Page:Popular Science Monthly Volume 79.djvu/99

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95
JACOBUS HENRICUS VAN'T HOFF

JACOBUS HENRICUS VAN'T HOFF
By Professor HARRY C. JONES
JOHNS HOPKINS UNIVERSITY

THE death of Van't Hoff removes one of the leading men of science not only of this age, but of all time.

Born in Rotterdam in 1852, the son of a physician, he received his early training in the Bealschule in Rotterdam and in the Polytechnikum in Delft. At twenty he had completed his work in the University of Leiden. He then studied under Kekulé in Bonn and Würtz in Paris, and obtained the Doctor's degree at Utrecht, at the age of twenty-two.

Van't Hoff, in 1876, was appointed privatdozent in physics in the veterinary college in Utrecht. In 1877 he was called to Amsterdam as lecturer in chemistry, and was appointed professor of chemistry in 1878, a position which he held until 1896, when he accepted a call to a chair created for him at Berlin. He held this chair and was also a member of the Berlin Academy of Sciences until his death on March 1, 1911.

Van't Hoff did three great things. His early work was with Mulder in Utrecht, Kekulé in Bonn and Würtz in Paris, and therefore, in organic chemistry. He raised and answered the question, what is the arrangement in three dimensions in space of the atoms in the simpler compounds of carbon? Henri had shown that the four hydrogen atoms in marsh gas (CH4) all bear the same relation to the molecule. The geometrical configuration of this molecule follows of necessity from this fact. The only geometrical form in three dimensions in space fulfilling the condition of a central object surrounded symmetrically by four things of the same kind, is the regular tetrahedron. Thus arose the theory of the "tetrahedral carbon atom."

Some compounds of carbon rotate the beam of polarized light to the right, others to the left—are "optically active," as they are termed. Pasteur had pointed out that this is possible only in compounds in which there is some kind of asymmetry. Van't Hoff showed in what the asymmetry consisted. He showed that all optically active compounds of carbon then known contain a carbon atom in combination with four different atoms or groups, and the same holds true to-day. Such a carbon atom is known as an "asymmetric carbon atom," and thus arose the theory of the "asymmetric tetrahedral carbon atom,"