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Sublimation works either way, solid to gas or gas to solid, according to AHD anyway. The important point is that the liquid phase is bypassed.
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Dear Faldage: It would be nice of AHD had cited system in which gas goes directly to solid.
I'm prepared to believe it can happen, but I have never seen icicles grow.
Another example of sublimation that I remember involves crystals of iodine. I used to take
tincture of iodine, and add strong ammonia to it. Purple crystals of NI3 are fprmed. They
can be collected on a filter paper. They are harmless when wet, but when dry are violently
explosive. Trick was to spread wet crystals on floor. A few hours later anybody who stepped
on them got an alarming surprise. Janitor sweeping floor would get shell-shocked. The French
chemist who discovered the reaction lost a couple fingers learning about handling the product.
Would you call that a sublime explosion? Iodine crystals also sublimate slowly.
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It would be nice of AHD had cited system in which gas goes directly to solid.
It's a dictionary, Dr. Bill, not a physics textbook.
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Dear Faldage: amazing what can be found on Internet! I searched for "NI3" and got
a ten year old post by a guy who as a High School freshman made iodine from an old
chemistry book experiment adding KI to sulfuric acide. It gave off gaseous iodine, which
he collected on an ice filled Petri ;dish. That would be reversed sublimation. He then
made NI3, in an aluminum dish. It ate through the dish onto floor. He says he got a
surprise when he went into his (fortunately) isolated chemistry shack the next day.
I'll bet he did.
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Gas goes directly to a solid when you compress and cool carbon dioxide. Just as the solid goes directly to a gas when you expose "dry ice" at room temperature. In the back of my mind is a recollecton that the liquid state of CO2 is only when one very particular temperature and pressure point is established, and it has to be within a tenth of a degree and a couple millibars of pressure.
TEd
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Dear TEd: you bring back memories of my youth, seeing pharmacist make dry ice for
my father to use for removing warts. The pharmacist had a cylinder of the gas,
and put a piece of chamois leather over the nozzle, then when knob was turned,
the gas that escaped through the chamois removed enough heat from the gas
inside the chamois that solid CO2 was formed.
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Well, that's not exactly the physics, Bill. All the chamois did was serve as a container for the dry ice.
I have a CO2 extinguisher, filled with highly compressed CO2. When I open the valve, the CO2 comes out and expands rapidly (hark back to our discussion about air conditioning some months ago.) There is only a certain amount of ambient energy in the gas (it was at room temperature under great pressure.) It expands and gets really REALLY cold (a couple hundred degrees below zero. The gas sublimates into a solid (dry ice) and begins to evaporate furiously.
The chamois contains the crystals of dry ice and insulates it a bit so the evaporation is controlled a little bit. What makes it feel cold is the rapid evaporation that's taking place.
TEd
TEd
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Dear TEd: I had physics so long ago I am not equipped to debate the matter. But if
you just turned the nozzle, you would get only a few bits of solid. The chamois does
promote the production of the dry ice. Speaking of CO2 fire extinguishers, when I
was asst. director at Biological Lab, a safety inspector found all our CO2 extinguishers
empty. It took a bit of detective work to discover that a night watchman who had been
told to kill any mice that had escaped from cages had done so by turning CO2
fire extinguishers on them.
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And did he yell "Freeze" at the poor miceys before he shot them, I wonder?
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Dear Consuelo: I did a bit of freezing when my secretary got upset by finding a bat
in her office. I didn't want to hurt it, so I got a spray vial of ethyl chloride, which
used to be used to reduce pain from needles (not very effectively) and sprayed
the bat just enough to make him drop into a basin held under him. I think maybe
it acted as inhalation anaesthetic. But I took him outdoors, and in a few minutes
he flew off.
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