History of Science in Bite-Sized Chunks by Nicola Chalton

Author:Nicola Chalton [Chalton, Nicola & MacArdle, Meredith]
Language: eng
Format: epub
Publisher: Michael O'Mara

The Law of Substitution: Jean-Baptiste Dumas

In the early nineteenth century the accepted theory of molecular structure was that all chemical compounds were either positive or negative, and chemical combinations resulted from the attraction of the opposing parts. This ‘dualistic’ theory was particularly championed by Jöns Jacob Berzelius.

But the French teacher and politician Jean-Baptiste Dumas (1800–84) found that burning candles bleached with chlorine produced fumes of hydrogen chloride, and concluded that ‘during the bleaching, the hydrogen in the hydrocarbon oil of turpentine became replaced by chlorine’. He had shown that in certain circumstances it was possible to substitute the hydrogen atoms (that were electropositive) with chlorine or oxygen atoms (electronegative) without there being any dramatic structural change.

Berzelius and others, including Justus von Liebig (see here), disputed these findings so strongly that Dumas retreated from his position. But in the long-run this theory did supersede that of Berzelius.

Less contentious was his work identifying the components of compounds such as urethane and methanol by distilling wood. He also improved methods of measuring vapour densities by finding the mass, temperature, volume and pressure of a substance in its vapour phase. This led directly to the more accurate atomic weights of thirty elements, half the total number known at the time.

Dumas was a pioneer in the study of organic chemistry. Like Liebig, he was also one of the first teachers to insist on scientific laboratories and rigid experimentation. But, despite all his achievements, he was not above using his eminent position in the Academy of Sciences to hinder the careers of younger chemists whom he feared threatened his reputation.

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