Wednesday, August 8, 2012

Synthesis v. Analysis

Around the time that America began civil warfare, reports of a new chemical element came from the relative tranquility of Germany. Robert Bunsen and Gustav Kirchhoff reported in 1861:
Supported by unambiguous results of the spectral-analytical method, we believe we can state right now that there is a fourth metal in the alkali group besides potassium, sodium, and lithium, and it has a simple characteristic spectrum like lithium; a metal that shows only two lines in our apparatus: a faint blue one, almost coinciding with strontium, and another blue one a little further to the violet end of the spectrum and as strong and as clearly defined as the lithium line.
They had discovered cesium which they named after the Latin word meaning "sky blue." 

There had been a 15 year lull in finding new chemical elements between about 1845 and 1860. One reason for this was that many of the "easy" elements had already been exhumed in measurable enough quantities. Here is a timeline of element discovery: link 

The mid-19th century saw advances in both chemical synthesis and chemical analysis. Chemical synthesis, obviously, involves putting things together; analysis means tearing substances down to find out what's there (the same dichotomy exists in writing).

Decades before Bunsen and Kirchoff, Humphry Davy proved the existence of new chemical elements by making them: he electrolyzed sodium and potassium salts, reducing Na+ and K+ cations to their neutral metals.*  Now Bunsen and Kirchhoff had shown the same level of proof through analysis without synthesizing the new element. This paradigm shift was profound and rapidly accelerated the discovery of newer elements (see the timeline).  The next few newly-discovered elements were all named for their unique colors in flame spectra.

Around the same time as Bunsen and Kirchoff, the nascent science (really art) of organic chemistry still lagged because there was no convincing method of analysis which could prove a new organic compound.  There was only combustion analysis--invented in the 1820s by Joseph Louis Gay-Lussac and Justus von Liebig--which involved burning a sample to determine its carbon, hydrogen, and nitrogen ratios.  And so, for the time being, the proof of a new organic compound's structure found in nature lay in making it synthetically. Thus began a long and rich tradition of synthetic organic chemistry. It took until the end of the Second World War for analytical methods to catch up.
*The verb "to reduce," in the chemical sense, derives from Latin using the notions of re + ducere = to lead back to (the element).


  1. There's always a building up and a tearing down, accept when there's just a race to out degrade each other.

  2. Thanks. I suppose we could draw an analogy from this.

  3. Thanks. I suppose we could draw an analogy from this.

    Flame wars?

  4. Modern day discovery of new synthetic elements requires both making them and analyzing them, so the paradigm shifted again in the 1930's and 40's.