Stories About Chemistry
38. Little Stories from Archeology
When did man first begin to use iron? The answer seems self-evident: when he learned to smelt iron from its ore.
Historians have even established the approximate date of this great event, the date of the beginning of the “Iron Age” on Earth. But actually the Iron Age started before the primeval metallurgists produced the first kilogram of iron in the primitive blast furnace. Such was the conclusion drawn by the chemists armed with mighty methods of analysis.
The first pieces of iron used by our antecedents literally fell from the sky. What we call iron meteorites always contain nickel and cobalt besides iron. Now when analysing some of the most ancient iron tools chemists found them to contain iron’s neighbours in the Mendeleyev Table, namely, cobalt and nickel. These metals are by no means always present in the iron ores on Earth.
Is this conclusion quite unquestionable? Not a hundred per cent, anyway. The study of antiquity is a very difficult matter. But here one is very likely to come up against the unexpected.
Archeologists once sprang the following surprise on the historians of chemistry. In 1912, while carrying on excavations among ancient Roman ruins near Naples, Professor Günther of Oxford University found some glass mosaics of surprising beauty. The colour of the glass did not seem to have faded in two thousand years.
To establish the composition of the colouring matter used by the ancient Romans Günther sent two samples of pale green glass to England where they fell into the hands of the chemist Maclay. The analysis showed nothing unexpected, not to mention some impurity amounting to about one and a half per cent.
But what this impurity was, Maclay could not say.
Chance saved the situation. It occurred to someone to see whether the impurity was radioactive. This was very fortunate, for the impurity actually displayed radioactivity. But what element could have caused it?
The chemists reported the unknown impurity to be uranium oxide. Was this a discovery? Hardly. Uranium salts had rather long since been used for colouring glass. It was one of the first practical uses of uranium. But in the Roman glasses uranium was evidently a chance admixture.
That put an end to the story for the time being. But some decades later this forgotten fact came to the knowledge of the American archeologist and chemist Kelly.
After extensive investigations, repeated analyses and comparison of various data, Kelly came to the conclusion that the presence of uranium in the ancient Roman glasses was the rule rather than the exception. The Romans knew about uranium minerals and used them for practical purposes, particularly, for colouring glass.
Perhaps this is where uranium’s biography starts?