Golden Rain

[@spiderdude2099]

Rule of thumb in chemistry: Unfortunately if the chemical looks really pretty and colorful it’s likely highly toxic/carcinogenic.

[@punishedexistence]

I remember doing this one in chem class...beautiful reaction. I still have the lead iodide in a little sealed test tube. Nice to see it again!! Thanks man!

[@amosz5726]

You do some of the best narration I've seen with regards to youtube chemistry

[@mrhomescientist]

Wow thank you! I always worry I bore people with excessive detail. I appreciate the comment! :)

[@rudy5623]

@@mrhomescientist Bore?! Not at all! This is definitely the best chemistry video I've seen (and I have seen a lot) in terms of both narration and content. The disposal part of it was extremely important and I'm glad you didn't miss out on it. Thanks a ton for uploading this!

[@mrhomescientist]

@@rudy5623 thank you so much! I do like to show the whole process, so others know what to do if they try it. It's definitely very important! This one is very dangerous though, so I don't recommend trying it yourself!

[@HansLemurson]

The generally good advice applies doubly here: "Don't eat the Yellow Snow."

[@elephystry]

HansLemurson Yes, very toxic stuff.

[@israelburkett8575]

Watch out where the huskies go

[@terawattyear]

Excellent demo of the reaction. Beautiful results. Couldn't ask for more. Thanks!

[@wb5rue]

What's really cool is that you can heat it up and the Lead Iodide dissolves and the re-precipitates as it cools. You can do it over and over and over again.

[@elephystry]

wb5rue This property applies to many solutions, and is exploited in sulfur recrystallization. The hotter the toluene, the greater the solubility, so if you dissolve the sulfur in hot toluene and let it cool down, you’ll get very pure sulfur crystals.

[@RajkumarKumar-bq3fq]

​@@elephystry Namaskar ji please send two chemicals name by written 9456973008

[@lordchickenhawk]

mrhomescientist I really like the fact that you show reactions to help mitigate enviromental effects of waste disposal in your videos, such as neutralising or rendering insoluble like here. Could you do a vid on how to choose compounds likely to give the desired precipitate? For example, what sulphides would best give lead sulphide, also very insoluble?

[@mrhomescientist]

Thank you! Proper cleanup is a very big part of chemistry, and an important responsibility for the amateur especially. For lead sulfide, you'd need a soluble sulfide salt. The only ones that qualify are the group I and II sulfides, for example Na2S. Usually the more convenient way to do this, though, is to bubble hydrogen sulfide gas through your solution. One way to prepare this gas is by adding HCl to FeS. H2S is quite toxic and smelly, though, so care needs to be taken with this approach.

[@mrhomescientist]

Oh and as to how to choose compounds for these sort of things, for me at least it comes down to what I have on hand. For converting to lead carbonate in the video I could have used any soluble carbonate salt, and baking soda happens to be the easiest source of that ion. If I had to make H2S, I'd probably either use the reaction I said above or Al2S3 + H2O, because I either have these chemicals already or they can be easily made with what I do have.

[@lordchickenhawk]

mrhomescientist Thankyou MrHS. I wish I'd payed more attention at school now, so I'm going to have a read of your blog instead. I'm in the process of making a chemistry set for my daughter as they are impossible to buy now thanks to our litigious nannying social constructs. It has a Diesel Punk theme and is starting to look fairly "interbellum". It's based on the same kit I had as a kid, but back then cleanup wasn't much of a priority.

[@mrhomescientist]

lordchickenhawk Very cool! You should also check out the Benchmark Legacy Chemicals Set from HMS Beagle's webstore. It's their effort to re-create the chemistry sets of yore, and it's very good. They did a kickstarter for it that I supported, so I got all the chemicals in the set. It's a wide variety of lots of useful chemicals in smallish amounts, so disposal would be less problematic at least. Good luck with yours!

[@lordchickenhawk]

mrhomescientist Yeah, that's a beautiful set, isn't it? I have looked at these before but it's a bureaucratic nightmare getting things like that into Australia. Kid's sets in toy stores here are nerfed to the point of making science not fun but funny. My son Benjamin grew up with that crap and he said to me, "They need to stop trying to make science "FUN" for kids... teach that knowledge is power. And Scientific Knowledge is the power to harness the very elements and nature of the universe and creation." He's doing a chem degree now. I think he might be onto something.

