1 The Birth of Science - MSRI

5.7 Chemistry 145
andria, in connection with the same phenomenon, but in a more technical
context. After observing that coal, after burning, undergoes a small change
in volume but a large decrease in weight, Heron attributes the drop to the
transformation of coal into particles of different nature (fire, air and earth),
which partly go away as smoke and partly get absorbed by the ground. 91a
Conservation of mass appears to be contradicted in the Pneumatics of
Philo of Byzantium: in the candle experiment (see page 69 and note 85
thereon) the explanation given is that the air “perishes”. But a reading of
the homonymous work by Heron, which was preserved in the original
Greek (unlike Philo’s: see page 68), suggests that this may reflect a simplification
undergone by Philo’s text in the late Arabic and Latin versions
that have reached us. Indeed, Heron, who certainly uses Philo as a source,
repeatedly uses forms of the verb (destroy, spoil, corrupt; probably
the same verb used in Philo’s original) to describe what happens to air
and other substances during combustion, but he always clarifies that the
corruption consists in a transformation into other substances. He says, in
particular, that the air enclosed in a glass container, if consumed by the
fire, is in fact leaving through pores in the glass, leaving behind empty
space that attracts other matter. 91b Thus conservation of matter was regarded
by Heron as so certain that its apparent violations were explained
by means of invisible processes. It is highly improbable that this view was
a novelty of Heron’s times, if we consider that Erasistratus, in the third
century B.C., also seems to have been so confident in the conservation of
matter as to deduce from the change in weight of an animal left in isolation
the emission of invisible matter (see the description of his experiment
on page 134).
Some additional information about ancient chemical knowledge can be
gleaned from papyri. An especially interesting case is that of the word oxos
(). It is usually translated as vinegar, that being its original meaning.
But recipe 14 of the Leyden papyrus talks about oxos from the purification
of gold ( ¥ ). Since the methods given for purifying
gold may have released hydrochloric or sulfuric acid but certainly
not wine vinegar, it is clear that oxos is being used here in a sense similar
to acid, a notion that must have been partly worked out by Alexandrian
empirical chemists. The Latin term corresponding to oxos is acetum, also
translated as vinegar. Now, Livy says that Hannibal used acetum to dissolve
a blockage in a gorge. 92 This is unlikely (and Polybius says nothing page 189
of the sort in his account), but it is very suggestive: Livy may have heard
91a Heron, Pneumatica, I, proem = [Heron: OO], vol. I, 10, 13–24.
91b Heron, Pneumatica, I, proem = [Heron: OO], vol. I, 16, 10–14.
92 Livy, Ab urbe condita libri, XXI, xxxvii, 2.
Revision: 1.9 Date: 2002/09/14 19:12:01