Dear Tomasz,
For your information my background is also physics. What do you understand with pH values 10.3,
10.7 and 10.85 and propogation error for this system, etc., I will leave up to you. No further
comments.
regards
Mahendra
Tomasz Durakiewicz escribis:
> Dear Dr. Verma and Colleagues,
>
> I appreciate Dr. Verma's recent response very much. Now we have a nice
> debate and we can make Andrew happy! He was right that such discussions
> should be performed here, on this server. If we had this discussion a
> year ago, there would have been no Comment in GCA (did I use the right
> tense here?). Nancy  you wrote that chemists were so passionate. I am
> not a chemist, but a physicist. We are even worse. Our brains shrink
> when we think, leaving more space in the skull for passion and less for
> reason.
>
> OK, let us go back to the subject. Let me first summarize the discussion in
> points, from the beginning. I shall list all Dr. Verma's critical
> remarks (from his Comment and emails) and discuss them one by one. Than
> comes one suggestion and one personal statement.
>
> 1. Discussion
>
> a) Halas pH=10.3 and Verma's pH=10.85 in his Comment (GCA 64, 573574,
> 2000) and 10.7 in his recent posting. Bad chemistry argument for the
> first time.
>
> I am glad to see you finally admitt that there ARE differences between
> models, and calculation of pH does not always give the same value. Your
> simplified calculations in the Comment gave pH=10.85, whereas in your
> recent posting, calculated by activity approach for the same system, we
> find different pH=10.71. Finally, if you perform pH calculations for
> this system with the WEBPHREEQ webbased solver
> (http://www.ndsu.nodak.edu/instruct/sainieid/geochem/webphreeq/index.shtml)
> you end up with pH=10.28 for Halas's values of X1, X2 and pCO2, and
> 10.38 for values given in your recent posting. Halas in his Reply gives
> the revised value of 10.37!!!
>
> source pH
>
> Halas paper 10.30
> Halas measurement 10.30
> Verma comment 10.85
> Halas reply 10.37
> Verma file 10.71
> PHREEQ (Halas's data) 10.28
> PHREEQ (Verma's data) 10.38
>
> The most important point here, missing in your Comment, is the possible
> influence of changes in fractions of dissolved species on the calculated
> DICCO2 fractionation factor. This factor is calculated by use of eqn
> (15) from Halas's paper and the calculated fractions of HCO3 and CO32.
> These fractions in your most recent Excel file are 0.1833 and 0.8167,
> respectively. Halas's values from his Reply are 0.1828 and 0.8172,
> respectively. Room temperature fractionation factor calculated by your
> values is 4.998 and by Halas's values is 5.001. In his paper he gives
> 5.0 +/ 0.2 permil. Where is the difference? Where is the bad chemistry?
> Verma's and Halas's results are in PERFECT agreement here! And it is
> well documented by your own postings now, that problems with pH
> calculations are universal.
> As for the error propagation: eroneous 0.35 difference in pH in the
> discussed region would cause change of calculated fractionation factor
> of about 0.15 permil. This is therefore safe to report the fractionation
> factor with +/ 0.2 permil uncertainty, as is done by Halas.
>
> Conclusion: There is no bad chemistry in Halas's paper. There are
> universal problems with pH calculation, but Halas's pH calculated by 2
> different programs gives values close to obtained by his direct
> measurements. Verma's results and Halas's results for fractions X1 and
> X2 produce the same value of isotopic fractionation. We can trust this
> value.
>
> b) No HCO3 and OH terms in the ionic strength formula (8) in Halas's
> Reply (GCA, 64, 575576, 2000). Bad chemistry argument for the second
> and third time (2 postings)
>
> You need to substitute left side of eqn(1) from the Reply to full eqn(7)
> to find out that both HCO and OH terms ARE used in formula (8), although
> indirectly. This is simple addition and multiplication, and Dr. Verma is
> wrong here.
>
> Conclusion: Eqn. (8) correct, no bad chemistry.
>
> c) Water activity 0.98 impossible for this system
> You kept repeating it untill you calculated it by yourself to be
> 0.98011.
>
> Conclusion: no bad......
>
> d) Ph measurement impossible with high precission.
> To make it simple: there is a single measurement error, which is
> directly related to instrumental precision. It is additionally enlarged
> by random influences, like minute temperature changes. Let us assume
> that the maximum single pH measurement error (uncertainty) is very high, as high as
> 0.1. We know that repetitive measurements of pH are independent.
> According to the error propagation formula, we have the following
> uncertainties for the mean value of pH:
>
> number
> of measurements uncertainty of mean
> 1 0.100
> 2 0.071
> 5 0.045
> 10 0.031
> 50 0.014
>
> It is threfore enough to perform 50 measurements of pH with a poor
> precision instrument to obtain satisfactory precision of the mean value.
> There is nothing shocking in reporting the pH value with 0.01
> uncertainty.
>
> Conclusion: You are, of course, right that there are numerous problems
> associated with pH measurements. As it is with measurement of every
> other physical property. Shall we stop measuring anything because of
> associated errors? Halas gives a detailed error propagation discussion
> and the wide +/ 0.2 permil uncertainty for his fractionation factor.
> Your argument here is irrelevant.
>
> e) New argument: no water activity in eqn. (5) in the Reply
> Now, a new one. There was nothing about this in the Comment, and now it
> is the only "basis mistake". Water activity in eqn(5) was obviously set
> to 1 to simplify calculations. You must agree that dividing something of
> the order of 10^(15) by 1 or by 0.98 makes no important difference?
>
> Conclusion: Bad idea, to rise a new adhoc argument when the others
> failed.
>
> f) New argument: CO2 fractionation during cryogenic trapping in presence
> of water vapour.
