Buying a hot plate magnetic stirrer-what do I need to know?

[Kirk Gittings]

I won't be using this much-mainly to mix up my film developer batch a couple of times a year. So I want to do this cheap-probably used off the bay. I know nothing about them-so I could use some sage advice.

[Ken Lee]

I have an old but working magnetic stirrer (non hot plate) which you can have for the cost of shipping if you like.

[Colin Graham]

The heated ones are usually a lot more expensive. They're handy for some the alternative processes solutions, but not absolutely necessary for mixing typical developers and fixers. I've used a non-hot plate Thermolyne model for a dozen years, and it's perfectly adequate for most uses. Also, the straight stir-bars seem to work better than the star-shaped, which tend to fly out the magnetic field more often in the heavier saturated solutions.

But if you need a heated one, be careful of some the used models on Ebay. One of the Corning hotplate/stir units has the controls on the OEM cord, which has often been replaced on used models with a plain cord. So when it's plugged in, both the heat and stir-bar speed are on full blast. I made the mistake once of buying one of those once.

[Carl J]

I have an old but working magnetic stirrer (non hot plate) which you can have for the cost of shipping if you like.

Ken, if Kirk doesn't take it I would be interested. I'm assuming the hotplate capability isn't strictly needed.

Carl

[Ken Lee]

OK Carl :cool:

[sanking]

I would look on eBay for something like a Corning PC-320. Just do a search and you will find a number of used units for sale. If you look at a picture of one of these you will see that there are two large dials on the front of the machine. One controls rotation speed of the magnetic bars, the other controls temperature. The used units may or may not include the stirring bars but you can buy packages of these bars separately.

My unit is similar to the Corning PC-320 and I definitely find the hot plate feature useful, and if you shop carefully the feature should not add a lot of cost.

Sandy

[Bill_1856]

I never heard of a hotplate stirrer. What is it, and why would one use it instead of a plain stirrer?

[Jim Noel]

Some chemicals mix more easily at temperatures above normal working temps, thus the heated plates are a luxury.

[Jim C.]

I never heard of a hotplate stirrer. What is it, and why would one use it instead of a plain stirrer?

A hot plate stirrer will keep your solution at a determined temp as opposed to just a plain stirrer which will cool down
your solution.

Kirk, buy new, a lot of the units on eBay are EOL units with no spare parts available, and of dubious lineage
I picked one up myself used and it was a headache to replace parts. I don't even use it any more,
there are inexpensive new one's available on the auction site in the $100 - $200 range.

[Peter De Smidt]

Randy Moe posted about a new one that looked good a couple of months ago. A search should bring it up.

[Vaughn]

I have used non-heating magnetic stirrers for a long time -- wonderful devises. I bought non-heating ones for the university darkroom because I knew eventually a student would leave the heat on...and generally not needed much. A water bath in the sink to bump up the temp occasionally works well -- especially with SS mixing containers.

One safety caution, tho not super critical...the platform of the stirrer should be large enough so none of the container hangs over the edge (basically decreases the chance of knocking it off.)

[Colin Graham]

A hot plate stirrer will keep your solution at a determined temp as opposed to just a plain stirrer which will cool down
your solution.


Some solutions are exothermic, meaning the simple act of mixing or dissolving certain chemicals heats the solution. For example while mixing pyrocat solution B the carbonate will get quite warm on its own.

[Tin Can]

Randy Moe posted about a new one that looked good a couple of months ago. A search should bring it up.

http://www.amazon.com/Scilogex-86143101-MS-H280-Pro-Circular-Top-Magnetic/dp/B00AYGIFCA

After purchase you can email a coupon for a very quickly delivered thermocouple probe. I think the distributor is in Texas and they answer emails for the probe immediately.

Mine works fine.

[Tin Can]

btw, don't buy the $50 rig for holding a TC, the back right has an 8mm threaded hole, 16" of metric rod and an old clamp worked for me.

[Ginette]

I won't be using this much-mainly to mix up my film developer batch a couple of times a year. So I want to do this cheap-probably used off the bay. I know nothing about them-so I could use some sage advice.

I have 2 Fisher Isotemp units, a 10x10" plate stirrer and a 7x7" hot plate stirrer.
You will find this brand easily used on eBay.

- Capacities:
The capacities of the Fisher are:
1L on 4 x 4” model
4L on 7 x 7” model
6L on 10 x 10” model
It should be similar for others brands but look carefully at the capacity before buying.

- Power cord
As a member said, be shure that you have the original cord for an hot plate stirrer.

- Vessels
You have to work with vessels that can handle heat adequatly.
If you wish to use stainless steel, you must have good quality non magnetic stainless steel unless the magnetic stirrer bar will not work correctly.

- Magnetic stirrer bar
A lot of sizes and forms are available.
Personnaly my choice is a Spinplus Cross Shape Magnetic Stir Bar 38mm

_____
Edit
I got theses 2 stainless steel beakers from Jerold here on the forum and they work nicely on the 2 stirrers
http://www.largeformatphotography.info/forum/showthread.php?110667
http://www.largeformatphotography.info/forum/showthread.php?110666

If you look at the Fisher Isotemp, be aware that they produce 120 and 240V models. They produce also an hot plate alone (no stirrer!)

[neil poulsen]

When I built my darkroom years ago, I decided one luxury I would afford myself was a magnetic stirrer. Sweet!

I purchased mine used through a scientific supply store for $150. It has both the stirrer and hot plate. If it makes any difference, it's a Markson 502R. It's worked great all these years. I imagine that it can boil water, if needed. (Tea?). It has a ceramic or porcelain layer on the hot plate that's impervious to chemicals. It can handle the weight and volume of over a gallon.

