For technical reasons, it turns out that alkali metal atoms are particularly good candidates for laser cooling. Rubidium is probably the most favorable of all of them– some atomic physicists jokingly refer to it as “God’s atom”– but all of the alkalis, even Francium, have been cooled and trapped.
Of course, alkali metal elements are also the ones that explode when they come in contact with water. They’re insanely reactive, so you have to be very careful handling them. As a result, they’re usually shipped either in vacuum-sealed ampoules, or as chunks of metal packed in some oily liquid, to keep them from reacting with the water vapor in the air.
This combination means that pretty much anyone who has ever done a laser cooling experiment has some True Lab Stories about alkali metal mishaps. My personal story isn’t all that impressive (as an undergrad cleaning out a vacuum system that had been used with Rb, I was advised to use ethanol rather than water on the first pass, because it reacts more slowly. Of course, it’s also flammable, so when we filled the arm of the chamber that had held the 5-g slug of rubidium metal with ethanol, we got a cheery little blaze…), but there was an impressive incident in the lab when I was in grad school, that I’ll relate after the cut…
The lab I worked in had several different experiments going. I was working with noble gases (specifically xenon), which are famously inert, but we had a cesium experiment, plus two sodium experiments.
One of the sodium experiments had some sort of design flaw that caused it to run through a hellacious amount of sodium in a short period of time, which meant the source needed to be re-filled on a regular basis. This was kind of a headache, since it involved opening the vacuum system up, removing the oven (sodium needs to be heated to a few hundred degrees to get a reasonable amount of vapor), adding more sodium, closing everything back up, and pumping the system back down. The pump-down takes a few hours, so they tended to do the re-filling at the end of the day (so they could turn the pumps on, go home, and come back in the morning to find everything ready to go).
On one occasion, the re-fill was done rather late at night, by a post-doc working alone. He got everything closed back up, and started the pumps, and then set about cleaning up. He put the leftover sodium back in the jar (this particular batch was bought as chunks of metal packed in xylene, an oily liquid sort of like kerosene, only less flammable), put the jar and the various other tools in a metal tray, and headed back for the hood room where we kept the alkali metals.
To get from the lab out into the hallway, you had to pass through the computer room/ break room, and open two doors, one from the lab into the break room, and one into the hall. He made it into the break room with no trouble, but when he went to open the door into the hall, he had to balance the tray on the edge of a sink to free up a hand. And you can see where this is going…
In accordance with Murphy’s Law, the tray tipped over into the sink, which was one of those institutional granite sinks that are more or less impervious to anything you might manage to dump into them, but always have about a quarter-inch of standing water somewhere in the bottom. And, of course, the jar fell out of the tray, and shattered, dumping the sodium directly into the water.
Describing it the next day, he said that he saw the metal skid into the water, and small flames start up, and thought “This is bad…” Then, the xylene went up, in a fireball that reached the ceiling.
Amazingly, he kept a cool head, and went to get the Met-L-X. You can’t put out alkali fires with regular fire extinguishers, so you need to sort of smother them in anhydrous soda ash, which we had on hand. He got the stuff, and got the fire put out without any significant damage.
At this point, he was hugely relieved to not hear loud fire alarms going off, but figured that just to be safe, he should call the Fire Safety office, and tell them what happened. He dialed the emergency number, and the person who picked up the phone said “We were wondering whether you were going to call. The fire crew should be there, well, now.” And when he looked out in the hall, there were fire fighters sprinting down the hall toward him…
It seems they have a silent alarm on the fire sensors in the labs, so they don’t wind up panicking the entire building every time some clumsy chemist makes a little smoke. They need to get alarms in multiple labs (or a phone call) before the big sirens start up, but they will send a crew for a single alarm, especially after hours.
The post-doc in question got in a whole bunch of trouble for that, and we had to agree that nobody would ever re-load the alkali metal sources after hours, but other than that, everything was ok. That wasn’t the worst interaction the group ever had with Fire Safety, though, but that’s a story for another time…
I love stories like this. My favorite Murphy’s Law story came at the college I first went to where some idiot put some sodium in his pocket. Of course he was a tad sweaty and . . .
Next up, but with no apparent consequences to his later children that I can see, was the guy who put the Einsteinium in his pocket. Near the family jewels.
The number one Murphy Law case was down at Los Alamos where some engineers were trying to figure out why a laser wasn’t firing right. This was one of those lasers that were enclosed in huge buildings. They were very big with very large arrays of capacitors. Even though the capacitors were discharged you still need to be careful. This guy, figuring out the problem, runs in the room and points “the problem is here…” But of course pointing when there is lots of electricity around isn’t wise. A huge discharge comes off the capacitors, blows out his teeth, solidified his eyes, stopped his heart, and nearly killed the guy. They still talk about it when preparing you for safety classes while working on lasers there.
