Rochelle Salt

Piezoelectricity is the charge that accumulates in solid materials in response to applied mechanical stress. Substances that exhibit piezoelectric properties to a greater or lesser extent are crystals (Tourmaline, Quartz, Topaz, Rochelle salt and sugar cane), certain ceramics and biological matter such as bone, DNA and various proteins. Quartz and Rochelle salt exhibit the greatest amount of piezoelectrical properties and since the ingredients and instructions for making Rochelle salt are relatively straightforward I decided to make some to play with. I found some helpful guides here and here, but diverged from both guides several times without ill effect. Here are my instructions for making Rochelle salt (Potassium Sodium Tartrate), which yielded at least 5 tablespoons full of the salt and several large single crystals in a few days.

I've recorded two mechanical force tests of a single crystal using both a digital and analog oscilloscope here.

Step 1 Making Washing Soda

The recipe calls for cream of tartar (Potassium Bitartrate or Potassium Hydrogen Tartrate) and washing soda (soda ash or Sodium Carbonate). Cream of tartar is a byproduct of winemaking; as the grapes age this acidic salt forms on the barrels of wine and is collected and used in a variety of household purposes, from preventing sugars from crystallizing to an ingredient in baking powder to stabilizing egg whites in recipes. Washing soda is highly alkaline (pH of 11) and often used as a water softener. It can be extracted from the ashes of plants and is sometimes used to make German pretzels. Washing soda can be made by heating baking soda (Sodium Bicarbonate or Sodium Hydrogen Carbonate) in an oven to break and evaporate the bonds of hydrogen to leave the Sodium Carbonate.

Comments

[2xlbu4u]

Whoa.. I was just thinking that It's so inexpensive to make. What if you were to create a large slab and place it in-between 2 concrete slabs the size of a single lane highway. You could put small grooves in the top slab to induce vibration as cars passed over it (like a rumble strip). Make enough for at least a ¼ mile and wire them up in series / parallel (figure out what will give max power). Anybody know why this won’t work ? Maybe the useful life of the crystal is too low and it will just shatter after a short time. If that is the case, maybe you could introduce an inert polymer into it to maintain structural integrity. Gosh if only I didn’t have a day job and limited funds or I’d be trying it right now L

[emdaniels]

That would be pretty cool! Unfortunately it's really brittle so it would most likely break from the pressure. You'd probably want to sandwich it between sheets of conductive foam to cushion it and catch the electricity generated. You should try it!

[lookwhatjoeysmaking]

my mother wants to know if you color Rochelle Salt if you added food coloring? anyone know?

[emdaniels]

Haven't tried with food coloring yet! A quick search of google doesn't come up with a lot of info for it either.

[EngineeringShock]

Congratulations on your win! I'm front Ottawa as well =)

[emdaniels]

Thanks! You should come to the Mod Lab maker meetups at Artengine! Great group of people there. :)

[lookwhatjoeysmaking]

i tryed makeing some using collins video but it stoped fizing and it wasnt cleer it was yellowy color any idea why?

[emdaniels]

Regarding the yellow color, I might start by checking the purity of the cream of tartar. There are some manufacturers that sell cream of tartar with filler to reduce costs. I heard that McCormick brand sells a good cream of tartar, but I haven't tested it.

[lookwhatjoeysmaking]

cool thank you for the speedy reply.

[inspecter gadget]

Brilliant ! have not come across this compound before, even though I have experience in crystal growing -much [ trial and error]:-)

Your recipe is very reliable, I do however have a ? Washing soda [na2co3.10h20] is a very accessible chem. Your calcination? method is logical but energy dependant? Na2Co3 has an R.A.M of 106.0 the decahydrate is 286.0 =[2.7]

if you use same proportions but use same scoop for both chems it work out well

Apologies if I am Saying what you are already aware of:-0

[emdaniels]

Thanks inspector gadget! It's true- both will work out well. I didn't have access to the Arm & Hammer Washing Soda or any other decahydrate washing soda from a store so I had to make my own. If you can buy washing soda and want to skip the steps of making it yourself it should still work out fine.

[inspecter gadget]

I Made Far Too Much Of The Stuff Then I Needed -But With Selective Growing There The Size Of Alum Crystals.

[Kiteman]

I'd like to see how you mount or connect these crystals to actually tap into the voltage generated.

[emdaniels]

I just added two mechanical force tests of a single crystal using both a digital and analog oscilloscope to my website: http://www.emilydaniels.com/2011/11/further-testing-of-rochelle-salt/

[Kiteman]

Cool.

[PierreF]

Hi! I tried some time ago to make a speaker out of this:
http://www.youtube.com/watch?v=nRFgY4_3lHU

And it worked pretty well :)

[emdaniels]

Nice! Thanks for sharing!

