Urea Analysis

From WikidChem

Wöhler did not have to analyze urea, because it had already been done by a British amateur chemist, Dr. Prout, who also analyzed urea. All Wöhler had to do was calculate a theoretical analysis for ammonium cyanate with Berzeleus' atomic weights and compare with Prout's experimental results. Prout's numbers were so good, in fact, that he subsequently acquired great fame among historians as one of the premiere analytical chemists of his time.

If we compare Prout's numbers with the modern numbers we have with today's technology, his numbers become even more impressive because of how close they are to the actual numbers. His numbers, however, are too good, because his "experimental" number for nitrogen is 100 times more precise than would be justified on the basis of his experimental measurements. (See Prout's apparatus)

This leads to questions about how Prout actually obtained his numbers. He obtained these numbers with his own theory of atomic weights. He believed that all of the elements were made up of combinations of protyles, which were the basic hydrogen atoms (e.g. carbon would be 6 protyles, oxygen 8, etc.). Using this theory, he "corrected" his approximated experimental results without saying so. By good fortune his theoretical numbers were better than Berzeleus' hard-earned experimental numbers. Prout got lucky because his theory happened to work very well in this particulr case.

This slide also points out the interesting fact that even the most accomplished chemists make mistakes. Wöhler's numbers did not sum to 100 because he truncated the numbers while adding. The slides also expose certain dislectic errors that went unchecked even in the works of such great scientists as Prout and Wöhler.