[@mineown1861]

Just as I thought watching that rain would be cool with a nice soundtrack ... Thank you.

[@maykedeprez6288]

Thanks for this beautiful explanation of the experiment. I have a few questions. I'm a student Chemistry and I would like to do this experiment at my school. My question is how long does it take untill there are golden flakes? And could it appear faster when the solution is placed in an ice-bath?

[@wb5rue]

I did this for my kids a few weeks ago. I believe the iridescent properties of the yellow product is due to the microscopic crystals of Lead Iodide.

[@Mch1071]

I love that you show the clean up. Super important!

[@lucca439]

I went to my chemistry teacher and asked if we could do the golden rain, I still don't know why he looked at me weird and left.

[@seethetruth7427]

lucca439 same smhhhh

[@shakshivashisht1578]

Our teacher herself asked us to study golden rain experiment to perform in the lab

[@goodinfo4530]

look up golden shower on urbandictionary... bit of confusion between the two

[@RajkumarKumar-bq3fq]

​@@shakshivashisht1578 please send two chemicals name written

[@Fujiko42]

Fun fact: You can use the tip of a pencil to get some small amounts of Lead

[@piranha031091]

I'd love to try it myself. Especially, to put the warm solution of lead iodide in a vacuum flask, and let it cool down for days, to get really large crystals. Maybe even repeat the process with the obtained large crystals, to get them even larger!

[@mixolydian2010]

I did the experiment and it was as scary as it was glorious, took every precautions with the lead salts. Wonderful thanks for the video suggestion.

[@mrhomescientist]

I'm glad it worked for you! It was a bit nerve-wracking for me too, but I took extra precautions and carefully planned the experiment beforehand, so everything worked out.

[@CaptainCheezmo]

Lean makes some of the most beautiful crystals. Like Wulfenite (lead molybdite), my favourite crystalline mineral

[@AsymptoteInverse]

I wasn't expecting this to be so beautiful!

[@OmegaMolecule]

Beautiful reaction! Seen it once before but wasn't able to see closely.

[@darkbeetlebot]

GOLDEN RAAAAAIIIIN SOME STAY DRY AND OTHERS FEEL THE PAIN GOLDEN RAAAAAAAAAAIN (I'm so sorry)

[@wernerhiemer406]

And those who get missLEADed are pissed off fall in depression cut themself and need some Iodine solution or even need some snow if they still can effort that.

[@D4rrag00nXD]

Lolz 😂

[@NickMoore]

Would it be possible to make this a repeatable reaction for "table art?" Using a sealed (pressure rated) container that is alternately heated and cooled to dissolve and precipitate the lead iodide crystals? Like a Crook's Radiometer or Hand boiler it would be a cool science based conversation starter.

[@weldmaster80]

very different than a golden shower.

[@old-bitprogaming4857]

Daniel Mallett lol

[@old-bitprogaming4857]

Sleepwalk No More even more lol

[@-8_8-]

Yeah, one causes brain damage. The other is the result.

[@Keldor314]

Hmm. Lead. Nitric acid. I wonder if this reaction gave the alchemists the idea that they could convert lead to gold. Fits in with the fabled universal solvent if you imagine them thinking that something stronger than nitric acid would make real gold instead of a lookalike.

[@antrax607]

That's why it's called as fool's gold

[@Cham.fdo13]

The most beautiful reaction i've ever seen. Is this really toxic?

[@mrhomescientist]

Chamme Fdz Very! All soluble lead salts are very dangerous, so I took extra care when performing this experiment.

[@xxlittlequeensxx8899]

So....a summary of your explanation. 1) We bring small amounts of Lead Nitrate and Potassium Iodide. 2) We mix each with distilled water(correct me if I'm wrong) 3) Then....um...we mix them both together as a yellow substance appears....we shake the flask a bit until dissolved. I don't know....you can correct me...or write the summary of it. I'm really being confused of what to put into, since the explanations are a bit different from each other. :(

[@TheRandomness707]

It'd be great if you revisited your chemical traffic light experiment.

[@SpaceXtract]

Stunning! Great demo, thanks for doing this!

[@Skipperj]

That was an awesome video! Thanks.....nice music as well ,quite fitting ...At one time,I was going to make a slide show/or video,with nice music,of all types of chemical reactions and observations like yours.Then I would try to book a restaurant or similar venue to show it.I think it's still possible,but it would have to be advertised properly,through chem lab people and schools,universities.