> This is all described in the paper. CO2 and vapour are separated in the
> upper glass ampoule without cooling, in 25C (see Fig. 1 in GCA 61, 2691
>  2695, 1997) by turning the stopcock. Than both CO2 and H2O are trapped
> cryogenically in a small ampoule. Than CO2 is released for measurement
> and water remains as a solid in the ampoule. This is all done fast. How
> could there be any significant dissolution of CO2 in water in this
> experiment? There is supposed to be NO LIQUID WATER there, only water
> vapour and frozen solid. Presence of trace amounts of liquid water that
> could form on the walls due to temperature instabilities in high
> temperature range, could possibly explain variation of results obtained
> for high temperatures (together with the stopcocks problems reported in
> the paper). But we have to understand one thing  this is not any major
> drawback, but quite contrary, this was done with great care and reported
> honestly.
>
> Conclusion: same as in point e)
>
> g) New argument: there should be no "fundamental experiment (like in
> discussion) where there is need of
> correcting isotopic measurements with chemical analysis"
>
> Wrong! All the isotope exchange experiments are like this. What was
> measured in this experiment? Weight of reagent, volume of water, pH,
> temperature, isotopic compositions of reagent, DIC and CO2. Shall we
> stop doing such experiments because they are difficult? This is the only
> way to do this. As Dr. Jedrysek (my friend isotope geologist from
> Wroclaw) used to say to his students: in this lab you shall find pain,
> work, sweat, tears and kicked ass. This is science, I presume.
>
> 2. Suggestion
> Having boxed Halas in public for a while, you say in your recent
> posting: "my comments are just some suggestions,
> which may be considered during their work". This is true, but the
> meaning of your Comment and postings was quite different. I suggest you,
> Dr. Verma, to send a letter to The Editor, GCA, stating that you were
> wrong in raising the "bad chemistry problem" in the Halas's paper. Or at
> least admit this here.
>
> 3. Personal
> Nothing personal! I learned a lot last days and I am grateful for this
> possibility. It looks like I will stay in New Mexico for a while. Being
> so close to each other, we will probably have a possibility to meet and
> have a couple of beers. Or better some Polish Bison Vodka, really cold,
> not shaken. No hangover guaranteed.
>
> With best regards,
>
> Tomasz Durakiewicz
>
> ***************
>
> Mahendra Pal Verma wrote:
>
> > Dear Colleagues,
> >
> > I don t know whether I should continue on this matter or not. It looks that there are
> > some who are interest in knowing it. In my opinion, too, the Isogeochem Server is a
> > good opportunity to discuss our viewpoints and improve our understanding with the
> > comments of others. Let me write first that I am a regular reader of GCA and it
> > publishes excellent material. Of course, it is well established. My comments were only
> > that the reviewers should put more attention when a mistake had been pointed out.
> > People at least I use the information published there as granted.
> >
> > I worked out the problem using the activity approach. The data are given in the
> > attached file. I use Error and Trail method to solve a nonlinear equation. I do it
> > in excel without writing any programming code. I don t think that anyone is
> > interested in that. The basis mistake in the reply by Halas et al. (GCA, 64, 575576,
> > 2000) was that their equation 5 should be K3=a(H)a(OH)/a(H2O). The values are given
> > for their system (10 g Na2CO3+CO2 from 1g of Na2CO3). Again, there could be small
> > differences if you use different constants. I tried to use the same constants as were
> > given by Halas et al. I did the calculation without recheck. So,
> > there could be some mistakes. I think it could be better if Halas et al. change
> > equation 5 and recalculate the parameters.
> >
> > Recently, we have started a project to study rainwater acidity around geothermal
> > systems. We observed that it was really difficult to measure pH of pure water like
> > rainwater with a pHmeter (rainwater characterization is based on pH around the world).
> > Similarly there are problems in measuring pH of highly
> > acidic or alkaline (more in case of alkaline) waters. (we are working to understand this).
> > Additionally, the IAEA has
> > conducted three interlab calibrations (Giggenbach, IAEATECDOC641, Vienna,
> > p.439456, 1989 and two are very recent). If you look these reports, you will find
> > that there is some improvement in the analysis after 10 years; but the quality of analysis
> > of
> > especially SiO2, HCO3 and CO3 is far bellow the expectations. That is different topic
> > how to improve it. But the results indicate that in my viewpoint one should not
> > design a fundamental experiment (like in discussion) where there is need of
> > correcting isotopic measurements with chemical analysis. As I tried to explain it in
> > my comments. The calculated ratio of HCO3:CO3 is 18:82. So there is need of correcting the
> > HCO3 contribution. One can calculate the propogation of error in their isotopic data due to
> > the error in the chemical analysis.
> >
> > Secondly, the partial pressure of CO2 in vapor phase is very low (much less than
> > 10^4 bars). If you are extracting 10 micromoles, you can calculate how much volume
> > should be of the experimental vessel and how the vapor phase CO2 can be extracted
> > only without changing its isotopic composition. The amount of water vapor will be
> > much higher than that of CO2. Check the steam tables. When you condense this vapor
> > some part of CO2 will get dissolved in the water. So there will be some fractionation
> > in this process, too. So, there are many points one has to consider for this work. I
> > do agree that some thing is better than nothing. This way the calculated values (with
> > spectroscopic data) could be more accurate than the experimentally measured. The
> > measurement of isotopic
> > fractionation for CO2(g) and carbonate is a challenging subject. Definitely, it is
> > hard job to work on this type of problems. So, we should do encourage the people who are
> > working such types of problems. My comments are just some suggestions,
> > which may be considered during their work.
> >
> > Best regards
> >
> > Mahendra
> >
> > 
> > Name: calFnl.xls
> > calFnl.xls Type: Download File (application/xmsexcel)
> > Encoding: base64
