The following pagargraph is from the Wikipedia page of calomel:

Mercurous chloride is employed extensively in electrochemistry, taking advantage of the ease of its oxidation and reduction reactions. [...] Over the past 50 years, it has been superseded by the silver/silver chloride (Ag/AgCl) electrode. Although the mercury electrodes have been widely abandoned due to the dangerous nature of mercury, many chemists believe they are still more accurate and are not dangerous as long as they are handled properly.

Yes, the calomel electrode is a breakthrough in electrochemical industry due to its ease of its oxidation and reduction reactions. But, the nature of mercury is such that every chemist fears it. There has been cases of mercury poisoning and deaths related to it. Despite its toxicity, electrochemist prefer the SCE over the silver/silver cloride electrode. Why?

Due to its toxicity, the SCE has almost been replaced by the silver/silver chloride electrode. But still, the SCE is used as a reference electrode. Why? Why is the silver/silver chloride electrode not as good as the SCE?

Also, what are the safety measures/protocols undertaken by electrochemists while performing experiments using the calomel electrode?

  • 1
    $\begingroup$ It was replaced by Ag not the other way round. $\endgroup$
    – Mithoron
    Oct 31 '16 at 18:42
  • 2
    $\begingroup$ I’m not scared of mercury. None of my colleagues are, either. $\endgroup$
    – Jan
    Nov 1 '16 at 23:51

[…] Why and how chemist are still able to perform experiments using Calomel electrodes despite its toxicity? […]

I mostly used non-aqueous silver electrodes as a reference for my measurements in acetonitrile.

But I wouldn't be afraid to use a saturated calomel electrode (SCE) when necessary. We have recently discussed the toxicity of mercury metal and I think it is largely overrated.

As far as $\ce{Hg2Cl2}$ (calomel), the other mercury component in the SCE is concerned, have a look as the wikipedia article that you have cited yourself. The solubility is extremely low ($\mathrm{2.3\ mg\cdot l^{-1}}$) and the ${\mathrm{LD_{50}}}$ is $\mathrm{210\ mg\cdot kg^{-1}}$ (rat, oral uptake). This isn't overly dramatic either, when compared to the infamous potassium cyanide (${\mathrm{LD_{50}}}$ $\mathrm{5\ mg\cdot kg^{-1}}$, rat, oral uptake).

Actually, calomel had medical uses :)

In an article on Venereal disease prevention, the author writes:

[…] the absence of therapeutic modalities spurred the United States Armed Services to utilize Credé's solution for urethral irrigation and locally applied calomel ointment for prophylactic purposes in World War I […]

As far as the toxicity is concerned, both mercury metal and mercury(I)chloride are by no means comparable with dimethylmercury.


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