[@mrhomescientist]

Clifton Jamison Thanks! That sounds like an awesome idea. Would be cool to have that going and be serving some of that crazy 'molecular gastronomy' food!

[@trustthewater]

+Clifton Jamison I always wanted to start a science themed restaurant. Table wear made from lab equipment. Serve "out there" type foods like the molecular gastronomy stuff along with things you don see in your area. Things that people in this country wouldn't know the name of.

[@NathanandIsaac]

that is crazy how it just vanishes like that

[@rxspberry7916]

the blur makes it look better

[@saminamajid8185]

i done this experiment & i have powder form not metal. please advise me

[@xxlittlequeensxx8899]

So...what's that? On.. 0:54 Is it water mixed with both solutions or...? And....how much time did it take with you for it to precipitate? I'll be doing this in the Science fair so I don't want to be embarrassed...hahah :)

[@666Noite]

incrível reação do começo ao fim

[@pohruixin5039]

Happy new year Notite Escura 2015

[@Mylitla]

Did this in 7th grade science class. Yes, back in the day even 7th graders were allowed to handle lead salts and Bunsen burners even.

[@danielchoi4490]

Mylitla Bunsen burners are still a thing. Not as many toxic chemicals thankfully but I can't believe Bunsen burners are still a thing adults let 13 year olds handle.

[@Zeynep-mt2hq]

So beautiful, hope we will do this tomorrow at lab

[@Anil_Kumar520]

Extremely beautiful.No words to say

[@Paganforge]

This is just one of the many reasons I love science.

[@ZippieeIfy]

love this reaction. Personally I'd love to do this at home. I know most of the substances are toxic especially the HNO3(nitric acid). I'm taking Chemistry for engineers in my second semester of college so I know my way around some substances and have performed reactions before so safety in that manner is no concern. My concern would be the disposal of the lead product as regulations of drain disposal of lead is so strict that you'd be dumb to dump any of it down the drain. as far as the potassium iodide i'm sure they can be safely dumped with running water.

[@mrhomescientist]

ZippieeIfy The toxicity of nitric acid is nothing compared to the lead compounds! Also watch the video to the end - I go over disposal.

[@ZippieeIfy]

mrhomescientist oh yeah, should've specified nitric acid in a gaseous form haha. but I see now, adding sodium bicarbonate which can be safely disposed of down the drain? and the other question is what solutions did you have in the flasks at the beginning? were they just water or?

[@mrhomescientist]

ZippieeIfy I guess I don't explicitly say that, so yes it is distilled water. By "gaseous" nitric acid you probably mean nitrogen oxides, which is what the acid produces when it reacts with things, and yes those are definitely no fun to be around. Using bicarbonate turns the lead compounds into very insoluble carbonates, which I then filter off and dispose of the filter paper as normal garbage.

[@huynguyen-se6pn]

I wish I could do such an amazing experiment in my school :(

[@rudy5623]

I feel you bro

[@PauloConstantino167]

Why havent you made any more videos lately?

[@blubb7711]

Very cool, i tried it befor, but it wasn't so good... I have a idea for your next Video: Making Leadbrass I made a little pieace of it, but my burne can't handle more than a few grams. It is very hard and can even screatch steel! I had a 50/50 ratio of copper and Soldering wire, which isn't just lead, there is also tin and other stuff.

[@penguinpenguin5865]

please give me advice for thats chemistry using to plastic color,im hev industry recycle plastic. i want making pellets plastic so i wanna get formula from yours to change any color to transparent color

[@tanviarya1974]

Can you tell me that how your precipitate dissolved so fast

[@CollegeChemistry]

I am looking to repeat the Golden Rain experiment but I had a few concerns before I perform this. If you could give your input I would greatly appreciate it. 1. I understand the need for Nitric Acid, and I've seen others use sulfuric, but I have no ready access to either at the moment. Could I use HCl instead, or maybe Citric Acid? 2. You said in the video that Lead Carbonate can be disposed of as if you were to throw away regular garbage. Do you mean that this can simply be thrown out with other everyday solids/foodstuffs?

