Basics and Discovery of Atmospheric Chemicals - Air Pollution and Global Warming: History, Science, and Solutions - page 12

changes in atmospheric water vapor could be measured
with a hygroscope constructed of dried wool placed
on a scale. A change in weight of the wool over time
would represent a change in the water vapor content
of the air. Capitalizing on Cryfts' notes, Leonardo da
Vinci (1452-1519) drew such a hygroscope in a sketch
that also contained drawings for his Study for the Ado-
ration of the Shepherds (Figure 1.13) and in his Codex
Atlanticus (1481), but using a sponge instead of wool.
Wood and seaweed were later used in place of wool. In
1614, the Italian physician Santorio Santorre invented
the hygrometer, which provided the relative water vapor
content of the air by the contraction or elongation of a
cord or lyre string, which absorbs water vapor. Gut and
hair were used in later hygrometers.

1.2.2.2. Molecular Hydrogen (Gas)
Paracelsus (1493-1541; Figure 1.14), an alchemist
born near Zurich, may have been the first to observe
what is now known as hydrogen gas or molecular
hydrogen [H 2 (g)]. He discovered that when sulfuric

Figure 1.13. Sketch of hygroscope (circular), together
with Study for the Adoration of the Shepherds ,
1478-1480, by Leonardo Da Vinci. Encore Editions,
www.encore-editions.com.

called phosphorus the “ phosphorus of Brand .”
Kunckel published a treatise on phosphorus in 1678.
The light due to phosphorus results from the chemi-
cal reaction of oxygen from the air with the surface of
the phosphorus to create a product that emits visible
radiation. Elemental phosphorus is a component of the
Earth's crust and of soil dust particles.

1.2.2. Studies of Gases in the Air, 1450-1790
Gases were more difficult to observe and isolate than
were liquids or solids, so the study of gases occurred
only after many liquids and solids had been investi-
gated. In this subsection, the history of discovery of
gases from the fifteenth through eighteenth centuries is
discussed.

1.2.2.1. Water Vapor
Although water vapor was known in the ancient world,
changes in its abundance were not detected until the fif-
teenth century. In 1450, Nicolas Cryfts suggested that

Figure 1.14. Paracelsus (1493-1541). Edgar Fahs
Smith Collection, University of Pennsylvania Library.