Double boiling

[DabberDog]

I know not to set a glass container directly on a heating element.
What I've been doing is putting my glass container on a piece of cloth in a pot of boiling water.
Is it safe to put a Pyrex/Anchor quality glass container in a pot of boiling water without the piece of cloth?

[Allotrope1000]

I don't know about the cloth, but from my real, prior experiences:
1. Pyrex beakers/flasks of common solutions direct on a lab hotplate works for many processes like RSO.
2. Pyrex measuring cup used to melt chocolate bars for edibles direct in a pot of boiling water on kitchen stove works.

What does not work is:
1. Flint glass, like common jars and bottles, (not borosilicate glass like pyrex or kimax) in any heating operation. These are quite likely to crack. Flint glass lacks the superior thermal properties of pyrex.
2. ANY direct placement of ANY glass container on an open flame.
Guaranteed to crack/break. Don't do it. This is why a lab ring stand uses/needs an asbestos screen to protect the glass container when using a bunsen burner

Hope this helps.

[DabberDog]

Helps heaps! Just what I was looking for. Because of the small quantities I deal with, I need to find smaller jars I can heat in.
I love my Pyrex and Anchor bowls. They've been in a dry-ice/alcohol bath and now I can boil in them.

[Allotrope1000]

Go easy at first. Don't crank up the heat and walk away! Heat your solution up slowly and do not increase once you have a nice boil. It can possibly foam out of the flask making a hot, alcohol explosion risk, besides a sticky mess to clean up. Wear eye/face protection.

[Allotrope1000]

Oh, btw, never put dry ice temperature glassware on a hot hotplate - asking for disaster. Warm the glassware first, then start with a room temperature hotplate.

Go to online and buy some pyrex lab glassware of a size for your batches. Pretty cheap. Quality and the right tools for the job.

[Ckbrew]

What Allotrope1000 said. If you are using good borosilicate glass you most likely will not run into breakage. Just remember it is glass so you can never be 100%. If something has a defect it will show up shortly after using. One thing I can add is bumping. This is when the liquid superheats due to being stuck under something usually flat with a little concave, then burst forth suddenly into vapor. This is what causes the rattle in the boiling pot one might heat in a home canning process if they are not using a rack and putting the jars directly on the bottom of the pan. Sometimes flat bottom labware containers like an erlenmeyer flask or beaker gets bumping hard enough it may crack the glass just from all the banging around. It is the type of thing that will present itself if say there is just the right concave in the bottom of one flask while all the others are fine. Rare but it is a possibility. If you run into severe bumping add a trivet under the glass container. That will allow for easier escape of the steam vapor. A piece of metal mesh would work as a trivet. Your cloth was acting like a trivet. If you examine the bottom of a canning jar they have small bumps in the lowest ring of glass on the bottom of the jar. Built in trivet.

How small of a size are you talking about for your process jars? Back when I was growing up yeast cultures for beer I used baby food apple juice jars. I think they were 60 to 100ml and not terribly expensive, perfect size for starting a yeast culture from a loop swipe off an auger slant. I used a one hole stopper with some cotton in the hole, then sterilized them in a pressure cooker before making the yeast starter. Never had one break.

[Ckbrew]

How many people are checking the bottom of their jars right now?

[DabberDog]

Thanks for the input, y'all.
Funny about the bumping. The cloth under the bowl in the pot of water stops the buildup in the concavity.
For (I'll call it) a dipping jar, you want smoothe sides. Lid should be one piece, not childproof or have a paper or removable plastic lid insert. It is hard to clean childproof lids and inserts, and remove liquid extracts out from under the shoulder of a glass jar. Baby food jars are just the right size and one-piece lid construction, but I only know them with the shoulders. 1/2-1 cup mason jars are great for storage. Process needs at least a quart glass bowl and double boiler friendly.

[2ShedsJackson]

Worth noting that not all Pyrex is Borosilicate, some is cheaper, lower quality soda-lime glass.
If it's marked PYREX ( all capitals ) it's Borosilicate. If it's marked Pyrex then it's Soda-lime

[DabberDog]

Good warning to everyone 2ShedsJackson. One is the real deal the other is a modern-day misrepresentation.
Gotta go check to make sure about mine.
Anchor is another good brand.

[DabberDog]

Dang. I'm all lowercase. They've worked for me so far but now I'm paranoid.
Thanks for making me paranoid, 2SJ.