[Jewelry making - Article 00343] - Re: [Orchid] Sparex No 2 101

[leonid surpin]

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>     If there's any such thing as pulmonary arrest as a reaction to
>     sulfuric acid, it's news to me. 

    If your comment means that breathing in acid vapors do not have
    consequences, than you should take your own advice and check the
    facts. Also consider that having any chemical liquid open will result
    in evaporation and vapors will carry minute particles of the liquid (
    acid in our case ) with them, so if you are in the room with the open
    container containing the hot liquid, you are breathing it in. 

    The hotter the liquid, the more pronounced the effect. Pulmonary
    arrest implies immediate reaction to a contact. That is not what I
    wrote. 

    Prolonged contact with acid leads to neurological damage which can
    lead to severe damage to lungs and pulmonary arrest as a consequence.
    Beside if smoking is dangerous, what do you think pickle vapors doing
    to your lungs? 

    Dilute sulfuric acid does not dissolve copper, period. Hot
    concentrated acid does, but that's another story. If it did, you
    would shortly not have a vessel, now would you? 

    What needs to be understood here is the action of boiling a
    jewellery in a copper vessel containing dilute sulphuric acid is not
    the same as conducting reaction between copper and dilute sulphuric
    acid. 

    I will help you to understand this process. 

    First what must be realized is that text book reactions assume pure
    components which do not exist in real world. Second is the
    concentration of the solution is changes as boiling progresses. 

    With this in mind let's examine what happens in the pot. The purpose
    of pickling is not only to remove melted flux but also to remove
    oxides. Working with gold alloys creates copper oxide since most of
    practical gold alloys contain copper. Copper oxide react with dilute
    sulphuric acid readily. 

    Cu2O + H2SO4 = Cu + CuSO4 + H2O 

    In words the result is copper, copper sulphate, and water. So the
    process like this. We put jewellery in a copper pot, add dilute acid
    and boil it under the hood. Flux is dissolved together with copper
    oxides, pure copper is deposited on the bottom of the pot and copper
    sulphate stays in solution. 

    Remaining acid stays a pot since since, like you stated, it does not
    reacts with copper, but I would add to this practically, since there
    is no such things as total inertness. 

    Immediately after boiling the concentration of the acid increases
    due to water evaporation and some consumption of deposited copper
    takes place, but since sulphuric acid is hydroscopic, the
    concentration will fall in time. Eventually solution turns blue and
    needs to be replaced. 

    but the danger of mixing and storing acid is far outweighed by that,
    which is why the industry lives on Sparex. 

    Here is the link to sodium bisulfite MSDS 

    http://physchem.ox.ac.uk/MSDS/SO/sodium_bisulfite.html 

    Anybody who thinks that it is safer than sulphuric acid should read
    it. Pickle based on sulphuric acid you keep cold and bring it to boil
    only when needed, Sparex must be kept hot in a busy shop. It works
    cold but takes too long. So even if we assume it is 100% effective,
    which is not, the exposure to hot vapors throughout the day is far
    more dangerous than having cold container of dilute sulphuric acid. 
As
    far as handling the acid, it is not that complicated. 

>     I am sorry if this is blunt, but please check facts before
>     posting. Misinformation about chemistry is dangerous and quite
>     easily researched before hand. There is much chemical lore in our
>     trade, but it's quite simple to check the facts, if one is inclined
>     to. 

    I like blunt. I am not much into mincing the words myself, so it is
    always good to remember that what appears as misinformation could be
    our haste in judging the information and failure to understand the
    process for what it is. 

    Frankly, when I started in this business, one could not even find a
    bench without a small copper pot hanging on the side of it, used for
    pickling. Everybody used his own. My first exercise in working with
    metal was making a scoop for filing and the second was making a 
pickle
    pot out of copper. So I am really surprised that you are not aware of
    this procedure. 

Leonid Surpin.
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