Manufacturing Acetylene (with a Twist of Lime!)
A raw lump of calcium carbide is a grey, slightly metallic looking object. It smells like ozone, stale air from and old tire plus sulfur. Ozone is the smell of electricity in air: the smell of slot cars and toy electric trains.
These combinations of weird smells add up to something familiar, but I couldn't remember what-until I looked at the chemical reaction notation. Then I had a "Proust Moment", only with lime and not lemon cookies. I just had this memory of the smell and seeing my fingers caked with acidic sludge. More on that later.
As you can see in the video, it will not catch fire when a flame is held to it. Once I add water with a syringe it produces Acetylene gas which does ignite. Acetylene burns so well it's used in welding torches!
Calcium carbide is CaC2, written on my sample as CaCa.
Water is H2O.
CaC2 + 2H2O = C2H2 + CA(OH)2
C2H2 is Acetylene, the gas shown burning in the video.
CA(OH)2 is a grey, sludge that smells a bit like... Plaster of Paris!
Back as an undergrad I took a sculpting class. After carving a huge limestone rock I polished it with wet sandpaper and water. The result was this same stinky sludge called slaked lime. Plaster of Paris uses gypsum, while fancier lime plaster uses slaked lime. They smell pretty similar, though lime plaster will burn your skin (as I found out while sanding my sculpture). I remember my fingers burning and that smell of slaked lime, just like Proust was inspired to write 2000 pages after he smelled a lemon Madeline cookie.
Meow-that's funny. I have a Proust Memory Moment every time I smell ferns...of people yelling at me to not kill ferns. I don't listen though.
Strangely enough, I was texturing my hallway ceiling and BOOM there was that smell again! Turns out that the stuff I was glopping on had carbide in its ingredient list.
Placing a lump of calcium carbide into a container and dripping water into it is how old miner's helmets worked (but never do this: read below). A pipe/nozzle system allowed the acetylene gas to rise out of the water and lime sludge: this way the flame doesn't sputter like in the video.
However: miner's helmets are precision instruments with small valves. You may think, "what of he put the lid on that container with the water and calcium carbide and then poked a little hole in the top and lit it?" NEVER, EVER do that!!! I guarantee that it will instantly explode, sending pieces of the container shredding through the room!
Acetylene welding torches often pop while people are using them. It's scary and can blow through your weld-but that flame is out in the open. Contain acetylene (even just a bit, like a bowl with turned inward edges) and you get a bomb with shrapnel! People put acetylene in paper cups laying sideways and ignite them: loud bang, perforated eardrums and wads of paper embedded in your eyeball. It will be the loudest (and last) thing you'll ever hear.
Just laying a piece of paper over the container is enough to make the acetylene explode instead of burn.
If you fill a container with acetylene past 29psi it can explode all by itself-no flame needed! To be able to put acetylene into welding tanks they have to dissolve it into acetone. That lets it get up to 250psi, so it will squirt out of the tank/hose/nozzle while welding-instead of just exploding the tank.
Acetylene in contact with brass or copper forms even more dangerously explosive compounds!
Acetylene is the scariest, most unstable thing I've ever been around...and that's coming from someone who's experimented with neutron radiation.
Leave it alone.
So, besides antique mining helmet lights and ceiling plaster what is calcium carbide and the acetylene it produces good for? Something insanely high tech: thiol vinylation reactions which bind molecules of things like fluorescent markers to biomolecular material being studied. I love fluorescent and phosphorescent stuff!
Kind of like: the glow in the dark fluorescent stuff "clicks" onto the cancer cells. This is called "click chemistry". Thiol bind with acetylene using these methods. Click chemistry focuses (somewhat) on creating reactions that mimic nature, are modular (click together) and are one pot reaction: tons of glassware and tubes and stuff looks cool, but scientists would rather through a bunch of stuff in a bucket and get to work, not spend time synthesising things with a gillion steps.
Another cool thing the carbide and water reaction is good for? Polymers! Search around and you'll find my older posts about polymer. See: everything comes full circle over and over again for me.
