The Standing Invitation

Chemistry in 1911 Was Just Adorable

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What was the cutting edge of chemical research a century ago? Fortunately the Journal of the American Chemical Society stores PDFs of papers published as early as 1879. What was contained in the issue from one hundred years ago this month?

The paper that stands out for me is by Otto Folin and Fred F Flanders, and is called simply The Determination of Benzoic Acid. I find it adorable beyond words.

Benzoic acid is a simple compound that occurs naturally in many plant and animal species. Extracting it from an aqueous solution is now a common experiment for first-year undergraduates: add a little HCl and a lot of chloroform, and the benzoic acid will migrate to the chloroform layer; then separate the chloroform layer, evaporate off the chloroform and you’ll be left with pure compound. When all you’re doing is getting benzoic acid out of water, it’s almost impossible to get it wrong (although somehow, when I was an undergraduate, I managed…); but if there are a whole bunch of other, similar compounds in the water too, then obtaining the benzoic acid pure is much more difficult.

So Folin and Flanders dedicated themselves to developing techniques for obtaining pure benzoic acid from cranberries (I love this so much). They were able to find the amount of benzoic acid in the chloroform layer directly by measuring the acidity of the solution – an improvement over removing the chloroform by evaporation since, in the days before rotary evaporators, this would have involved just leaving the flask open on a bench for a couple of days.

But cranberries were too easy, they say. They demanded a harder challenge. And so they turned their attention to catchup.

Reading this I had no idea what ‘catchup’ was. It turns out to be an early alternative spelling of ‘ketchup’ (they also spell ‘definite’ and ‘volatile’ without the final e). Catchup is essentially tomatoes preserved by acid: the acid prevents bacterial growth.

Extracting benzoic acid from catchup was made complicated by the presence of these various acids. They tended to end up in the chloroform layer alongside the benzoic acid and needed to be taken care of. Folin and Flanders eventually removed these impurities with carefully pH-controlled aqueous washes; by recording the pH at which each acid came out, they were able to identify many of the acids.

Using this technique they were able to find the amount of benzoic acid in two of the sauces – Snider’s catchup and Heinz’s catchup. Their technique wasn’t perfect – the benzoic acid never came off entirely clean (the impurity was probably the chemically similar cinnamic acid), and wasn’t accurate for levels higher than 0.1%, but as a simple test that only takes 90 minutes and lets you recover the chloroform afterwards, they seem rightly pleased with it.

Rather cute, really, isn’t it?

 

REFERENCES

Original paper: http://pubs.acs.org/doi/abs/10.1021/ja02223a010

See the Wikipedia pages for benzoic acid, cinnamic acid, and a surprisingly detailed discussion of the etymology of the word ketchup.

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Written by The S I

October 27, 2011 at 11:59 pm

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