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548 of the Association to collect around him a choice circle of specialists, and in particular to show much attention to Berzelius, who was at that time on a visit to Berlin. Von Humboldt gave a breakfast in honor of Berzelius, which was remarkable for the number of celebrated men who were present at it. After the breakfast a drive was arranged to Humboldt's country-seat at Tegel. Here the host exhibited the art-treasures of his brother William, and afterward the whole party drove to the quarry of Rüdersdorf, where geology was discussed by the learned company. On this occasion, Wöhler has reported that it was very interesting to watch the contrast between Humboldt's well-known inexhaustible powers of conversation and Berzelius's quiet demeanor. Wöhler, being the youngest and slightest in stature, had a seat in a dog-cart between Humboldt and Berzelius. While on the way to the quarry, in the midst of one of Humboldt's harangues, Berzelius turned to Wöhler and said in Swedish: “O Lord, how this man does talk! I can't stand it much longer!” Wöhler was greatly embarrassed for fear that Humboldt would overhear the remark, but, as he kept on talking, this anxiety vanished.

This was, perhaps, the most prolific period of Wöhler's life, for at this time he published his famous researches on aluminum, glucinum, yttrium, and, in association with Liebig, on cyanogen, cyanic and uric acids. Gay-Lussac had proposed the question in the early part of the century whether, when cyanogen was treated with alkalies, a cyanic acid might not be produced, and it was in answer to this question that Wöhler published his first paper in Gilbert's “Annalen” in the year 1822. It was at the same time that Liebig, then a boy in years, had gone to Paris to show Gay-Lussac what he had done in the same direction; and it was Humboldt who aided the boy chemist in Paris, just as he did Wöhler in Berlin in later years. Subsequently, as we have seen, Wöhler and Liebig made common cause of this investigation, and published their researches together. But the most important research of Wöhler falls in the year 1828.

This was the artificial production of urea. This investigation forms an epoch in the history of chemistry. Previous to this time the so-called organic world and the functions of vital force were believed to constitute a realm by themselves. Berzelius had said distinctly in his great text-book that we should never be able to imitate the products of vital force in our laboratories. We could destroy and could build up material things, but to imitate the vital forces would always be impossible. Wöhler, at the age of twenty-eight, overthrew this theory and created a revolution in the domain of chemistry. He made a breach through what appeared to be an impenetrable wall, and this opening has gone on increasing ever since, until it would appear as if, in a few years, no wall would be left standing. Berzelius's estimate of the value of the research on artificial urea is given in a most genial letter which he wrote to Wöhler in January, 1831, and which