# Using a electric Hotplate.



## viacin (Oct 5, 2008)

I'm seeing a lot of stories about beakers bursting when heated on a electric hotplate or stove and not gas. I see how the electric could be a harsher and more concentrated heat than the gas, but are there any real dangers here of your beakers bursting on a electric hotplate as opposed to a gas?


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## Lou (Oct 5, 2008)

What stories are these? I've used the same beakers for years on the same hotplate without any problem.

If anything, it is more likely that gas would break glass than a ceramic hotplate.


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## viacin (Oct 5, 2008)

"every time i've ever read anything anyone has written about starters and flasks they always said how convenient it is to just put the flask right on the burner, so i said why not, one less pot to wash. right after it started to boil i heard a loud pop and there was a circular crack all the way around the bottom! WTF?! is it because i have an electric stove? "

"I use my flasks with a gas stove and have no problem going from boiling to an ice bath"

"Well, i've done a bunch of chem classes, but we never heated with electric ranges. Gas heat is much more "gentle" and less localized than an elictric element. Thus , when you use Pyrex on an electric stove, you have a piece of wire in the shape of a star that sit between the flask & the heating element."

" Usually, though, you don't heat with an electric element directly. In chemistry practice, you'll use a "sand bath" where the sand acts as a medium between the element and the glass. That, or use gas."

"Mine cracked on my electric stove the second time I used it."

I don't know, maybe they are all idiots, or got a bad lot of flasks. Not likely, but possible. 

*how about the $10 - $20 single electric coil burners you see?* Are they more likely to crack the glass?


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## qst42know (Oct 5, 2008)

Electric range type coil hot plates are cheap and can be used if they have a variable thermostat (not high, medium, low) but put a piece of aluminum plate 1/4"-3/8" on top. They are usually a much higher wattage than lab types. Drips leave stains but are quickly neutralized by the aluminum. Lab type ceramic top hot plate with stirrer is on my wish list, but out of my budget right now. 

Chris


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## viacin (Oct 5, 2008)

same here, but I did see a ceramic top hot plate with stirrer end on ebay today for about $50 + S&H. It was old though, but probably still had some life left in it.

A new one is on my wish list too.


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## Lou (Oct 5, 2008)

And who do you attribute these quotes to and when? How am I supposed to know that some 14 year olds didn't say that?

I've used hotplates almost everyday for many years and I've rarely had issues with thermal shock, usually it's with bumping. I've also used methane fired Meker burners (think of a hotter Bunsen or Tirril) and had glass and even Coors porcelain crack when I put it into the flame. 


Cracks from thermal shock occur because the glass can't expand quickly and uniformly enough to cope with the heat causing a pressure differential from one area to the other which causes cleavage from layer to layer, meaning a crack. Now let's use your head and think logically, what is more likely to crack glass if its related to dissipation of high heats: a gas burner which has a 1050-1500C flame (depending on area) or a 200C ceramic top constant across the surface?


qst24know that is a very good technique that is very well used and known but it suffers from the short coming that fumes generated in the process will take a toll on the aluminum especially when hot. I use it for drying precipitates--a hot plate isn't needed directly.


Lou


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## viacin (Oct 5, 2008)

I found these quotes on http://www.homebrewtalk.com/f11/why-did-my-bomex-flask-crack-40602/ If you search the web you can find several other forums. It can't be just them having these problems. I highly doubt that a 14 yr old would be brewing his own beer, but I wouldn't put it past some.

I have never had one break either, mainly because I've never done it. It seems to be a divided issue, with as many ya's and na's. But I'm here to find the truth. Don't worry Lou, relax, I take your word for what it is, an expierenced refiners.


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## Lou (Oct 5, 2008)

I brewed my own beer when I was 14


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## Oz (Oct 5, 2008)

At what age were you distilling your fermentations?


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## lazersteve (Oct 5, 2008)

Another cause of sudden thermal fracture of pyrex beakers and flasks are what's known as star cracks or fractures. These cracks come from the flask being hit hard against another flask or surface. 