[@mrhomescientist]

1. I've always heard nitric used in this context, but I imagine any strong acid should work. Nitric is probably specified so as to not introduce extra ions. 2. Correct. Now that it's an insoluble form, it's much safer and can be disposed of in normal trash.

[@CollegeChemistry]

Thank you very much! I may try some HCl, or I may just use a slight excess of water.. I am not sure lol. I plan to get a really nice shot of the gold falling down with some snow behind it (As it should snow tomorrow)

[@mrhomescientist]

College Chemistry Nice! Be careful with the lead!

[@tasmansetter9693]

Hi Dan. Fantastic video! I am definitely going to have to try this myself. Do you need to use Nitric Acid to acidify the Pb(NO3)2 solution or can you use another mineral acid? Thanks.

[@mrhomescientist]

Well yes and no. You couldn't use sulfuric since lead sulfate is very insoluble, so you'd get more precipitation! Hydrochloric should work since lead chloride is pretty soluble, though. All the writeups I've seen for this use nitric, so that's what I went with. Doesn't introduce extra ions, I suppose.

[@Hailexx]

If you re-heat the solution, would that reset the experiment? Could you get it to rain over and over again by heating it up and cooling it down?

[@mrhomescientist]

Yep!

[@marsmunky]

This is not to be confused with a golden shower.

[@fegolem]

Beautiful! If convection could be minimized, would the Lead Iodide form larger / thicker crystals? Would thicker crystals also be golden?

[@mrhomescientist]

Yes, the slower the cooling the larger the crystals will grow. This is true of any crystallization operation, and as an added benefit it also ensures high purity. Large crystals of lead iodide should be just as golden as the small ones!

[@theginginator1488]

The lead iodide might dissolve again from the nitric acid you added

[@mrhomescientist]

+TheGinginator14 Don't worry, it won't. It will dissolve any oxides or carbonates, but otherwise there's no reaction there.

[@Mast6r90]

This is gorgeous, great video.

[@simonhummer2465]

You said that you were adding a hot sodium bicarbonate solution to everything that came in contact with the lead, didn't you have problems with the sodium bicarbonate decomposing into sodium carbonate or is that even intended?

[@mrhomescientist]

I did notice some bubbling from it, so you're probably right and it did decompose a bit. That doesn't matter here though, because the carbonate ion remains intact, and that's what "sequesters" the lead into the insoluble lead carbonate.

[@LATownsRS]

Would you be able to keep it in the flask as something you can look at or shake around every now and then like a little snow globe?

[@mrhomescientist]

+LATownsRS Sure!

[@velmegreenidge4326]

I did this experiment at school today ,it was soooo cool

[@shmaras]

Would it be possible to make a lava lamp style rig, which would cycle and heat up the solution until clear then cool to allow gold rain.

[@mrhomescientist]

I definitely think so! I had that idea quite a while back. The key would be to find a compound that has a very steep solubility curve, so you don't need a huge temperature differential between the top and bottom of the lamp. I think it's definitely doable though.

[@TroyFoxxin]

mrhomescientist I kinda think i know a design that would allot that to happen. using a smart board on a timer which can also drive some LED for advance effects if you wanted to watch it in the dark. But can build a stand based on like your hot plate. but built to fit the base of whatever holds the solution. and thanks to how long it last can program it to heat and cool the solution before you normally wake up. Then enjoy it for a good portion of the day or program it the right time guest come over so can show it off. Kinda wanna build the base of one now. but i most likely wont. im sure don't want to risk something like this falling over in a RV during travel and it break all over the floor. lol

[@mrhomescientist]

Troy Foxxin Yeah certainly not a lead solution! That's gotta be securely positioned. I thought peltier elements would be a great way to heat and cool the display - small and efficient.

[@shmaras]

mrhomescientist you could even reverse the polarity to aid in the cooling process, might even produce cool effects if cooled to quickly.

[@squimball]

Was wondering if you were still alive. Great vid as always!

[@Airsoftpsyco1423]

How does the density and melting point of this lead iodide compare to that of gold or a gold alloy? Seems like a great way to "doop" people into buying fake gold, if it doesn't happen already!

