On Thu, 12 Jan 2006 09:07:48 GMT, Lobster
wrote:

| Dave Fawthrop wrote:
| On Thu, 12 Jan 2006 08:23:54 -0000, "Grumps"
| wrote:
|
| | I've always been told that you shouldn't use water as it could crack the
| | glass. Is this true or one of those old wives' tales?
|
| There is a standard way of breaking glass bottles cleanly to form a
| ?glass? using boiling water. So boiling water definitely breaks glass.
|
| It's all about temperature differences surely, and changing temperatures
| quickly; the reason glass breaks is because it expands when it gets hot,
| and if that happens too quickly the glass won't warm up evenly,
| resulting in breakage.
|
| Consider the following:
|
| 1. Take a wine glass out of the cupboard and fill with boiling water -
| it's unlikely to break.
|
| 2. Put it in a pan of cold water and bring to the boil on the cooker -
| again, not likely to break.
|
| 3. Put the empty glass in the freezer for a while, then remove and fill
| with boiling water - it'll almost certainly break, due to the rapidity
| of the large temperature change.

True but pouring boiling water onto a windscreen will produce a large
temperature difference, and so may crack the windscreen.
--
Dave Fawthrop dave hyphenologist co uk
17,000 free e-books at Project Gutenberg! http://www.gutenberg.net
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