I feel bad for that guy, because I’m sure his life was a mess after that. But all the stories I hear about lab work makes me glad I don’t work in labs anymore.
Why’d the guy get in such trouble? Sure, he did something dumb, but he handled it admirably and — very important point — honestly. It’s a safe bet he knows full well that he screwed up. Ream this guy out, and the next person to screw up — oh yes, there will be a next person, a next screwup — is going to have more incentive to cover up than to cooperate. Safety depts shoot themselves in the feet sometimes when they focus more on punishing breaches than on rewarding good behaviour.
Blimey. Lithium fires need a special fire extinguisher? This I did not know.
He got in trouble mostly because the lab safety policy said that in the event of a fire, you were to leave the lab, and call it in from somewhere else. It was a violation of the safety policy to go get the Met-L-X and put the fire out himself.
They let him off with a stern lecture and a promise from the group that nobody would ever do that again, mostly because he did get the fire out without causing any further damage, and because the fire crew would’ve had to ask him where the Met-L-X was kept anyway…
Well, at least the fire brigade didn’t hose down the scene of the crime with water ;-).
An urban legend (unverified, ’50s, ’60s) from Amsterdam goes as follows:
Over the year the chemistry faculty lab of the University of Amsterdam used to collect the sodium left-overs from practice in a big jar with petrolium. At the end of a fourth semester two students were (as usual) dispatched with the jar and two large pincers to the moat running along the lab building. Their job was to dump the sodium scraps into the water one at the time, and let nature reclaim the sodium.
At first this was fun of course, watching the sodium perform all kinds of different stunts on the water, depending on scrap size. But after some time the students started to realise that they were going to be there for the best part of the day, dumping sodium at the rate they were instructed to maintain. By that time the thrill was gone and they decided to turn over the jar and dump its contents into the moat in one go.
Allegedly a blast resulted that took out a few parked cars and a lot of chemistry lab windows. The story doesn’t recount the students’ fate……
I got this story from my brother-in-law, who studied chemistry at that faculty in the ’60s, but it happened before his time.
Lithium is pretty mellow. It is in lithium batteries and will just bubble if you dump it into water.
Potassium is much worse than sodium (in terms of self-ignition on moist air) and rubidium, cesium, sodium+potassium (room-temp-liquid alloy) are very nasty indeed.
There was a funny incident with an irrate father liquidating a home lab (after his son tried to produce ethyl mercaptan and succeeded). He started dumping jars with chemicals into a lavatory. When he dumped a jar of sodium with mineral oil into WC, the thing caught fire so dad quickly flushed. The sodium exploded one floor below. This happened in a highrise appartment building; the content of the waste pipe emptied into the bathroom of their poor neighbours after explosion.
Mmmm…violent exothermic reactions. My favorite. I wasn’t allowed to work alone in the chemlab in high school once I’d gotten an understanding of how things worked. It’s still tempting to go back and finish my degree in chemistry just so I can play in a lab again.
What?
I’ve used sodium in lab demos. Cut off a cc’s worth with a butter knife in front of students. Drop it into a nalgene half full of water, listen to the pop and sizzle, and if all goes well, a flash of light and a little mushroom cloud. The kids of course want larger chunks dropped in … Do it again!
At my school in South Africa, we had a fish pond in front of the school . I did not witness the event, but the story goes that the kids persuaded their chem teacher to drop a large chunk of sodium into the fish pond. Not sure how large the chunk was, but the turmoil in the pond, the resulting explosion and the flying fish made for a memorable experience.
The post-doc also violated one important lab safety rule: never work alone. It’s better to bribe someone with food or beer to stick around and help, then risk bodily harm.
I meant to say a “nalgene graduate.”
Bah. Elements.
Phenol distillation, now.
Or the proverbial empty ether bottle, left sitting in the back of the fume hood.
Or the bottle of picric acid I found one afternoon, doing my assigned cleanout of a disused 1960s laboratory when we were moving to a new building….
Sodium? Well, that’s common as dirt, innit?
Brings to mind Theodore Gray’s Sodium Party videos.
Their job was to dump the sodium scraps into the water one at the time, and let nature reclaim the sodium.
At first this was fun of course, watching the sodium perform all kinds of different stunts on the water, depending on scrap size. But after some time the students started to realise that they were going to be there for the best part of the day, dumping sodium at the rate they were instructed to maintain.