[@mrhomescientist]

They aren't even close. Really the only similarity is in the color, and even that is a bit iffy if you know what you're looking for! Could be used as one of those $5 gold leaf bottles they sell at souvenir shops, maybe. Keep an eye out! :)

[@taduyquynh1943]

Hello. Can I use sodium iodide instead of portasium iodide?. I can't find potassium iodide in my school's lab. HELP

[@mrhomescientist]

+quynh taduy Any iodide salt should work, yes. Any soluble lead salt too, for that matter. I'm surprised your school's lab has lead compounds! Be very careful if you do this experiment, and be sure to pay extra attention to safety and disposal. Lead salts are highly toxic.

[@soundouss3354]

?Did the experiment work if replaced lead nitrate silver nitrate? And what is the time it took this experience in order to succeed

[@mrhomescientist]

No. Making lead iodide requires a lead compound.

[@x.p.3574]

what would happen if the first to led substances where added differently, the one poured into the other, would it react differently?

[@mrhomescientist]

X. P. The order doesn't matter - lead iodide is always produced. I did it the way I did to avoid handling and pouring the toxic lead nitrate solution as much as possible.

[@BitsAsLiga]

Can you use acetic acid instead of nitric acid

[@cloudiva568]

Can i use your video to translate into my language

[@abhinavtonde4460]

How much does it take to get start to crystalize ?

[@Roham]

Great video! Instant urge to go buy a chemistry set!

[@kelpsie]

If you re-heated the solution with the crystals still inside, would you be able to re-produce the precipitation indefinitely?

[@mrhomescientist]

Yes that should work! It's just repeated recrystallizations, really.

[@ducruto]

I did this myself, and I was wondering why my solution turned brownish-amber after heating? Thanks.

[@mrhomescientist]

How pure were your reagents? Sounds like you oxidized some KI into iodine.

[@AM0mentOfScience]

Your video inspired me to search "Golden Rain" in the Googles... TIL: the returns from RedTube *are NOT* related to potassium iodide and lead nitrate. :) All kidding aside, great video. Should definitely revisit this when you do get your new camera.

[@ElCapitanDudeMan]

I'm guessing that once this process is done, you have to whip up a whole new batch to get the same thing again? Is there any way to clear it up and get the same result with the existing solution?

[@mrhomescientist]

+Michael White Sure, simply reheat the solution to near boiling and the lead iodide will redissolve. Upon cooling, the same crystals come back out of solution.

[@JosephDunfee1978]

Can you show me how to make gold rain

[@hello_world777]

what a great video and experiment! I really enjoy your vids! please, keep doing cool chem stuff and upload!

[@hyonii9960]

It's really gorgeous 😍

[@saminamajid8185]

i have powder ppt .please help me

[@benjaminandersen1097]

golden rain huh.. sure is prettier than a golden shower

[@weldmaster80]

Depends on how well hydrated they are lol

[@Hellspawn4u]

make a dimond rain

[@kiwi_banan_]

What happen with KNO3 in this solute,when we heated it?

[@mrhomescientist]

Nothing. It stays in solution.

[@CHOCOLATETHUNDDAA]

What can you use lead iodide for?

[@YoungCine]

Hi, what kind of reaction is this? A synthesis or a double replacement ?

[@mrhomescientist]

This would be double replacement, or a precipitation reaction. Check out the link in the description for a writeup!

[@YoungCine]

mrhomescientist thanks and will do!

[@rayadamsii6057]

is sodium hydroxide a nitric acid somehow?

[@freeringer]

Is it possible to melt the lead iodide into a bead or something

[@mrhomescientist]

Wiki says its melting point is 402 C, but I suspect it would decompose before that.

[@-Cryptic-67]

why do i feel like when he pee's he is like 'ooh what a beautiful yellow'

[@flashdemonic5576]

Because you like to imagine men pissing.

[@wakimaniac]

Golden Shower. (If you know what I mean)

[@thatsmellysmellthatsmellss5313]

How long did it take for the solution to cool down?

[@amandayang19]

I have a question. Does it matter how much distilled water is used with the same amount of potassium iodide and lead nitrate that you used in the video?

[@mrhomescientist]

Amanda Yang I suppose you could calculate exactly how much water is needed for saturation at 100C and only use that much. I forget if I did that for the video! Shouldn't make too much difference besides the time needed to heat up and cool down the solution.

[@amandayang19]

Alright, thank you! I appreciate the demonstration by the way!

[@dragojustin2580]

mrhomescientist were do you get your materials I cannot find a good source for chemicals.

