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A few days ago, I was creating a solution which involved boiling water. I had two 4L beakers on identical hot plates. After around 10 minutes, the first one boiled. Waiting another 30 minutes, the second one had still not started boiling, although small bubbles had formed at the bottom. Shortly afterwards, I heard a ping and the second beaker cracked and leaked water.

Is there any possible correlation between the long boiling time and the beaker breakage? Both beakers should have been heat-safe, although they were from different brands. I'm not convinced of the cleanliness of the beakers, so if this could've been caused by a contaminant, that's a definite possibility.

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  • $\begingroup$ Was the beaker bigger than the hotplate? A famous experiment was done with 10" glass frying pans. The pans were put on small stove eyes. Several pans exploded while others did not. This is why 10" glass pans are not sold. $\endgroup$ – Agriculturist Feb 28 '16 at 8:58
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I'm inclined to suspect that your identical hotplates were less identical than you think. They can have substantial differences in heating rate as well as the actual temperature they reach, particularly if they have been around for a while. You could try boiling another pair of similar beakers and check the time they take to boil to confirm.

Usually lab glass breaks because of thermal shock - either hot glass with cold water or cold glass with hot water. However, if you heated the beaker steadily for 40 minutes, it definitely wasn't shocked into breaking. An exception might be if the hotplate is malfunctioning and get extremely hot extremely quickly, but that doesn't seem likely. It is definitely possible that there was already a small crack in the beaker and that heating caused it to open further.

A contaminant is very unlikely to have been the source of the problem. You should be able to boil dirty beakers all day long without them popping on you.

Unfortunately it's pretty much impossible to tell what happened for sure unless it winds up being reproducible.

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  • $\begingroup$ Uneven heating on the hotplate surface could be another explanation. Since the second hotplate seemed to take much longer to boil, it seems that it may not have been heating correctly. $\endgroup$ – MaxW Feb 28 '16 at 5:09
  • $\begingroup$ Questionable hot plates are definitely a possibility -- to the best of my knowledge, I'm younger than either. I can check to see if anyone else has encountered any issues with them on Monday, but I haven't heard anything recently. $\endgroup$ – Nathan Ringo Feb 28 '16 at 6:33
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Generally you should put boiling stones in a liquid to reduced "bumping." Basically the vessel becomes hotter than the boiling point and all of a sudden a large bubble of the vaporized substance forms. As you have verified the bumping can be violent enough to crack the vessel.

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  • $\begingroup$ Wow, seriously? That's nuts. If this is the case, boiling should have occurred as the beaker brokem. @tikiking1, did the water in the second beaker boil violently once the glass broke? Based on your description, it doesn't sound like it bumped at all. $\endgroup$ – SendersReagent Feb 28 '16 at 4:45
  • $\begingroup$ Though I agree that boiling stones should be used, if small bubbles had formed, the water didn't bump. $\endgroup$ – Jason Patterson Feb 28 '16 at 4:55
  • $\begingroup$ I was thinking that "exploding" in the title meant what I was calling bumping. If the beaker "just cracked" then it was probably uneven heating causing uneven thermal expansion of the glass. $\endgroup$ – MaxW Feb 28 '16 at 5:20
  • $\begingroup$ I didn't see anything like a big bubble, but I wasn't watching the beaker until I heard the ping noise. It still wasn't at a rolling boil when the heat was removed. The exploding was what happened when attempting to move the beaker onto the table; the bottom fell clean off. $\endgroup$ – Nathan Ringo Feb 28 '16 at 6:28

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