I made a thread some time ago about how to heat stuff to ridiculous ends, but I'm still confused about how to cool it. I know how to make an ice bath
and put my beaker in it, but that only gets down to 0-5C. I know what dry ice and liquid nitrogen are, but I'm not sure how to get them, and I'm not
sure how to keep them cold. Anyone care to share their experiences?Megamarko94 - 3-9-2011 at 11:20
dont worry about keeping liquid nitrogen and dry ice cold they will stay cold by them self..
liquid nitrogen must be kept in container called dewar its a container with double walls and vacuum in the between. (never keep it in close container
because it will go boom from it going to gas stage)
you can put thermal foil around block of dryice to keep it solid longer.
i dont think they sell liquid nitrogen to individual
[Edited on 3-9-2011 by Megamarko94]Acetic Acid - 3-9-2011 at 11:24
I feared that... and it's hard enough to get dry ice as well because I'm under 18 >.<Megamarko94 - 3-9-2011 at 11:28
and dewars are pretty expensive...UKnowNotWatUDo - 3-9-2011 at 11:29
Dry ice can be mixed with acetone (or sometimes ethanol) to make a cooling bath which will keep your reaction mixture at about -78C. If you can't buy
dry ice directly you might try getting someone to buy it for you. I wouldn't imagine it would be that hard to find someone to buy you something as
innocuous as dry ice. Maybe a friend or parent?Acetic Acid - 3-9-2011 at 11:35
Ah yes, I remember a youtube video where this guy froze acetone with liquid nitrogen. Same concept I guess?Endimion17 - 3-9-2011 at 11:38
I made a thread some time ago about how to heat stuff to ridiculous ends, but I'm still confused about how to cool it. I know how to make an ice bath
and put my beaker in it, but that only gets down to 0-5C. I know what dry ice and liquid nitrogen are, but I'm not sure how to get them, and I'm not
sure how to keep them cold. Anyone care to share their experiences?
Here, knock yourself out. Megamarko94 - 3-9-2011 at 11:38
i think that guy was nurdrage...
[Edited on 3-9-2011 by Megamarko94]Acetic Acid - 3-9-2011 at 11:39
Thanks! Isn't it possible to get calcium chloride as road salt?? Now I know why :->Endimion17 - 3-9-2011 at 12:12
Thanks! Isn't it possible to get calcium chloride as road salt?? Now I know why :->
Don't mention it.
No, road salt is a mixture of calcium and sodium chloride.
But relatively pure calcium chloride is that stuff you buy for removing moisture in damp rooms. For some reason, that tends to be expensive where I
live.
It's usually packed in some synthetic cloth and is placed in special trays.Acetic Acid - 3-9-2011 at 12:13
barley81 - 3-9-2011 at 13:33
A brand is Damp-Rid sold at Home Depot, it comes in cartons and cylindrical plastic containers with snap-on lids. Just thought I'd add something...
Also if you can find an Airgas near your home, it will carry pellets of dry ice, sold in boxes for $10.ziqquratu - 4-9-2011 at 19:37
Dewars are cheap - as long as you buy them in the form of a Thermos flask or similar.
As mentioned, though - do NOT seal any container which holds dry ice or liquid nitrogen, or it WILL explode, violently! A loose-fitting polystyrene
foam plug serves as an excellent cap - it should allow gas to escape, but on the off chance it does seal (eg if it's wet and you get an ice seal
forming), it should pop out under low pressure and cause much less damage than an exploding flask.Endimion17 - 5-9-2011 at 03:07
I've never seen a big thermos flask. Only up to 2 liters, and that's only for keeping a sample right before you do the experiment. The larger the
flask, the longer it keeps the stuff at the same temperature. That's why Dewars are 50, 100 liters etc.
If he's going to work with LN2, either he has to have a quick access to a near filling station, or buy a real Dewar.
Dry ice can be stored in iceboxes with styrofoam walls added. Again, the more you have, the better.Dr.Bob - 9-9-2011 at 10:03
You can get dry ice at many grocery stores or ice cream places (especially if they sell ice cream cakes). Our Kroger's sells it, for one example.
We have plenty of places nearby that sell it. Just look in the phone book (a paper thing invented before the internet) under dry ice. It is not
regulated as far as I know. You could also try searching Google maps for dry ice.Neil - 9-9-2011 at 10:17
Curiously the larger the vessel the shorter it keeps 'the stuff'. more surface area, a 1L dewar losses less N2 then a 25L dewar in the same period.