[@mrhomescientist]

eBay is a surprisingly good source. For this video I bought my KI from there, and made the lead nitrate from lead metal (from eBay) and nitric acid (which I made from instant cold packs and drain cleaner acid).

[@dragojustin2580]

Thank you very much for this advice I can't wait for more videos like these!

[@henrikwong9545]

How long does this experiment last for?

[@PenguinzAreAwesome]

Where do you get all of your glassware/reagents? I've always wanted to get into hobby chemistry

[@mrhomescientist]

Brian Glazier eBay is a surprisingly good source for just about everything. You also learn to become a compulsive label reader - whenever I see a bottle in a store, I check to see if there's anything useful inside!

[@rainbowchickens8415]

mrhomescientist That's exactly what I do haha, I always check label's for anything useful :D

[@AtomicFire41]

Science has done it, we've turned lead into gold

[@-8_8-]

You know I wonder if this is where the idea came from that it could be done. Someone spills some on a block of lead and sees yellow?

[@niurkaguillen]

Hi! Can I use acetate lead to support of nitrate lead?

[@mrhomescientist]

Niurka Guillen Sure, any soluble lead salt should work.

[@MrPoffersher]

Awesome demo.

[@SeungCanFade]

How long would a solution last in a container like a mason jar?

[@mrhomescientist]

Seung Choe Should be indefinite. It's a stable compound. I could see the crystals breaking and getting smaller if you shake it, but that could be fixed by heating it up again to dissolve. Just don't drop the jar!

[@SeungCanFade]

Thank you for the response! It looked so pretty, that I considered making an art installation with it. However sourcing some of the chemicals have been challenging haha. I do have a few questions, if you don't mind. Does the 'Golden Rain' occur due to the solution being super saturated? Knowing the saturation point at various temps, could we have the lead dissolve and precipitate out at temperatures closer to room temp? Although I assume that the effect would be noticably diminished. I want to create a wind chime, but also include sealed tubes of the solution. I was thinking of creating a solution at near saturation point for ~70F in hopes that maybe the solution heats up and dissolves in sunlight, but precipitate out when it cools during the afternoon.

[@rawannabout5354]

Thank you 😊 it's very beautiful experiment

[@CoOzEbOy1]

What can be done with the bottle of lead iodine?

[@mrhomescientist]

Lead iodide used to be used as a yellow pigment, but being rather toxic it isn't used for that any more. For me it's really just a neat display piece that looks like gold, but isn't!

[@abheyshankar143]

Chemistry and enthusiasm are analogous terms- I must say-Ayush Shankar

[@PekWen]

how long does it takes to cool down?

[@KowboyUSA]

I'm not sure this is what my wife had in mind when she requested a golden rain shower...

[@Currs869]

The question is can this be considered a GOLD??? has anyone performed a lab test on it's authencity...

[@mrhomescientist]

It's not gold, it's just golden colored. The compound is lead iodide.

[@x9x9x9x9x9]

That is so damn pretty.

[@explosionspancakes]

Alchemy at its finest.

[@akhilthechemist]

Where did you get lead nitrate and potassium iodide

[@mrhomescientist]

Akhil the Chemist I made the lead nitrate myself and bought the KI on eBay.

[@akhilthechemist]

mrhomescientist where did you get nitric acid and lead

[@mrhomescientist]

Akhil the Chemist I made the nitric acid myself and bought the lead on eBay.

[@mrkvaccc]

So freaking awesome! Thumbs up!

[@Cheeseboat20]

What a beautiful video.

[@adamstorey8825]

I tried this experiment and my Lead nitrate solution won't clear up. it stays cloudy. I tried warming it up but nothing works. any ideas?

[@mrhomescientist]

Adam Storey As I mentioned in the video, lead nitrate has a tendency to hydrolyze to insoluble products. A very small amount of nitric acid should clear it up.

[@adamstorey8825]

mrhomescientist. could I use HCl?

[@mrhomescientist]

Probably just about any acid would work, but I imagine they always recommend nitric so as not to introduce extra ions. I'd try it on a small sample first in case something goes awry.

[@adamstorey8825]

mrhomescientist ok. I also didn't use distilled water. I used tap

[@mrhomescientist]

Adam Storey Well there's your problem! :) Distilled water is very important to avoid weird problems like that. Science is all about eliminating variables!