To mix by weight you must consider the specific gravity of each (0.77g/cc
for IPA). I would mix by volume with both materials being the same
temperature (room).

On Thu, Jun 29, 2017 at 11:30 PM, Brian Ellis <[log in to unmask]> wrote:

> Just a little question re mixtures of IPA and water. Let's say you want a
> 75% mixture. Do you...
> a) weigh 75 g of IPA and 25 g of H2O? If so, at what temperature for each
> component?
> b) measure 75 ml of IPA and add 25 ml of water? If so, at what temperature
> for each component?
> c) measure 75 ml of IPA and add water to make up to 100 ml? If so, at what
> temperature for each component?
> d) measure 25 ml of water and add IPA to make up to 100 ml? If so, at what
> temperature for each component?
>
> Assuming the temperature is the same for the two components (big if, in
> many cases!), each of the four solutions above will be very different from
> each other (of course, also applies to 50% solutions). The problem is
> because mixtures of the two liquids do not form an ideal solution. The
> loose structure of the water molecules leaves space for the tight structure
> of the IPA molecules to fit in (simplified explanation - look up wiki Ideal
> Solution.)
>
> If you do a scientific test with each of the four mixtures, you will find
> that the measured conductivity after injecting a known quantity of a test
> solution will vary by up to 15%.
>
> Just a thought...
>
> Brian Ellis
>
> On 29/06/2017 00:25, Joe Russeau wrote:
>
>> Hello Rich,
>>
>> To the best of my knowledge, I am not aware of a statement to that
>> affect in any IPC document that I have read.  If there is such a
>> statement, then I would say it is an erroneous one and needs to be
>> addressed.  There is HPLC grade IPA, which usually refers to 99.5% or
>> higher purity.  There is also Electronic-grade IPA, which has the same
>> purity as HPLC.  Then there is Technical grade IPA, which I believe is
>> usually classified as anything above 90% purity.  IPA is a chemical and
>> its percentage of purity doesn't define whether or not it is still an
>> "IPA",  it's chemical formula defines that. The % only defines how much
>> junk is left behind in the solvent.  Now, there are IPC methods that
>> deal with the percentage of the starting IPA, such as the ROSE and Ion
>> Chromatography methods, and the reason is to minimize adding error into
>> the measurement system that could skew the results for an actual
>> sample.  If there is a statement as you indicate below, can you ask
>> whoever told you that which IPC document states such a thing?  If not, I
>> wonder if someone might have misread that part of the document
>>
>> Best Regards,
>>
>> Joe Russeau
>>
>>
>>
>> -----Original Message----- From: Richard Kraszewski
>> Sent: Wednesday, June 28, 2017 4:48 PM
>> To: [log in to unmask]
>> Subject: [TN] IPC definition of alcohol
>>
>> I have been lead to believe that there is a definition within IPC
>> documentation  for  IPA (isopropyl alcohol).
>> That it defines that anything greater than  "XX%"  IPA shall be
>> considered IPA.
>>
>> Any thoughts?
>>
>>
>> Rich  Kraszewski
>> Senior Staff Process Engineer
>> Plexus Engineering Solutions
>> Ship To - 2444 Schultz Dr. Neenah, WI 54957-2444
>> Mail To - P.O. Box 2444 Neenah, WI 54957-2444
>> Phone: (920) 969-6075
>> www.plexus.com/(NASDAQ PLXS)
>> [log in to unmask]
>>
>>
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Brian Stumm
ETS, Inc.
+1-509-276-2015