Electronic computers can do many things. They have been taught to play chess, to forecast the weather, to find out what is happening in the depths of distant stars, to carry out calculations involving unthinkable difficulties. All one has to know is how to assign their programme of operations.

Electronic computers are now finding more and more usage in chemistry too. Great automatic plants are controlled by these machines. With their aid, investigators learn everything about numerous chemical processes before putting them into practice.

But chemists have at their disposal a rather unusual �electronic computer.� It was invented about a hundred years ago before the term electronic computer ever appeared in the languages of the world.

This remarkable machine is the Periodic System of Elements. It enables scientists to do what even the most daring investigators would not risk doing before. The Periodic System made it possible to predict the existence of elements yet unknown, undiscovered even in the laboratory. And not only to predict them, but even to describe their properties. It could tell whether they would be metals or non�metals, heavy like lead, or light like sodium, and in what terrestrial ores and minerals the unknown elements were to be sought.

The answers to all these questions were supplied by the �electronic computer� invented by Mendeleyev.

In 1875 the French scientist Paul Emile Lecoq de Boisbaudran made an important report to his colleagues. He had succeeded in detecting an admixture of a new element in a zinc ore, a tiny grain weighing not more than a gram. Being an experienced investigator, he studied the properties of gallium (such was the name of the �newborn� element) in all their aspects, and wrote a paper about them.

Some time passed and the post brought de Boisbaudran an envelope bearing a St. Petersburg postmark. In the brief letter the French chemist read that his correspondent agreed in full with his results, except for one detail: the specific gravity of gallium should be 5.9 instead of 4.7. The letter was signed: D. Mendeleyev.

Lecoq de Boisbaudran was worried. Had the Russian titan of chemistry anticipated him in the discovery of the new element?

No, Mendeleyev had not had gallium in his hands. He had simply made efficient use of the Periodic System.

Mendeleyev had long since known that sooner or later an unknown element would be found to take the place in the table, which was now occupied by gallium. He had given it the preliminary name of eka-aluminium and had predicted its chemical nature very accurately, knowing the properties of its neighbours in the Periodic Table.

So Mendeleyev became the first �programmer� in chemistry. He predicted almost a dozen other then unknown elements, and described their properties more or less completely. Their present names are: scandium, germanium, polonium, astatine, hafnium, rhenium, technetium, francium, radium, actinium, and protactinium. Most of them had actually been discovered by 1925.

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