[Jewelry making - Article 01357] - Re: [Orchid] Different mixtures of Propane

[Brian Adam]

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    I've discovered a few interesting things over the years. Here in New
    Zealand the 'propane' sold for use in cars (LPG) is a mix of propane
    and butane, the percentages vary by brand, but roughly 60/40. 

    I believe the butane in the mixture tends to stratify (down) if the
    tank is left standing. Naturally in an automobile the tank gets a
    good old shake about. However for jewellery use the stratification
    could be a problem so that towards the end of the bottle you may be
    burning butane, and butane's also reputed to be harder to ignight as
    a torch gas in the colder months. 

    Another problem associated with the mixture emerged. Over the years
    we've noticed that our torch heat-colouring of titanium becoming more
    and more erratic, with spots appearing where we didn't want them.
    After theknee-jerk reaction that is was Ractive Metal's metal, we
    investigated the gas in our bottles. Turns out that the butane % in
    our local gas was increasing! I found a source in Auckland of 96%
    propane LPG, and use that bottle for heat-colouring. 

          Why are Butane and Propane used in combination? While butane
          and propane are different chemical compounds, their properties
          are similar enough to be useful in mixtures. Butane and Propane
          are both saturated hydrocarbons. They do not react with other.
          Butane is less volatile and boils at 0.6 deg C. Propane is more
          volatile and boils at - 42 deg C. Both products are liquids at
          atmospheric pressure when cooled to temperatures lower than
          their boiling points. Vaporization is rapid at temperatures
          above the boiling points. The calorific (heat) values of both
          are almost equal. Both are thus mixed together to attain the
          vapor pressure that is required by the end user and depending on
          the ambient conditions. If the ambient temperature is very low
          propane is preferred to achieve higher vapor pressure at the
          given temperature. 
          http://www.e-lpg.com/lp_gas.asp. 

Brian

B r i a n   A d a m   
e y e g l a s s e s   j e w e l l e r y
Auckland NEW ZEALAND
www.adam.co.nz

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