They are not always obvious to the untrained eye and can result in the container shattering when heat stress is applied. They appear as a small criss cross pattern like a star (hence the name) in the glass. They usually appear around the bottom curved part of the container.

For this reason always inspect your glassware before you heat it to be sure there are no star fractures present before using. If you find one, discard the flask.

Steve


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## Harold_V (Oct 5, 2008)

Speaking from the position of a guy that used a gas hotplate for his entire refining career-----you can break beakers, regardless of the type of heat you choose. 

One of the problems I encountered on a regular basis was when refining polishing wastes. After thorough incineration and screening, they were subjected to a heavy boil in dilute HCl, to remove base metals and other substances that often make filtration difficult after the values have been dissolved. 

Unlike Lou's scenario, bumping was rarely a problem in this operation, but solids accumulating on the bottom of the beaker, isolating the solution from the glass, was. The isolated area would get over-heated, then when the lot was stirred you'd experience an instant cracking of the beaker. 

To solve the riddle, I got in the habit of stirring almost constantly, but that destroys the beakers in short order. The polishing wastes are generally filled with abrasives that erode the glass surface of the beaker as they're ground between the glass rod and beaker during stirring. Bad part was that the beakers were always large---3 or 4 liters. 

I used gas because my hotplate pulled double duty, and, I must say, it served me very well. The left burner was set extremely high, so I could incinerate. The burner could still be used for evaporation and other processes, so I found myself running three burners almost constantly, unless I was incinerating. 

Can't speak for the habits of others, but I routinely used a gauze pad, or an asbestos pad under my beakers. It provided the small amount of cushioning that helped prevent breaking beakers that were set down hard on the hard surface, plus minimized localized heating. 

I'm not convinced I'd use the surface of any heating device without a pad unless it was one like Lou described, where the temperature was not excessive. You can't rely on that from gas or electric. 

Harold


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## goldsilverpro (Oct 6, 2008)

I always placed the beaker, no matter what size, in a 5 quart, flat, white Corning Ware dish and then placed the dish directly on the hotplate, in case of beaker breakage, foamovers, or drips. Better safe than sorry.


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## viacin (Oct 6, 2008)

good advice gsp


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## qst42know (Oct 7, 2008)

These Beer Brewers go directly from full boil to the ice water bath to cool their wort. A severe test of even the best lab ware. I would be surprised every time their vessel didn't break. Fortunately refining doesn't require such extremes in such a short time. With some transition time even Mr Coffee will hold up.

Chris


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## Sylar (Oct 10, 2008)

I have to disagree on that one.

As a fairly experienced amateur experimentalist, I own quite a bit of good quality glassware that can go from 200°C (and probably higher) to ice water and this multiple times over without breaking. Ofcourse scratched glassware (even higher qualities) is allways much weaker then pristine.

There is just no substitute for good quality borosilicate glassware.


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## Noxx (Oct 10, 2008)

Yes and beakers don't cost much. Maybe 5$-6$ for a 500mL one.


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## Harold_V (Oct 10, 2008)

Sylar said:


> There is just no substitute for good quality borosilicate glassware.


I went through beakers at a rapid rate, due in part to the abrasion from processing waste materials----polishing residues and bench sweeps. The surface of the beaker was abraded badly, cutting short the lifespan. Still, I kept using commercial beakers instead of other ware. They were expensive, but provided the best possible vessel for the purpose. 

Harold


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## viacin (Oct 10, 2008)

I decided to buy two pyrex 1000ml beakers. no sense in saving $10 if it costs me $100 in lost product.


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## goldsilverpro (Oct 10, 2008)

Buy a white flat Corning Ware dish and put the beaker in it while heating. Saves a lot of grief.


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## viacin (Oct 11, 2008)

OOh yeah, a great idea gsp. Been on my list since you first recommended it. I'm going to town today and have a look around for one.


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