But with a larger vessel you have more of the stuff so losing a bit of it isn't much of a worry. If you get to use half the nitrogen out of a 180L
dewar you are doing very well.
Getting small dewers that are insulated as well as the large dewars is the trick, most of them are not nearly as good.
Calcium chloride is sold by people who sell cement in cold climates, it is also sold where people use it as a additive to remove dust from gravel
roads during hot dry summers.
Dollar stores often carry small containers of it as a 'drying agent' ditto with boat or RV stores.
The last bag I bought of it was around 34$ for 65 Lb and it was labeled for treating summer roads. Panache - 9-9-2011 at 21:29
conc sulfuric poured onto crushed ice is a super cooling bath for freezing something in a pinch, the normal precautions concerning sulfuric pertain,
afterwards you'll have a solution of sulphuric acid that can be used as sulphuric acid solutions are. Driving off the water at temp allows you to
repeat the process with fresh ice.Sedit - 10-9-2011 at 07:59
I never had luck with H2SO4 on ice, Concentrated Sulfuric worked worse then dilute. HCl onto snow on the other hand worked wonders.sternman318 - 10-9-2011 at 09:09
Dry ice can be mixed with acetone (or sometimes ethanol) to make a cooling bath which will keep your reaction mixture at about -78C. If you can't buy
dry ice directly you might try getting someone to buy it for you. I wouldn't imagine it would be that hard to find someone to buy you something as
innocuous as dry ice. Maybe a friend or parent?
I bought some "DampRid Moisture Absorber Refill". I got 4 pounds for $5.29 from my local Publix. Opening it up, the chips look like pure calcium
chloride, and when I left some in a beaker overnight they were a solution by the morning. How do I chill the solution to its freezing point, though?
My freezer won't cut the mustard. Do I leave it in a dry ice bath until it freezes?
Look to the "end of the fridge pump questions" thread for some basics on how to get cheap compressors.
A basic fridge compressor or AC unit can get you quite a ways, but if you are willing to play with some exotic refrigerants you can start looking into
cascade cooling(the use of several refrigerants in a loop, with each evaporator cooling the condenser of the next coolant phase). This sort of
cooling, with two units and good refrigerant selection can produce temperatures low enough to freeze carbon dioxide and produce dry ice, or provide a
cooling coil which could easily cool an acetone reservoir and allow cryogenic temperatures.
Some people have even used cascade cooling and a small cryocooler to produce liquid nitrogen DIY style, but it should be noted that this will also
condense liquid oxygen and as such is a rather dangerous extremeunionised - 11-9-2011 at 05:15
In any event, if you have, for example, 100 litres of liquid N2 to look after you will have more of it left at the end of the week if you put it in
one 100 L dewar rather than 100 1 litre ones. Endimion17 - 11-9-2011 at 05:27
Curiously the larger the vessel the shorter it keeps 'the stuff'. more surface area, a 1L dewar losses less N2 then a 25L dewar in the same period.
But with a larger vessel you have more of the stuff so losing a bit of it isn't much of a worry. If you get to use half the nitrogen out of a 180L
dewar you are doing very well.
Getting small dewers that are insulated as well as the large dewars is the trick, most of them are not nearly as good.
That's simply not true and I'm stunned to read this.
If that was true, it would be stored in small vessels. Economy argument.
And another argument, this time natural one, is that surface grows slower than volume, if the body is close to being spherical, which is the case of
LN2 tanks.
LN2 is spent by increasing its storage tank surface. Nitrogen inside LN2 does not evaporate. Only the layers touching the vessel do.Neil - 11-9-2011 at 09:19
The larger dewars are tall cylinders to conserve floor space, the lower volume ones get to be shorter and fatter.
If the Dewar shapes where the same and the sized changed certainly but in practice I found that LN2 is lost faster in a commercial tall 180L then a
shorter fat storage 25L. In a good brand new 1L vessel the loss is almost unnoticeable.
I calculated it out back when I ordered the stuff and it worked out to an average of .3 of the total volume of a large dewar per day going off as gas.
The bigger dewars also have a lot of plumbing which dips into the LN2 and possibly greater vacuum loss as the tanks are bumped around and shipped.
