I'm not Mr. Acid-Expert but 'pure' acid is one unadulterated, or diluted, with water.(And, to be honest, I am not sure that all acids are miscible with water but I'd say they are) Glacial basically means that: without water. Formic acid is what ants lay down as a trail and they consist a bit of that. Acetic acid (in photography we use a diluted form but can purchase it as 'glacial') is similar to that in vinegar which is generally a 5% solution Hydrochloric (often times, and in hardware stores called 'muriatic') acid is what we have in our stomachs (gastric acid) Sulphuric (sometimes in US, 'sulfuric') is used in batteries for autos in a dilute form Nitric acid is very strong and able to reduce metals Then a really strong combo of nitric and hydrochloric (1:3) is called aqua regia (king water) and that can reduce gold and platinum but even though it is a mixture of acids I don't think it is technically an acid.
Jack F On Sep 6, 2008, at 6:59 PM, Christina Z. Anderson wrote: What might be a pure acid? Glacial? Or sulfuric or phosphoric? Or hydrochloric? I have all four here... So you are saying that sodium ascorbate (isn't that what Vit C is) is present to a significant amount in lemons to make more of a difference than the actual acid in lemon juice? So the test would be lemon juice against other acids? Interesting... This is what is so useful about this list... Chris __________________ ----- Original Message ----- Sent: Saturday, September 06, 2008 7:05 PM Subject: RE: gum preservatves
Chris,
Very informative experiment. I do not think that effect is due to acidity. I would rather put out a hypothesis that the effect is due to the vitamin C (ascorbic acid) present in lemon juice. Vitamin C is a strong reducing agent that would react quickly with dichromate reducing it to Cr (III) and making gum insoluble. Kind of like a dark reaction in gum, no light needed. It appears as a stain, but it really is not. It is really a chemical fog.
ANyways to test acidity one would use solutions of pure acids.
Marek
> Date: Sat, 6 Sep 2008 15:49:18 -0600
> From: zphoto@montana.net
> Subject: Re: gum preservatves
> To: alt-photo-process-l@usask.ca
>
> Here it is:
>
> http://christinazanderson.com/Text_page.cfm?pID=2076
>
> Scroll down to the very bottom past the color charts.
>
> I'm not saying it proves anything, but acidity may account for some problems
> that people say are issues with gum, and it is only really meaningful in
> relation to the water control strips done at the same time with the same
> amounts of dilution. Otherwise a lot more tests would have to be done to be
> conclusive. If, as Ryuji and Demachy said, there is a reduction to chromic
> acid with the addition of lemon juice, which I don't know because I am not a
> chemist, I don't know if that is speedier or less speedy than dichromate.
> Chris
> __________________
>
> Christin a Z. Anderson
> http://christinaZanderson.com/
> __________________
> ----- Original Message -----
> From: "Loris Medici" <mail@loris.medici.name>
> To: <alt-photo-process-l@usask.ca>
> Sent: Saturday, September 06, 2008 3:13 PM
> Subject: Re: gum preservatves
>
>
> Thank you!
>
> Now that you say that, I remember the section about it in the "Learn" part
> of your former website. (Adding lemon juice and staining... I'm not making
> it up right?)
>
> Judy's note on sizes was interesting and real food for thought, BTW.
>
> Ryuji's notes also were interesting -> I mean the probability of citric
> acid (or any other organic acids) interacting with dichromate in an
> unwanted manner. That powered my original position which was increasing
> the acidity by not adding alien compounds... (Still don't know if that can
> work or not -& gt; I may do some tests in the future if the exposure times
> become unbearable to me and/or I can't do nice casein prints...)
>
> Regards,
> Loris.
>
>
> 5 Eylül 2008, Cuma, 1:12 am tarihinde, zphoto@montana.net yazmış:
> >
> > ...
> >
> > Have at it, Loris. I found that the more lemon juice drops
> > I added to the mix (with drops of water added to the control
> > group in the same proportion) that I got lots of staining of
> > the highlights and lower contrast, but with paper negs this
> > might be helpful to you--I mean, the lower contrast part.
> > Step wedge steps were not too differentiated.
> > Chris
> >
> > ----- Original Message Follows -----
> > From: Loris Medici <mail@loris.medici.name>
> > To: alt-photo-process-l@usask.ca
> > Subject: Re: gum preservatves
> > Date: Thu, 04 Sep 2008 21:37:54 +0300 (EEST)
> >
> >>David & Chris, that also arrived to my mind just after had
> >>sent my last message... Even if I refrain to introduce
> >>another alien compound into consideration - as a first
> >>impression -, it sounds interesting / promising. You can
> >>bet I will try this (with citric acid)as soon as possible!
> >>Of course there's also the staining issue... I'll see.
> >>Thanks!
> >>
> >>Chris, do you know how much lemon juice was Demachy adding
> >>to his gum?
> >>
> >>Regards,
> >>Loris.
>
>
>
>
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