The Story of Alchemy and the Beginnings of Chemistry

by M. M. Pattison Muir

Priestley thought of properties in much the same way as the alchemists thought of them, as wrappings, or coverings of an essential something, from which they can be removed and around which they can again be placed. The protean principle of phlogiston was always at hand, and, by skilful management, was ready to adapt itself to any facts. Before the phenomena of combustion could be described accurately, it was necessary to do two things; to ignore the theory of phlogiston, and to weigh and measure all the substances which take part in some selected processes of burning.

Looking back at the attempts made in the past to describe natural events, we are often inclined to exclaim, "Why did investigators bind themselves with the cords of absurd theories; why did they always wear blinkers; why did they look at nature through the distorting mists rising from their own imaginations?" We are too ready to forget the tremendous difficulties which beset the path of him who is seeking accurate knowledge.

"To climb steep hills requires slow pace at first."

Forgetting that the statements wherein the men of science of our own time describe the relations between natural events are, and must be, expressed in terms of some general conception, some theory, of these relations; forgetting that the simplest natural occurrence is so complicated that our powers of description are incapable of expressing it completely and accurately; forgetting the uselessness of disconnected facts; we are inclined to overestimate the importance of our own views of nature's ways, and to underestimate the usefulness of the views of our predecessors. Moreover, as naturalists have not been obliged, in recent times, to make a complete renunciation of any comprehensive theory wherein they had lived and moved for many years, we forget the difficulties of breaking loose from a way of looking at natural events which has become almost as real as the events themselves, of abandoning a language which has expressed the most vividly realised conceptions of generations of investigators, of forming a completely new mental picture of natural occurrences, and developing a completely new language for the expression of those conceptions and these occurrences.

The younger students of natural science of to-day are beginning to forget what their fathers told them of the fierce battle which had to be fought, before the upholders of the Darwinian theory of the origin of species were able to convince those for whom the older view, that species are, and always have been, absolutely distinct, had become a matter of supreme scientific, and even ethical, importance.

A theory which has prevailed for generations in natural science, and has been accepted and used by everyone, can be replaced by a more accurate description of the relations between natural facts, only by the determination, labour, and genius of a man of supreme power. Such a service to science, and humanity, was rendered by Darwin; a like service was done, more than three-quarters of a century before Darwin, by Lavoisier.

Antoine Laurent Lavoisier was born in Paris in 1743. His father, who was a merchant in a good position, gave his son the best education which was then possible, in physical, astronomical, botanical, and chemical science. At the age of twenty-one, Lavoisier gained the prize offered by the Government for devising an effective and economical method of lighting the public streets. From that time until, on the 8th of May 1794, the Government of the Revolution declared, "The Republic has no need of men of science," and the guillotine ended his life, Lavoisier continued his researches in chemistry, geology, physics, and other branches of natural science, and his investigations into the most suitable methods of using the knowledge gained by naturalists for advancing the welfare of the community.

In Chapter VI., I said that when an alchemist boiled water in an open vessel, and obtained a white earthy solid, in place of the water which disappeared, he was producing some sort of experimental proof of the justness of his assertion that water can be changed into earth. Lavoisier began his work on the transformations of matter by demonstrating that this alleged transmutation does not happen; and he did this by weighing the water, the vessel, and the earthy solid.

Lavoisier had constructed for him a pelican of white glass (see [Fig. XI., p. 88]), with a stopper of glass. He cleaned, dried, and weighed this vessel; then he put into it rain-water which he had distilled eight times; he heated the vessel, removing the stopper from time to time to allow the expanding air to escape, then put in the stopper, allowed the vessel to cool, and weighed very carefully. The difference between the second and the first weighing was the weight of water in the vessel. He then fastened the stopper securely with cement, and kept the apparatus at a temperature about 30° or 40° below that of boiling water, for a hundred and one days. At the end of that time a fine white solid had collected on the bottom of the vessel. Lavoisier removed the cement from the stopper, and weighed the apparatus; the weight was the same as it had been before the heating began. He removed the stopper; air rushed in, with a hissing noise. Lavoisier concluded that air had not penetrated through the apparatus during the process of heating. He then poured out the water, and the solid which had formed in the vessel, set them aside, dried, and weighed the pelican; it had lost 17-4/10 grains. Lavoisier concluded that the solid which had formed in the water was produced by the solvent action of the water on the glass vessel. He argued that if this conclusion was correct, the weight of the solid must be equal to the loss of weight suffered by the vessel; he therefore separated the solid from the water in which it was suspended, dried, and weighed it. The solid weighed 4-9/10 grains. Lavoisier's conclusion seemed to be incorrect; the weight of the solid, which was supposed to be produced by the action of the water on the vessel, was 12 1/2 grains less than the weight of the material removed from the vessel. But some of the material which was removed from the vessel might have remained dissolved in the water: Lavoisier distilled the water, which he had separated from the solid, in a glass vessel, until only a very little remained in the distilling apparatus; he poured this small quantity into a glass basin, and boiled until the whole of the water had disappeared as steam. There remained a white, earthy solid, the weight of which was 15 1/2 grains. Lavoisier had obtained 4 9/10 + 15 1/2 = 20 2/5 grains of solid; the pelican had lost 17 2/5 grains. The difference between these weights, namely, 3 grains, was accounted for by Lavoisier as due to the solvent action of the water on the glass apparatus wherein it had been distilled, and on the glass basin wherein it had been evaporated to dryness.

Lavoisier's experiments proved that when distilled water is heated in a glass vessel, it dissolves some of the material of the vessel, and the white, earthy solid which is obtained by boiling down the water is merely the material which has been removed from the glass vessel. His experiments also proved that the water does not undergo any change during the process; that at the end of the operation it is what it was at the beginning—water, and nothing but water.