium carbide. Thomas was actually trying to make calcium by using carbon to extract the oxygen from calcium oxide.

Calcium carbide when combined with water produces acetylene. This accidental discovery created a whole new industry. What Wilson did was to combine calcium oxide (lime) and carbon and heat it with an electric arc furnace.

Since I have most of the supplies and equipment to do this experiment, I thought it would fun to try and make some calcium carbide. The only thing that I was missing was some lime. So I went to the garden supply store to buy some. Turns out that garden supplies are seasonal and most of the stores stock had been converted to selling Christmas decorations. Finally I found a bag of lime in the back room of the store. Reading the contents of the bag I found out that the lime they sell is not pure. It is only 50% calcium hydroxide (slaked lime) the rest is magnesium hydroxide. Oh well it will probably still work. I suppose I could have just ground up some of the limestone gravel in my drive.

The temperature in an arc furnace is so high that almost nothing can survive so I will use a method where the material I am heating is its own container. So now we have some lime and some old charcoal for the carbon. My trusty welder, a couple of carbon arc electrodes and a terra cotta flower pot complete the needed supplies. I drilled two holes in the side of the flower pot for the carbon arc electrodes and filled the pot with a mixture of lime and crushed charcoal. By sticking the electrodes into the holes in the pot they can be made to meet in the middle of the contents. I connected the electrodes to the welder and set the current to 105 Amps. When I struck an arc in the middle of the lime the gasses given off made a small plume of lime and carbon coming out of the pot. BTW This is definitely an outdoor project. The lime dust got all over everything. Small orange flames shot out of the holes around the electrodes and finally a flame broke thru and came out of the top of the pot. After running the arc for a minute or so I shut things down and let it cool. After it had cooled down somewhat I dumped the contents of the pot. Besides the unused lime mixture there was a black egg shaped lump around the electrodes. I broke this up and separated it from the rest of the material. If the black material is calcium carbide it should fizz and give off acetylene when put in water. So I put a piece of it into a dish with water. Sure enough it starting bubbling and the gas would light with a match. Since you can still buy calcium carbide in the US, with only the HAZMAT shipping charges making things expensive, this process is not worth it just to get some carbide but it was fun seeing how it works.

Jim Hannon

Bouncing Ball Analog Computer

Dear Sheldon;

It came to my attention that the 2N4870 transistor Q2, in my analog bouncing ball computer has become obsolete but you can still get it at NEWARK ELECTRONICS 1-800-463-9275 or 4801 North Ravenswood, Chicago, IL 60640. The part number is 35CO717. When calling, ask for this number.

Craig Kendrick Sellen