Sciencemadness Discussion Board - How much sand / oil is generally needed for a heating bath?

How much sand / oil is generally needed for a heating bath?

Nitrox2 - 1-7-2025 at 17:21

Something tells me the capacity of this cut up soup can is a lot less than what I'd.

Looking for suggestions here.

charley1957 - 2-7-2025 at 03:25

Some questions have no simple answer. Often it’s best to just try it. Run some tests. Use sand. Use oil. More sand, or less, whatever gets the job done. Just try it. Use a bigger can, or a smaller one, or a bigger hot plate. Boil water. Learn by doing.

[Edited on Jul07-2-2025 by charley1957]

Cathoderay - 2-7-2025 at 07:07

The first time you heat that can you might find that there is a coating on it that may burn off. For that matter the sand you use may not be clean. Best to do things like that outside or very good ventilation.
If you are in the U S you could try second hand stores like "Good Will" for pots and pans.

Radiums Lab - 2-7-2025 at 07:48

What is the capacity of the flask you are heating ?

Nitrox2 - 2-7-2025 at 08:16

Sieved the sand, rinsed it in tap water, and now drying it on the hotplate.

Thinking that the residual water will aid in heat transfer allowed jg my sand to get hot faster -- than I expect it to smoke smoke as it is (debris burning off in the sand. (At least the lower portions nearest to the heat. It probably needs to be stirred.)
I'm noticing a good deal of condensation on the inside of my test tube, which reminds me of jsum1s post about short path distillation relying on evaporation. I forget whether or not he said this could be done without vacuum as well.) *

I will be going out today and hope to find a bigger pot.

I have little idea of how big I can go with this burner, I guess it depends upon allt such as how big of a flask and how hot do you want it to go.

[Edited on 7-2-25 by Nitrox2]

Nitrox2 - 2-7-2025 at 09:07

Looking for suggestions advice

Perhaps a little metal cup and put my flask in that cup, that way if I'm the flask breaks I could still possibly gather the reagents from the cup.

This would be more of a direct heat option, without using a bath.

Nitrox2 - 2-7-2025 at 09:22

Going to ditch the sand and use mineral oil : (

Didn't want my glassware getting oily, the hazards, and not being able to recover products -- but ;/

Hopefully I can find a pot that will work. Not sure how big of a flask I can do with oil, but from some recent reading I hear that I'll be able to do a bigger flask with mineral oil.

Hmm.
Going to run some more tests
Advice?

[Edited on 7-2-25 by Nitrox2]

BromicAcid - 2-7-2025 at 09:25

Sand baths are not very efficient. Sand is a reasonable insulator, you're making that sacrifice to help with uniformly heating the bottom of your RB flask. Basically, it's always a compromise, remember that if you heat too aggressively the insulation properties of the sand can result in burning out the heating element. I have seen aluminum beads and copper shot used in place of sand.

Oil baths are generally better (heat transfer) but a bit messier. The advantage to using a sand bath is higher temps without smoking.

Nitrox2 - 2-7-2025 at 09:34

Maybe this pot with mineral oil would be a better fit.

It is a little larger than the hotplates 3.9" diameter. I hear that's bad.

Probably will take the long goofy handle off.

Nitrox2 - 2-7-2025 at 09:39

I previously thought that sand was better for a slower gradual change in temperature but then read that sand is prone to hotspots.

Nitrox2 - 2-7-2025 at 09:41

Quote: Originally posted by BromicAcid

Sand baths are not very efficient. Sand is a reasonable insulator, you're making that sacrifice to help with uniformly heating the bottom of your RB flask. Basically, it's always a compromise, remember that if you heat too aggressively the insulation properties of the sand can result in burning out the heating element. I have seen aluminum beads and copper shot used in place of sand.

Oil baths are generally better (heat transfer) but a bit messier. The advantage to using a sand bath is higher temps without smoking.

Saw this on Gemini

"Sand doesn't make a good heat bath because the air trapped between the sand grains acts as an insulator, which hinders effective heat transfer. While sand itself has some insulating properties, the air pockets are the primary reason for its poor performance as a heat transfer medium for a uniform heat bath."

Deathunter88 - 2-7-2025 at 10:50

Wax is another option, same heat transfer properties as oil but if you leave your flask in until it solidifies you can just pop it out without any of the mess.

Nitrox2 - 2-7-2025 at 11:21

Here is my pot

Morgan - 2-7-2025 at 11:50

Would salt work as well as sand just out of curiosity? There are also those slabs of Himalayan rock salt used as preheated cooking surfaces.

Radiums Lab - 2-7-2025 at 12:01

Yea salt works great, but if it has moisture then it starts bumping on sudden temperature rise.

Radiums Lab - 2-7-2025 at 12:02

Try to use pure salt, or oven dry the store one before using.