Actually, I rather like having the integrated hot plate. For example, Kodak recommends mixing at warm temperature. So, I mix on low temperature. If you ever do PT/PD, you may want to heat the developer.

Overall, it's been an excellent tool.

[Kirk Gittings]

I have an old but working magnetic stirrer (non hot plate) which you can have for the cost of shipping if you like.


Ken, if Kirk doesn't take it I would be interested. I'm assuming the hotplate capability isn't strictly needed.

Carl

Thanks so much for that offer Ken-very gracious. I think I will start looking for one that heats also as I think that feature would be a good addition for a variety of reasons to my DR too. Thanks again. Go Carl!!

[Jeff Dexheimer]

Sounds like you've made up your mind abut the hot plate type mixer. My thought is, unless you need to maintain a precise temperature or anticipate long mixing times it would be sufficient to use hot tap water with a regular magnetic mixer. Regardless, be sure you use suitable glassware for hot plate use, Pyrex comes to mind as that's what we used in my chemistry labs.

[Michael Rosenberg]

Kirk,

I have a Corning hot plate stirrer. Corning make the best/sturdiest plates, and the strongest stirrers. The stirrer is so strong you can put an insulated water bath on top to hold temperature and still be able to stir. I used them in my lab for decades and had no problem. I picked my current one up at a local university surplus store. A wonderful source of equipment. I got my lab stool and miscellaneous glassware there!

Mike

[Ginette]

Sounds like you've made up your mind abut the hot plate type mixer. My thought is, unless you need to maintain a precise temperature or anticipate long mixing times it would be sufficient to use hot tap water with a regular magnetic mixer. Regardless, be sure you use suitable glassware for hot plate use, Pyrex comes to mind as that's what we used in my chemistry labs.

Hot tap water if you have a water sediment post filter system (red housing and right filter).
Unless it is better to use an hot plate stirrer to heat the filtered water or distilled water.

[Kirk Gittings]

Hot tap water if you have a water sediment post filter system (red housing and right filter).
Unless it is better to use the hot plate to heat the filtered water.

Exactly, I don't in my darkroom-do in my kitchen but thats in another building. I use jugs of distilled water for my film development.

[Ken Lee]

Thanks so much for that offer Ken-very gracious. I think I will start looking for one that heats also as I think that feature would be a good addition for a variety of reasons to my DR too. Thanks again. Go Carl!!

Okee dokee. Carl please email PM me with your shipping address and I'll send it out after this snow storm ends.

[Duolab123]

I am a chemist so I have had to use a lot of these things over the years. The hotplate versions are not usually as good at stirring as a simple stirrer. I have a ancient Magni-stir very unimpressive to look at works great I have used it for the past 45 years. Stirrers that have the drive magnet very close to the driven stir bar work best (Kind of obvious:)) I bought a Talboys brand propeller mixer (mounted it to an old ring stand) for mixing bulk powders like XTOL, has a DC motor and a rheostat works great. I heat my RO water in a microwave and add the powder slowly. I still like Dektol and Bromophen etc. I store stock solutions in small Boston Round amber PET bottles (Freund Container online) filled to the top (no Air) So my XTOL easily keeps for a year I fill an 8 oz bottle if I want 16oz of working solution.

You need to keep an eye on the stirrers, they will over speed cavitate and suck in air that will oxidize your developer. I get my purified water as warm as allowed.
I agree the star shaped bars are no good for dissolving powders, Corning always had good products back when I was still in the lab.
Hope I helped

[Jim C.]

Some solutions are exothermic, meaning the simple act of mixing or dissolving certain chemicals heats the solution. For example while mixing pyrocat solution B the carbonate will get quite warm on its own.

Never used Pyrocat, and good to know if I ever decide to try it.

[Carl J]

Okee dokee. Carl please email PM me with your shipping address and I'll send it out after this snow storm ends.

Hi Ken,

PM sent.

Thanks. :)

[Ginette]

...
I agree the star shaped bars are no good for dissolving powders, ...


Witch form and lengh do you recommend for a 6" diameter beaker?

[Vaughn]

I did make the mistake of trying to mix gelatin with water using the Corning magnetic stirrer (at about 12% and 68 F). I eventually I had to go to a hand stirring stick as the the bar would no longer spin as the gelatin thickened!

The bars I have used have been about an inch to 1.5 inch. I'd pour the Dektol or D-76 or HCA powder into the spinning water, then take a stirring rod/paddle and get the water moving in the opposite direction. When the bar would get the water moving in the proper direction again, all the powder would lift off the bottom edge and mix in nicely. For 20 years, I mixed probably an average of 200 gallons of chemistry, a gallon at a time, over the course of a semester. For the ten years before that, include perhaps a hundred gallons of powdered fixer...all by hand (stirring rod). Boy was I glad to get the magnetic stirrer and go to liquid Rapid Fix!

[Colin Graham]

Ha yeah I tried that too once. For carbon a mag stirrer is still useful for mixing the pigment dilution before adding it to the glop. Especially pigment pastes or tube watercolors which take a while to disperse.

[Vaughn]

I use it as a way to stir the glop right before pouring -- the magnetic stirrer does a good job without adding air into the glop.

[Chauncey Walden]

Kirk, I have a 8 inch heavy duty non-heating lab stirrer and I got a whole set of rods of different lengths for it up to about 2.5 inches. If I'm using the Rubbermaid 6 liter tub I just move the tub around in a large circle on the base to bring the stirrer to all areas of the bottom. That way you don't have to use so high a speed that so much air is sucked into the mix.

[Kirk Gittings]

thanks Chauncey. Good advice.