[kcdoodle]

wow. This has my head buzzing! Could you make a mini-alternator type generator, like to recharge a small battery for a little radio, or cell phone by putting many small crystals on a wire, and a wheel at equal distances, turn a crank to strike the crystals against a flywheel, to run electrical appliances? How about LED lights? Many options here!

[wkoepp]

yes with some imagination you can construct the things listed. Just keep in mind your results might not be what you expect. Even though stated on this instructable that a crystal could put off 9V it would take a large crystal with a large stressor. there is a reason why these crystal are typically used as sensors allot. The voltage output is too small to run a load but high enough for accurate readings. You might want to look into using it in combination with a BEAM Robotics project.
Hope your ideas are a success though and have fun.

[Broom]

Actually, the voltage output is high enough - 9.6 V is more than any USB-powered device uses! It's the current output that's too low to be useful (or, ultimately, the power).

[wkoepp]

Well the voltage out put is roughly 9.5V peak-to-peak AC shown is studies, so the actual rms value (DC volt equalent) will be 70.7% of that of one peak. one peak being 4.25 V max assuming this is a sine wave AC output. The voltage rms there for is 3.35V. This is less than the 5Vdc output of a USB cord. As for current you will need to determine the internal resistance of the crystal as well load resistance apply the total resistance into the ohms law formula and that will give you your current. the crystal itself creates a potentual difference (voltage) not current. you must have a complete circuit to have current.

[wkoepp]

I wanted to add though that the use of a piezoelectric crystal as a energy source would be good in a BEAM application using a Miller Solar Engine or other similar engine, just replace the solar cell with the crystal. In this fashion you should be able to store up the needed energy to run a load. Experiment and Explore! :)

[Broom]

Thanks for the correction, wkoepp, and your point about piezos as a Miller Solar Engine power source made me wonder about their usefulness for energy storage.

And I'm not the only one! This study suggests efficiency can be as high as 95%!!! Wow!
http://adsabs.harvard.edu/abs/1984PhDT.........9E

I wonder what the volumetric capacity of piezos is like... Can't find anything in a quick google.

[sharp8874]

ok so i've tried to do this twice using half of everthing and all i get is a pot of slushish stuff. Any idea of what im doing wrong?

[jedi453]

Is the slushy stuff like a soft thing that covers the whole pan, leaving no liquid behind? If so I had the same exact problem. According to one of the listed sources for this experiment, there is a Cream of Tartar substitute that is often labeled as "Cream of Tartar" while it's not Potassium Bitartrate, which is what is needed for this experiment ( real Cream of Tartar ) . It appears that this is the result of using the substitute, because when I redid the experiment, doing almost the exact same thing, but with more expensive/different cream of tartar and it worked perfect...
Make sure to buy the more expensive cream of tartar and look at the label and see if it says anything about wine. If it is from a wine distillery or wine making place, it should be the real thing.
But just to be clear, if you added too much washing soda ( as in you kept adding it even when the solution didn't bubble when it was added ), then that could have easily caused a problem too...
Good luck, I hope it works out,
Jedi453

[mrshr3d]

I had the same problem. It has still formed the Rochelle Salt crystals but they are just very tiny. I have a feeling this is due to contamination of putting too much soda at the very end, as I noticed by solution was not 100% clear at the very end, but had stopped fizzing. To fix it, I drained off the excess water, added a bit of water (maybe only half a cup approx) and reheated and melted the "slush" (Melting point of Rochelle Salt being 75C/176F). Solution was clear and formed larger crystals. I believe you can achieve even better results/larger crystals if you use distilled water rather than tap water.

[sharp8874]

ok! thanks so much! im going to try and do this again today with full amounts and distilled water.

[emdaniels]

The pot of slushish stuff is after you take it off the stove or after you've cooled it in the refrigerator?

[sharp8874]

after i've cooled it in the refrigerator

[emdaniels]

There was some adjustment of measurements in the recipe- when you were adding the washing soda to the solution did you notice an abrupt end to the bubbling after a time? It may be that you should try the recipe with the full amounts instead of half. Hope this helps-

[jedi453]

This project looks like a lot of fun, and I definitely want to try it, but since I don't have anything to measure grams and I live in the U.S. I'm forced to use measuring devices that measure units like teaspoons, tablespoons, ounces and Cups. I want to thank you for providing approximate measures in those units, but as I looked over the conversions you gave they didn't make sense to me. To be sure I used Wolfram Alpha ( wolframalpha.com ) to check the measurements. According to it, 250 grams of sodium bicarbonate ( Baking soda) is about 23.5 teaspoons ( ~25 teaspoons ), whereas you said it was about 25 tablespoons. The same applies for the Cream of Tartar, 100 grams of it should be about 10.4 teaspoons ( Where you wrote 10 tablespoons ). I don't mean to nit-pick but if I'm right the Factor of 3 would probably mess up the experiment. If I am right, I urge you to fix this guide by switching tablespoons to teaspoons for these measurements. Thanks again for the guide. I hope this helps, I'll try to double check the conversions. Just in case I'm right, remember Tablespoons are represented as Tbsp and Teaspoons are represented as Tsp. Also 3 Teaspoons is equivalent to 1 Tablespoons, so the difference is a factor of 3, thus why I wanted to be sure. Please correct me if I'm wrong.
Hope this helps, and thanks again,
Jedi453