[Edited on 2-7-2025 by Radiums Lab]

MrDoctor - 2-7-2025 at 14:23

theres 3 oils you can use, "paraffin oil" sold at most hardware stores, i observed no smoking up to 200C, didnt run it higher though. at under $10/L it doesnt really matter if you lose some, a decent bath for a 500ml flask needs like 500-800ml, the losses are trivial in cost.
then theres common silicone oil, supposedly also good to 200-250C but with no long term degredation, though its not designed for heat bath use, just by chance it works. then theres actual purpose made high temp, i think methyl-silicone oil? i think its stable over 300C, its high temp machine lube but the generic form is very close to actual purpose-made bath oil. this stuff is normally expensive but does exist in a cheap form for like $20-40/L

if you have the means to, you could try sand-casting an aluminum block heater, and a lazy way to heat that would be to buy high temp cartridge heaters, they glow red hot, use 300-500W and cost about $6-15, resembling larger versions of the ones used in 3D printer hotends. using them would be as easy as drilling out several holes partially casted for them in the block heater. adding a void to the bottom of the block and the fact theres no need for elements directly at the bottom also opens up the opportunity to use such a thing with a magnetic stirrer.

Lastly, there are solder recipes that dont use lead or cadmium to get low melting points, and while they benefit from gallium, thats not essential either. indium by itself melts at 156C and the addition of tin lowers that, and bismuth to a degree can bulk it out without a massive impact on the melting point.
while containing lead, Cerrolow 136 doesnt even use that much expensive indium, mostly bismuth, for a liquid melting at 70C. chipquick and fields metal need a lot more indium but are lead free. the addition of gallium should destroy their physical integrity assuming they stick to the glass at all, preventing cracking, though gallium itself will actually cause adhesion too so, check before adding gallium. galinstan alloy which melts at below zero coats glass like its mirror-paint, but it comes off easily under high pH

[Edited on 2-7-2025 by MrDoctor]

Nitrox2 - 2-7-2025 at 15:05

I tried getting a SS bowl from the pet store that is a little less heavy than the TFAL pot. I was also hoping for a better fit than the TFAL pot by getting the pet bowl.

Pet bowl holds 1QT it says, the TFAL bowl has holes in the sides, but I likely wouldn't need to fill it that full.

I also picked up 2 pints of mineral oil for a heating bath medium, though my sand is still drying, I may give that another go.

Which bowl would you say?

TFAL bowl is 5 1/16"
SS pet bowl is 4 1/4"

Still a little bit overhands but not much
Hotplate surface is 3.9"

SS pet bowl is a lot lighter, fits the hotplate with less overhand
And I think I'll go with it

Though the TFAL pot looks nicer on the hotplate, I think.

[Edited on 7-2-25 by Nitrox2]

Nitrox2 - 2-7-2025 at 16:51

I think what I have here is correct for most types of distillations (solvents afaik)

For a flask no larger than 100mL

Round bottomed, so the majority of the flask isn't out of the heating medium, acting as a heat sink -- like this brown bottle of about 100mL

[Edited on 7-3-25 by Nitrox2]

jackchem2001 - 2-7-2025 at 19:18

If you are doing low temperature stuff (<200 degrees) I would recommend an air bath: https://www.sciencemadness.org/whisper/viewthread.php?tid=16...

Cathoderay - 3-7-2025 at 13:50

I don't think any brown glass is pyrex so I'd be careful of heating it.
Also I'd be careful of burying the test tube or flask too far in the sand. You need to see what is going on, never boil something to dryness. If you boil dry the temperature can rapidly climb and the residue can burn and/or the glass will crack.

By the way, I noticed in one of your picture that there is a red blower box. That blower would be a good starting point for lab ventilation. Block off most of the window opening except for an outlet from the blower. Of course with the motor in the air stream it would not be safe from flammable or corrosive fumes.

Nitrox2 - 3-7-2025 at 14:10

I'm going to be investing in some new flasks, not sure if I can make do with 1 500mL beaker, and a few Erlenmeyers.

but am thinking this is the lowest price set that offers the biggest bang for the buck

Point noted about the blower, I still wonder how all the window could be setup for a fume hood. Harbor freight had a different but similar model. Someone I knew once modified it with some sort of air ducting flange, and rivets, that way it could have 6" diameter duct tubing ran from it. It is a quieter fan than the can fan hydroponics fans!!! I've heard that the blower would work, depending upon the size of the hood, and how quickly the air turns over, etc, it could dilute the flammable vapors without igniting them. Not sure on all of the details, but I do believe the fan COULD help.

Is doing chemistry outside in the open-air better or worse than a fume hood? We do have a screen room here, which is where I've burnt off the manufacturing oils from my hotplate, and setup my sand

I'm going to keep it a little simpler, the heating bath will likely rairly be used, for a lot of applications, I can go straight to the hotplate with a beaker or Erlenmeyer flask

Anymore informaton on distilling to dryness? What if I have 7mL of a highly valuable solution. If I don't distill it ALL or down to a very very small amount, I will lose very very valuable product.

