JMC : The Physical System of St. Thomas / by G.M. Cornoldi, S.J.


A SUBSTANCE that proceeds from the coupling together or combination of elements is called a mixtum, or more commonly a chemical compound. Such for instance is cuniaber, or water -- the one resulting from sulphur and quicksilver, the other from hydrogen and oxygen. The species of the elements of corporeal substances are very few in number, when compared with those of the mixta derived from them, as the letters of the alphabet are very few in comparison with the innumerable words which they compose. We willingly acknowledge that in these days, by means of diligent and repeated experiments, wonderful discoveries have been made about the manifold formation of the mixta: but their essence is passed over very lightly, though deserving particular study.

The mixtum or true chemical compound has a nature specifically different from that of each element of which it is composed; and when this is not verified, the elements cannot be chemically combined, nor can the body resulting from the combination be a mixtum, but may be called an aggregate or a mingled mass. The specific diversity is manifested to us by the constant diversity of their operation, because operari sequitur esse: and this is the only but certain means by which we are able to infer the diversity of the active principle that informs them.

Suppose, for instance, that into an empty vase of glass with the metallic wire in it you introduce oxygen and hydrogen in proportion of volume as one to two, and by the help of the metallic wire strike out the electric spark. There is an instantaneous combustion. The fluids disappear, and little drops of water appear, occupying a space two thousand times less than what was occupied by the oxygen and hydrogen. Now let us consider the mutual relations of these elements to each other and to the water generated from them.

The specific weight of the oxygen is eight times that of the hydrogen at the same temperature. Oxygen will burn, hydrogen will not. Animals inhale oxygen, and not hydrogen. All the specific properties of the one are different from those of the other: and though they have generic properties in common, such as that of being extended, heavy, resistent, the one has positive while the other has negative electricity, and their capacity of heat differs. Their diversity of nature, therefore, could not be more evident. And yet that spark makes all these differences disappear. Instead of the fluids there is one liquid -- water, whose properties have nothing to do with the vanished elements. The specific weight is different and so is the capacity of heat. Though generated from oxygen as much as from hydrogen, it extinguishes fire instead of feeding it. Formed from oxygen and hydrogen, its operation in inorganic things differs widely from theirs, and is different again in plants, in brutes, in man: so that in the operation of water we no more recognize that of oxygen and hydrogen than we recognize the operation of clay in that of gold or silver. Evidently therefore the nature of water differs from that of oxygen and of hydrogen just as the nature of clay differs from the nature of gold or of silver: and therefore the nature of water is specifically different from the nature of the oxygen and of the hydrogen from which it was generated. This holds good of every true mixtum, or chemical compound, in relation to its components.

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