It seems like the typical laboratory methods for determining the carbon content of steel are to cuppellate it in a stream of oxygen and then measure the volume of the evolved $\ce{CO}$ and $\ce{CO2}$, which involves many high-temperature complexities.

Why can't the carbon content of steel be measured by dissolving it in acid and reacting out the carbon at low temperature?

  • $\begingroup$ I am interested to know what happens the the carbon when steel when it is reacted with acid. Would the reaction be different in nitric acid vs hydrochloric? $\endgroup$ Commented Jun 22, 2015 at 2:54
  • $\begingroup$ I don't know much about metallurgy. I think reaction of steel with acid leads to corrosion. So does corrosion play any role here? $\endgroup$
    – Freddy
    Commented Jun 22, 2015 at 6:49

1 Answer 1


I think cuppellate is a foreign word meaning "burn" essentially.

The basic technique would be to have the iron sample in a small ceramic boat which is put into a hot stream of $\ce{O2}$ so the iron and carbon both oxidize. The iron oxide stays in the boat, and the $\ce{CO2}$ is sweep away and trapped/reacted somehow. We talking small samples 10 grams perhaps.

If you try to dissolve the steel in an acid solution then the $\ce{CO2}$ gas is formed in solution. It is really hard to get a small amount of $\ce{CO2}$ out of solution given that you are starting with a small amount to begin with. Also if you try to scale up such a reaction it gets to be a problem. A $2~\mathrm{cm^3}$ block of iron takes a long time to dissolve in acid.

So choosing the analytical method depends on a lot of factors. Time per sample, sensitivity, and overall cost being the main ones.

  • $\begingroup$ May I introduce you to the \ce{...} notation? Use that in MathJax to get upright chemical expressions. E.g. $\ce{C + O2 -> CO2}$ gives $\ce{C + O2 -> CO2}$. Learn more on meta $\endgroup$
    – Jan
    Commented Oct 31, 2015 at 0:08

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