Any reasonable explanation for this?
I was boiling water in a Visions Corningware pyrex pot on a gas stove. When it got to a roiling boil, I dropped in a frozen potsticker (Chinese dumpling) and the pot shattered right on the stove. I had boiled water in the pot before, and I had cooked food in the pot before. There were no visible cracks or nicks in the pot. I realize that there was probably some kind of fracture in the pot, but what puzzles me is this: Was the temperature differential so great (boiling temp and freezing temp meeting at the same moment) that an unusual rate of energy released would cause the pyrex to be more vulnerable to weakness than other instances of heating food?
Glasses expand and contract when their temperature is modified. Suddenly cooling a hot piece of glass will cause the glass to shrink rapidly, creating structural stresses in the glass. If the rate of contraction is great enough, the glass will shatter. Pyrex is supposed to be stronger and more resistant to this phenomenon, but it can still occur.
One possibility is that the frozen dumpling did not heat up rapidly enough before it contacted the surface of your Pyrex pot. The point of contact was probably weak (possibly due to a manufacturing defect or extensive use of the pot) and when the frozen dumpling contacted the pot surface, that surface contracted rapidly, shattering the pot.
I shattered a pyrex casserole by putting it on a wet counter directly after I took it out of a hot oven. My assumption was that although it can go from the fridge to the oven, it just can’t do it in 10 seconds.
Yep, your cold dumpling hit hot glass, and the sudden temp difference made it break.
Fun fact: Pyrex will break in the opposite scenario as well, it just doesn’t happen as often because you have to get it really hot really fast. Once my chemistry teacher (working under a vent hood, BTW) poured 6M (concentrated) sulfuric acid into a paper cup sitting in a Pyrex beaker containing a mix of sugar, baking soda and something else (don’t remember, IIRC it had potassium in it). The acid reacts with the baking soda and produces heat (exothermic rxn). When heated, the something else reacts violently with anything organic. Sugar is organic.
When the acid finally soaked through the wax coating on the cup, purple flames and burning sugar shot 3 feet straight up. After about 2 seconds, the beaker exploded. :eek:
I love chemistry class 
Yup, what everyone said.
It’s not heat that breaks things, it’s the heat gradient (difference). Things generally expand when you heat it. When you heat something, generally it is heated only from one side, so one side expands while the other stays the same; this causes stress and eventually it snaps.
Pyrex is wonderful because the coefficient of thermal expansion is extremely small - it doesn’t expand much when you heat it. So it doesn’t bend much, and as a result, it can withstand fairly high temperature differentials. That’s why you can make cooking pots out of it. However, if you have one side heated by a gas flame and the other side cooled by a frozen or very cold food, it will cause enough stress to break the glass.
Pyrex is also used for telescope mirrors for exactly the same reason; it doesn’t expand (=deform) much when temperature changes. There are better material these days though, such as Zerodur (another type of glass). They are too expensive to use for cooking pots, however.
In college I took off a Pyrex lid from a casserole dish I was baking something in. The lid was really hot and I slighly burnt my hand. I ran some cold water over it and the lid was underneath the water.
KABLAM! I spent the rest of the day trying to get the pieces of Pyrex out of the garbage disposal while my physics major roommate gave me a lecture similar to what has been posted here.
Supposedly the very finest, thin wall glass wine goblets are able to withstand being filled with boiling water, even though the glass was originally at room temperture.
The explanation was that not only did heat radiate (transfer) through the thin glass more readily, but that, concomitantly, the thin glass was elastic* enough to expand without fracturing.
Any cites on this?
*Glass is not a solid but a hypercooled liquid. That is why very old windows develope sag lines.
Mrs. O relates a similar experience with Pyrex; to her shame she admits she knew these things happened and she went ahead and did it anyway - specifically running the casserole dish under cold water as soon as it had come out of the oven. Dunno if she had to spend any time cleaning bits of Pyrex out of the garbage disposal but I think it likely.
As for the OP, I can’t think of any explanation that would make more sense than Caldazar’s - the pot sticker wasn’t heated up enough when it hit the bottom of the pot. Ordinarily, I’m quite sure Pyrex can handle that sort of thing; this time around it may have landed on an area that had been deformed by heat stress to the point where it was weaker than the rest of the surface.