[emdaniels]

Thanks for your research into this! I'm actually an American living in Canada and grew up using the imperial system but have since needed to adapt to the metric system. I'll adjust the recipe since I made it by tablespoons and teaspoons.

[jedi453]

Thanks for the reply and for changing the Instructable. I'm happy to say I just finished all the main work and just put the pan in my refrigerator!
I did some double checking on what I found on wolfram alpha.  After finding I could get about 4 Tablespoons of Cream of Tartar from a 42 gram bottle, I realized that Wolfram Alpha must be assuming it's in a pure single crystal, or completely compressed.  So it is very possible that the Cream of Tartar you would buy at a grocery store would be about 100 grams for 10 Tablespoons.  I'm sure there's a similar set of circumstances with the Baking soda. I'm sorry to have "corrected" your statements that were probably already correct.  In retrospect however, my mistake shows that these quantities should probably be represented in either units of volume or units of mass, but not both.  This is just because the density is not really fixed.
Just in case it helps:
 - 10 Tablespoons is about 150 mL
 - 25 Tablespoons is about 370 mL
 - 1 Cup is about 267 ( ~ 270 ) mL
The way I've been doing these conversions is with Wolfram Alpha ( again wolframalpha.com ). To convert one unit of measure to another, just type "(amount) (unit of measure you're converting from) in ( unit of measure you're converting to )". Of course replacing things as necessary.  This works with mass as well, assuming STP, for example I used something like "100 grams of cream of tartar in tablespoons" as a search earlier to check the units. Again keep in mind with mass to volume conversion (and vice-versa) a certain ( possibly unattainable/unrealistic, at least in the kitchen ) density is assumed, as I just found out.
Thanks again for your awesome Instructable and taking my advice,
Jedi453

[zeeproduction]

I can understand the struggle you're passing through because I do this all stuff in reverse. First of all I strongly recommend you this site: http://www.onlineconversion.com and then just one opinion, m, g, Kg, l, cubic cl, cubic meter, Km, tone, Kg force everything speaks the same language and not only it's an international measuring system so I think it would be a good idea to go buy a metric ruller (as a citisen of planet Earth) and to start using it or perhaps, why not, even teach you kids to know what a cm or Km is. Once again is just my opinion. Good luck and by the way very interesting tutorial.

[jedi453]

Hi zeeproduction,
Thanks for the suggestions and the link. Don't worry, I already have a metric ruler and have used the metric system many times before. I just don't have any really direct approach to measure mass in grams. I was just trying to double check that the measurements were correct.
The instructable originally had approximate measurements in tablespoons and grams. The numbers didn't seem to correlate to me, so I just wanted to double check them. I find that Wolfram Alpha is more than enough for me when converting units, it's just that if the units aren't of the same type, it makes assumptions on the relationships between the types. In this case, when I tried to convert grams to tablespoons, since the gram is a unit of mass and the tablespoon is a unit of volume, it made an assumption about the density of the chemical in question. This problem does not occur for converting between units measuring the same type of quantity.
Thanks again, Jedi453

[zeeproduction]

Wow, that's a nice thing. If it is so it's really cool. And you're right. Anyway I have the same syndrome when reading fl and oz ;)). And I agree, for this experiment to have a nice rate of success it needs quantities expressed in a accurate manner. But I realy enjoyed this one and hopefully one day I'll give it a try.

[emdaniels]

Here the cream of tartar comes in 67g tins, and the slightly annoying part is that I used about 1 and 3/4 tins to make the rochelle salt, so I'm guestimating that it was 10 but I'm not sure exactly. The more important part is getting the ratio of cream of tartar to washing soda right as there is a marked difference when the solution reaches it's saturation point, so as long as you are watching it and adding enough spoonfuls of the washing soda it should turn out ok. Thanks again for your conversions!

[makincoolstuff]

is it possible, using a spring loaded piece of steel, to create a spark like in a peizo electric barbecue igniter.

[emdaniels]

Yes I would say so.

[ctaus]

I'm wondering... Can these be dyed or tinted as they grow? I'm thinking possibly paste frosting tint, tho I'm not sure how the sugar would affect the growing process