Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

19th century matches: Chlorates without electrolysis?

  1. Dec 1, 2014 #1
    First, I completely understand that electrolysis to produce chlorates is simple, practical, and inexpensive. I understand that electrolysis to produce chlorates was being used in the late 19th century. I'm wondering, given the (somewhat) limited distribution of electrical power at the time and the ubiquity of chlorates for the production of friction matches, if there was a practical non-electrolysis method of producing chlorates.

    Wikipedia talks about combining "hot metal hydroxides" (presumably molten) with chlorine gas producing the chlorate. A balanced equation can be written:
    6 KOH + 3 Cl2 = 3 H2O + 5 KCl + KClO3
    But that doesn't mean it reacts that way. Indeed, the melting point of KOH is above the dissociation point of KClO3. :)

    It appears that you could, theoretically, work your way up from hypochlorite, starting with chlorine gas dissolved in water, with lots of hydrogen chloride produced and discarded:
    Cl2 + H2O 15px-Equilibrium.svg.png HClO + HCl
    3HClO + heat → HClO3 + 2 HCl
    KOH + HClO3 → KClO3 + H2O
    But again, just because you can write the equations doesn't mean the reaction will happen or that it's practical.

    Anyway, I'm curious about how "all that perchlorate" was made back-in-the-day. If anyone has a pointer to a practical historical method, I'm all ears. My Google searches all seem to turn up the electrolysis route, to the exclusion of everything else.
    Last edited: Dec 1, 2014
  2. jcsd
  3. Dec 1, 2014 #2


    User Avatar
    Science Advisor
    Homework Helper
    Gold Member

    Calcium hypochlorite was manufactured commercially as a bleaching powder for most of the 19th century, and it's almost impossible to prevent disproportionation of hypochlorite to chlorate and chlorine; so if you're in the bleach business in those days, you're almost stuck with production of chlorate whether you want to be in the business or not. The chlorine can be run back through the lime vats to produce more hypochlorite, so it's not a loss, and there is/was a market for the chlorate.
  4. Dec 1, 2014 #3
    Thank you, bystander!

    Reading up on bleaching powder, I see that excess chlorine beyond that required to neutralize the calcium hydroxide pushes things to a chloride/chlorate mixture, and that the two are difficult to separate. This process description addresses the problem of separating the chloride and the chlorate by the addition of potassium chloride, producing calcium chloride and potassium chlorate, which are then separated by fractional crystallization. This would certainly have been manageable and scalable historically.

    Thanks again,
  5. Dec 2, 2014 #4


    User Avatar
    Science Advisor

    Nurdrage, my favorite internet chemist, has this video on how to produce chlorate from bleach:

    Eau de Javelle was produced since 1792 in Javel, now part of Paris, so it was available during the entire 19th century.
    Last edited: Dec 2, 2014
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook