as not long since Hales had
pronounced air to be a chaotic mixture of effluvia. Black showed that
common air contains a small amount of fixed air, and that fixed air
must be considered as a fluid differing in many of its properties
from common air, especially in its being absorbed by quicklime and by
alkalies. It must be remembered that at that time carbon was not
recognised as an element; and hence, though Black knew that fixed air
was a product of the combustion of charcoal, he did not attribute it
to the union of carbon with oxygen, although the sentence quoted above
closely approaches to the truth.

The discovery of nitrogen was next in the order of time. It was made by
Daniel Rutherford, a pupil of Black’s, and at his instigation, and its
description formed a thesis for his degree of Doctor of Medicine.

Daniel Rutherford was born at Edinburgh on November 3rd, 1749. He was
the son of a medical man, Dr. John Rutherford, one of the founders
of the Medical School in that city. He was educated at Edinburgh
University, and after graduating in Arts, became a medical student,
taking his degree of M.D. in 1772. His diploma was obtained on 12th
September. He then travelled for three years in England, France, and
Italy, and in 1775 he returned to his native town, where he practised
his profession. In 1786 he succeeded Dr. John Hope in the Chair of
Botany in his University, but he did not on that account resign his
practice. He was president of the Royal College of Physicians of
Edinburgh from 1796 to 1798. During the greater part of his life he
suffered from gout; he died in 1819, at the age of seventy.

Rutherford does not seem to have pursued the study of chemistry
further: his duties led him into other fields. His genial, pleasant
face, seen in the portrait by Raeburn, shows him to have possessed a
happy disposition; and he is said to have maintained until his death
his friendship with Black, and his interest in the progress which
science was then rapidly making.

The title of Rutherford’s dissertation, of whic