Can you give me an explaination of the term "CNHM" as used to describe
some kind of unit of measure.  Possibly an ammount of contamination
allowed.

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Request for Question Clarification by markj-ga on 27 Sep 2004 13:54 PDT

ufi911 --

Based on your reference to "contamination," one possibility for the
meaning of CNHM that interests you is its use as the general chemical
formula representing hydrocarbons.  In this context it would usually
look like this -- "CnHm".

I have found online references to measurements of "CnHm" as a slight
xontaminant in some industrial products like liquid nitrogen,
"99.9%pure" hydrogen, and others.

Does this description sound right to you?  If so, is there anything
else you need to know?

markj-ga

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Clarification of Question by ufi911-ga on 29 Sep 2004 09:06 PDT

Markj
-

It appears you are on the right track.

Can you help me with what CnHm actually is?  It appears to be an
allowable amount of a gas mixture that is NOT the actual gas being
measured.

So is it a specific material (gas?) or is it 'everything else' that isn't the gas?

I hope that makes sense.

Thanks,

-John

ufi911 --

Thanks for your clarification.  I am not a chemist, but I am confident
that I can give you the information you need in a useful, concise way.

The formula "CnHm" refers to unspecified "hydrocarbons" generally; it
is not a specific material.

Hydrocarbons are gases, liquids or solids that are made up of carbon
and hydrogen atoms only.  Here is a quote from the useful "How Stuff
Works" website that clearly explains what a hydrocarbon is:

"Hydrocarbons are molecules that contain hydrogen and carbon and come
in various lengths and structures, from straight chains to branching
chains to rings. .  .  . Hydrocarbons contain a lot of energy. Many of
the things derived from crude oil like gasoline, diesel fuel, paraffin
wax and so on take advantage of this energy.
 
"Hydrocarbons can take on many different forms. The smallest
hydrocarbon is methane (CH4), which is a gas that is a lighter than
air. Longer chains with 5 or more carbons are liquids. Very long
chains are solids like wax or tar. By chemically cross-linking
hydrocarbon chains you can get everything from synthetic rubber to
nylon to the plastic in tupperware. Hydrocarbon chains are very
versatile!"
How Stuff Works: How Oil Refining Works
http://science.howstuffworks.com/oil-refining1.htm


Based on your clarification, I am confident that the context in which
CnHm, the general formula for nonspecified hydrocarbon molecules,
interests you is its use to designate levels of impurities in
otherwise pure gases.  Here are links to two examples of that use:

At this linked site, note the table at the bottom of the page that
includes the maximum level of impurities present in Grade 6 liquid
nitrogen:
KIGC: Products: Nitrogen
http://www.kigc.com/products/nitro_specs.htm

In this case, you will see that the maximum level of CnHm (i.e.,
hydrocarbons) in that grade of liquid nitrogen is .1 ppvm (or "parts
per million by volume").


A second example from the same company shows the same maximum level of
impurity by unspecified hydrocarbons (i.e., CnHm) in the Grade 6
liquid hydrogen it produces:
KIGC: Products: Hydrogen
http://www.kigc.com/products/hydrogen_specs.htm


Search Strategy:

I found the basic information with the following Google search:

cnhm purity
://www.google.com/search?num=30&hl=en&lr=&ie=UTF-8&q=cnhm+purity

If you run that simple search yourself, you will find other very
similar examples of the term "CnHm" used in the context of describing
the purity of gases in terms of maximum presence of nonspecific
hydrocarbons.


Based on your clarification, I am confident that this is the
information you are seeking.  But if something remains unclear, please
ask for clarification before rating the answer.

markj-ga

It's any (other) hydrocarbon: any molecule with n carbons and m hydrogens.
So without n and m being specified it's not a specific one. So yes, it
must be every other CnHm gas; not "everything" else, but every (other)
n and m value.