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Difference between isopropyl & rubbing alcohol

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February 5, 2013 3:43 PM

Folks,

 

I see references to using alcohol for stripping paint and cleaning track, etc.  There are 2 types, rubbing and isopropyl.  I am wondering what the difference between the 2 are and which type is better for both stripping paint and cleaning track.

 

Thanks,

Ed

 
 
 
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February 5, 2013 3:48 PM

Rubbing alcohol is usually 70% Isopropyl Alcohol.
For stripping paint, get the 91% Isopropyl.
 

-Keith, Michigan & Ohio Valley Lines

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mwb offline
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February 5, 2013 3:51 PM

Isopropanol is just that - isopropanol, also known as 2-propanol

 

Rubbing alcohol is generally 70% isopropanol although I have seen 90% available.  The remainder is generally water, and perhaps scents and colorants.

 

No, no, no....  You obviously have not been paying attention to what I'm about to tell you...

 
 
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February 5, 2013 6:13 PM

Rubbing alcohol, or isopropyl alcohol, typically is 70% alcohol and 30% water, and it also is available as 91% alcohol/9% water, which is why it doesn't burn. Denatured alcohol has no water in it, which is why it does burn. I use 91% rubbing alcohol as a wetting agent, in a spray bottle, for use in scenery-making because it evaporates fairly quickly vs. the water/detergent wetting method (which sometimes takes days). For track cleaning fluid on an RL LInes foam roller track cleaning car I use denatured alcohol. I've not used the 91% for stripping paint.  I also use 91% alcohol to lower the freezing temperature of windshield washer fluid.    Phil

 
Last edited by mtnhi7 February 5, 2013 6:20 PM
 
 
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February 5, 2013 7:40 PM

True, denatured alcohol does not have water in it ... but denatured alcohol is significantly different.  It it ethyl alcohol (2 carbon atoms) rather than isopropyl alcohol (3 carbon atoms).  Further, it is "denatured" with a few percent of other alcohols or solvents to render it undrinkable.

 
 
 
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February 5, 2013 7:45 PM

Originally Posted by dwp425:

True, denatured alcohol does not have water in it ... but denatured alcohol is significantly different.  It it ethyl alcohol (2 carbon atoms) rather than isopropyl alcohol (3 carbon atoms).  Further, it is "denatured" with a few percent of other alcohols or solvents to render it undrinkable.

Ethanol and denatured ethanol both contain water, Ethanol when distilled forms a positive azeotrope and contains at least 4.73% water by weight.

Isopropyl alcohol also forms an azeotope with water. 

http://en.wikipedia.org/wiki/Azeotrope

 

 Charlie

South Jersey

 

 

 
 
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February 5, 2013 8:01 PM

Rubbing alcohol means that it is alcohol that is meant to be applied topically (on the skin).   It has nothing to do with the chemical composition of the compound.  You can find/buy "rubbing alcohol" that is ethanol based.  Most rubbing alcohols are based on isopropyl alcohol probably because it's cheaper.  

 

Denatured means that the alcohol is unfit for ingestion.  Some alcohols like methanol (aka wood alcohol) are "naturally" denatured because of their toxicity.  Isopropyl isn't nearly as toxic and has additives to make it less appealing.  Ethanol is what is in liqueur and it has the most additives to a) render it less appealing and b) to get an exemption from the drinking tax ;-)

 

The ratio of alcohol to water in % or proof (%/2) affects the flammability.  91% is extremely flammable and even the 70% stuff has a low flash point, 70 degrees.  91% only drops that down to 63 degrees.

 

Quando Omni Flunkus Moritatum

 
 
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February 5, 2013 10:50 PM

Alcohol is very hygroscopic. It is rare to find any common alcohol that is entirely free of water, because it will pick up water from the air if it is in a very pure form. 

 
 
 
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February 5, 2013 11:39 PM

I think it is unsafe to use any kind of alcohol in track cleaning cars on a layout due to the sparks that sometimes are an inevitable part of crossing switches or dirty contact rollers. I have seen regular rubbing alcohol burn to.
 
 
 
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February 6, 2013 12:03 AM

I don't use a car to clean the track.  Just the old elbow grease.  I was also looking to use alcohol to strip some old tinplate parts which is why I was looking to find out which type is better, if either one is.

 

Thanks,

Ed

 
 
 
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February 6, 2013 12:19 AM

Wow, after reading all the responses it's as clear as mud to me! Where is Bill Nye the Science Guy when you need him.

 
 
 
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February 6, 2013 3:14 AM

It is used for light weight backpacking stove fuel.

isopropyl alcohol - C3H7O

 
 
 
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isopropyl alcohol - C3H7O
 
 
 
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February 6, 2013 3:43 AM

Lets make it simple.

Isopropyl and rubbing alcohol are the same stuff.

It generally comes in 70% or 91% at drug stores.

Both 70% and 91% will burn relatively easily.

Denatured (ethanol) will burn even easier.

 
 
 
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February 6, 2013 7:45 AM

Originally Posted by Tom Blevins:

Wow, after reading all the responses it's as clear as mud to me! Where is Bill Nye the Science Guy when you need him.

As a kid I remember watching Mr Wizard.

One of his experiments was to mix alcohol and water and then soak a handkerchief in it. The handkerchief was then lit on fire.

Only the alcohol would burn leaving the handkerchief untouched.

No TV magic there. I actually tried it a home and it worked.

(and no Timmys were harmed in the experiment )

 

The natural order of things is disorder.

 
 
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February 6, 2013 9:17 AM

Re: burning handkerchiefs with Mr. Whizard.  I wonder how many kids tried that experiment with something other than alcohol 

 

A very good thing my brothers and I did not see that episode.  I just know it would have involved the fire department 

 

Ed

 
 
 
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February 6, 2013 10:22 AM

Mr. Wizard was cool but Mythbusters is like Mr. wizard on steroids!!!

 

Jerry

 

 

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February 6, 2013 10:37 AM

Does any one esle see a problem with the isopropyl alcohol molecule in TMack's post?

 
 
 
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OGR Forum Member
 
February 6, 2013 10:43 AM

Molecule looks OK, formula's off by one H

 

Quando Omni Flunkus Moritatum

 
 
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OGR Forum Member
 
February 6, 2013 11:40 AM

Great thread that shows the amazing extent of knowledge on this forum.  I knew there were electrical and mechanical gurus, now I find out there are also a bunch of chemical ones too!   

 

Yea, looks like there should be either one less H molecule or it should be H8.  I did not even notice that until Chuck brought it up.  

 
 
 
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February 6, 2013 11:52 AM

i clean my track & trains with absolute! all this talk about alcohol makes me thursty.

 
 
 
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February 6, 2013 12:02 PM

I use G&T to clean my track. The molecule looks like this: -- (And frequently, so do I afterwards.)

 

Nicole. 

Not quite dead yet.

 
 
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February 6, 2013 12:09 PM

Re cleaning with Absolute and/or G&T.  As a 2nd generation Irishman I naturally take great exception to the terrible use of good alcohol for such uses !   

 

Ed

 
 
 
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February 6, 2013 1:45 PM

Old # 7 while cleaning track!!

 

Gunny

 

Member since 9/11/2002

 
 
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