[Edited on 7-3-25 by Nitrox2]

[Edited on 7-3-25 by Nitrox2]

[Edited on 7-3-25 by Nitrox2]

Precipitates - 3-7-2025 at 19:15

Quote: Originally posted by Nitrox2

Is doing chemistry outside in the open-air better or worse than a fume hood?

I would say a fume hood is better, but open-air is safer (and potentially cleaner).

The risk is more if your fume hood stops working for any reason. What if there is a power cut? Or some other problem.

Large laboratories have generators, which can rapidly supply power in the event of an outage.

Upon handling very toxic chemicals I would ideally use a fume hood and a respirator, so that there are two points of failure in case of any problems.

Quote: Originally posted by Nitrox2

Anymore informaton on distilling to dryness? What if I have 7mL of a highly valuable solution. If I don't distill it ALL or down to a very very small amount, I will lose very very valuable product.

Distilling to dryness is okay, you just have to be very careful with the heat. The issue is more going to be ensuring these last few drops of product come over. There will always be some product lost in the apparatus.

MrDoctor - 3-7-2025 at 20:15

a low end cheap UPS should be able to power your fumehoods extractor fan, but this doesnt save you if the fan itself fails.
its important to consider, what do i do if things go wrong when im creating deadly gasses

jackchem2001 - 4-7-2025 at 00:12

In regard to distilling to dryness: imagine you are distilling water at atmospheric pressure. The temperature in the flask is basically limited to 100 degrees. Any additional heat you input will be absorbed by the latent heat of vaporisation of water.

Now imagine the flask runs dry. The flask will rapidly heat up. Here comes the problem - what happens if the distillation head is a bit cooler and some water condenses and drips back down into the boiling flask? The spot where it lands will cool rapidly and this can crack the flask.

In regard to doing chemistry outdoors: it is a huge pain in my experience and I almost never do it. I don't have a fume hood either. I manage fumes by:

assembling apparatuses with greased joints
leading exhaust gases into a scrubber. Use a check valve to prevent suckback, and use a bleed valve on the apparatus too
having an air pump (and a spare) available to purge apparatuses of gases
fans for ventilation

If you choose to do it like this (indoors without a fumehood) be aware that there are a couple of experiments you can't do. E.g. you can't really work with Cl2 or do a nitric acid distillation. Have to do these experiments outside, but you can handle a bit of NOx perfectly fine.
Also do not be tempted to use a respirator - if you are doing this regularly then you need to improve the setup (though sometimes it is a bit unavoidable such as when cleaning glassware).

[Edited on 4-7-2025 by jackchem2001]

Nitrox2 - 4-7-2025 at 07:50

What about adding a higher BP compound to the distillation flask?

In regards to distilling to dryness

Cathoderay - 4-7-2025 at 13:00

As far as outdoors vs. fumehood, it somewhat depends on the weather and what gases might come off the process. From your pictures it looks like you live in a nice climate, (southern California I would guess) so outdoors would be fine, but if you want to do chemistry and it's winter in Boston that would be a different matter. I wouldn't stand down wind anyway. Distilling alcohol would be pretty safe indoors with some fresh air but if distilling nitric acid or making chlorine, bromine, hydrogen sulfide gas, etc. indoors you better have a fume hood (probably a gas mask also). So it depends on what exactly you are doing.
By the way do you live in a house or in an apartment?
If an apartment you need to be extra careful, you could get into a lot of expensive legal problems if you damaged something or effected the neighbors.

On the subject of boiling to dryness and your valuable substance, no chemical process delivers 100% yield, some is always lost. You could evaporate to dryness (low heat) OK.
You could dilute the substance with more solvent so that the little left in the flask will have less substance percentage wise.

zed - 5-7-2025 at 16:18

Utilizing oil baths, I have always failed. If you need high heat; a heating mantle is generally the best way to go.

CuriousOnlooker - 23-7-2025 at 07:42

Quote: Originally posted by Nitrox2

What about adding a higher BP compound to the distillation flask?
In regards to distilling to dryness .. Hotplate surface is 3.9"

I'm jumping into this conversation because, maybe I missed it, but I don't recall you saying what you were going to be doing, other than distillation which could mean many things.

Quote: Originally posted by Nitrox2

not sure if I can make do with 1 500mL

That's a very large jump from a test tube or bottle, which leads me back to my earlier query.

I wouldn't trust the brown bottle for any heating, other than warm.
You will do yourself a great service by getting the 500ml beaker.
When I've used a sand bath I like to have the sand extend ~0.3 of the way up the flask to ensure a larger heating area, however I use a round-bottomed flask for such things and the curvature of the metal bowl closely matches the flask. Sand baths do take a long time to heat up, but that doesn't mean they should be rushed as it will be too easy to over-heat.
Invest in a thermometer or infra-red temperature reader.

I would like to reiterate what a couple of others have said, namely:
@charley1957: "Boil water. Learn by doing."
@Cathoderay: "careful of burying the test tube or flask too far in the sand. You need to see what is going on, never boil something to dryness."

It will serve you well to do a test run with water.