With regard to Zenster’s last line re: glass being a hypercooled liquid, as evidenced by sag lines. I have to disagree. In the days before the float glass process (not too long ago, I might add) panes of glass were made by a drawing a bar up through the pool of molten glass and pulling it up a very tall tower. The glass cooled on the way, but was sucepatable to sagging (picture taffy being lifted). Prior to that glass panes were made by pouring molten glass onto a metal plate (hence: Plate glass). In order to make the glass non distorting it had to be polished. Expensive and time consuming. Way back now…glass panes for the little house on the prairie were made by glass blowers. They would blow a bubble of glass, pop it and spin it like crazy. The resulting disk would be cut up into little panes (with the cheaper panes nearer the center; occasionally you can find a window pane with the nob included). If you picture this spinning disk the glass varies in thickness from the center to the edge. To minimize visual distortion it was customary for the glazier to hang the glass thick side down. At least the distortion from the panes would all be in the same direction. Below its liquidus, glass does not flow.
[chemical hijack]
Actually, all you need is conc. H2SO4 and sugar. The acid is hydrophylic (loves to absorb water). Sugar has all the atoms to produce water. The acid is hydrated by the water in the sugar,leaving a residue of balck carbon. The acid/water reaction is strongly exothermic, causing the water to boil.
This leaves a wonderful boiling mass of thick black (and highly acidic) gooey stuff wandering all over the chemistry lab.
Don’t try this at home folks.
I too love Chemistry class (even if it was 30 years ago)
[/chemical hijack]
Colin: Nah, this was much more fun. Bright purple jet of flames, loud noise, black goo, and toxic smoke (which leaked out around the edges of the window in the old vent hood :eek: ), and destroyed the beaker.
He knew it would do the flames and stuff–he just wanted to see if it’d break the Pyrex.
This is the same guy that, on the first day of school, brought in a balloon full of hydrogen, a balloon full of helium, and a candle on a stick.
Prof: “Pick a balloon…you might want to cover your ears when I do this…”
He balloon: “[sup]POP[/sup]”
H balloon: “WHUMP!” (accompanied by fireball)
Chemistry is fun! [sub](just don’t get too close to it…)[/sub]
Oft-stated by many, but incorrect, nonetheless. Glass is an amorphous solid. See http://www.urbanlegends.com/science/glass.flow/ for a lot of information on the subject. John Baez also has a good page about this. I could have sworn that Cecil did a column relating to this, but searching the archives I was only about to come up with this.
Hm, I take that back. Cecil did talk about it, but he was wrong. Solids are (admittedly arbitrarily) defined as having a viscosity larger than 10^14.6 poises, which is exceeded by glass at room temperature. But, as he notes that it would take billions of years for it to flow, I’m willing to give him the benefit of the doubt, and just call it a disagreement over semantics.
Was that Corning Visionware? Also did it actually say Pyrex on the pot? When I did Glass Technology way-back-when Corning had recently introduced a new and involved process which took a borosilicate glass (of which Pyrex was the Corning trade name) and removed the boron giving an almost pure silica glass. The resultant glass would have even better thermal shock properties than Pyrex. This was first introduced to the market as visionware in the early 80’s.
As to why it would shatter: glass is very susceptable to microscopic cracks. Through use it can pick up many of these, all too small to see with the naked eye. It may have been that your pot had picked up sufficient cracking to compromise its thermal shock resistance.
This reminds me of a demonstration done by my college professor. He set up three identical balloons, one filled with methane, another with hydrogen, and the last with acetylene. When he put a flame up to the last balloon, you could actually feel the compression wave from the explosion travel through the air if you were sitting in the first few rows of the lecture hall.
Of course, he then felt it necessary to pop a rather large balloon, without first disclosing the balloon’s contents, just to see how many people would panic (it was filled with He) 
We now return you to your regularly scheduled post.
I want to thank everyone who responded. It was illuminating reading. This incident occurred in 1987. The pot was Corning Visions and I am not sure whether pyrex was labeled on the bottom of the pot or not. I was just using the term as a generic descriptive term. One thing I do distinctly remember is that the frozen potsticker hit the bottom of the pot about three seconds after I dropped it in, I heard it clink to the bottom and the pot shattered soon after that. These details seems to confirm the hypotheses of those who responded.
Thanks,
Twinkle