[alt-photo] Solution dilution conundrum

[Greg Schmitz]

I have followed both of the recent threads, "Zia standard solutions" and 
"dilution of pt/pd" with some interest - for a variety of reasons.

I've been working with photographic chemistry for 40+ years now and have 
used both systems.  Early on, while still in high school and after 
taking my first chemistry class, I started using molar solutions 
(thought I was being smart - at least all of those old timers).  As I 
recall, no Google searches on this one (it's burned into my brain)  a 
mole is 6.02 x 10 ^ 23 [approximately]) and expresses the number of 
atoms in a solution (very acurate - no?)

You'll forgive me if I don't recall all the details, I abandoned using 
molar solutions in my darkroom for a variety of reasons.  First off, 
since I was trying to pay the rent, I had to use "chemistry" that was 
made by other people - and thus I couldn't, with confidence calculate 
molarity with any degree of confidence of proprietary formulations.  
Second, most texts on photography, old and new - at least those written 
with regard to day to day chores and not research, use percentage 
solutions not molar solutions.  Third, because I was trying to pay the 
rent, I didn't have time to do the required conversions to get from 
popular articles that used percentage solutions to molar (no computers 
or digital calculators back then - only slide rules and paper).  All in 
all setting molarity aside was just a practical matter.

I wouldn't discount the value of using molar solutions esp. for "post 
factory processes" (thank you Judy) that I was trying to modify or 
recreate.   But if I were to publish anything about what I found out 
about how all those tiny particles co-mingled with each other for the 
general photographic community I would use percentage solutions, because 
that is the language that most folks are used to.

Hope this makes sense, have a nice day!

--greg