While we now understand the crystallography of diamonds, and most, if not all, of their chemical properties, this was not always true. The exact nature of diamonds was a mystery to scientists for many years; many people struggled with the “indestructible” nature of diamonds. It was widely known by the 17th century that they could be cut and polished; this seemed at odds with the idea of them being indestructible. Some scientists began to conduct experiments to investigate this.
In the 1690s, Grand Duke Cosmo persuaded the Academy of Cimento in Florence to conduct one such experiment. A diamond was fixed into the focus point of a large magnifying glass, and exposed to intense sunlight. To everyone’s astonishment, the diamond cracked, and then disappeared, without leaving the slightest trace behind. It seemed like magic; some suggested sleight of hand, trickery or even theft. What was certain was that the diamond was not there any more.
This remained a little mystery for many years, and it wasn’t until the late 18th century that an explanation was found. Two experiments were conducted in the 1770s which shed some light on the case. Firstly, a Monsieur Le Blanc, a Parisian jeweller, was persuaded to put a parcel of diamonds into a crucible. This did not trouble him, as he often heated them during the course of his business. However, after three hours of heating in the crucible, the diamonds were gone!
A solution was discovered by French scientist Antoine Lavoisier, a nobleman prominent in the histories of chemistry and biology. He named both oxygen and hydrogen and predicted silicon. In the next experiment, the diamonds were packed in powdered charcoal, and placed in a bowl before being heated. After three hours of heating, the diamonds were still there, as good as before. He wondered why had one experiment caused the diamonds to disappear, and in another they stayed the same?
Lavoisier concluded that it was the presence of oxygen which made the difference; a free supply of oxygen caused the diamond to convert completely into carbon dioxide! A further test confirmed this; the diamond was burned in a sealed jar. Lavoisier noted the overall weight of the jar was unchanged and that when it burned, the diamond had combined with oxygen to form carbon dioxide.
We do not, of course, recommend that anyone try this at home!!!!