It was through the Chemical Revolution of the late eighteenth century that water fi rst came to be recognized as a compound, having been considered an element since ancient times. In this chapter I offer a revisionist account of that...
moreIt was through the Chemical Revolution of the late eighteenth century that water fi rst came to be recognized as a compound, having been considered an element since ancient times. In this chapter I offer a revisionist account of that momentous event. A systematic appraisal shows that the old phlogistonist system of chemistry was not clearly inferior to Lavoisier's oxygenist system of chemistry. Lavoisier's system actually suffered from signifi cant empirical and theoretical problems already recognized at the time, and there was signifi cant methodological incommensurability between the two systems, though only mild semantic incommensurability. Aside from the effective and ruthless campaigning by the Lavoisierians, the demise of phlogiston (which was not as sudden or complete as often imagined) was most of all due to the advent of compositionism as a dominant trend in chemistry, into which phlogistonist practices did not easily fi t. With the demise of phlogiston, many valuable elements of knowledge were lost; in effect, these were recovered and developed later with the help of different concepts (e.g., potential energy and electrons), but I argue that it would have been better for science if the phlogistonist system had been allowed to continue its work. This conclusion also anticipates the more general argument for pluralism in science, to be given fully in Chap. 5. In order to give more precision in the articulation and defence of these ideas, I introduce and use the notion of system of practice as a unit of analysis. 1.1 The Premature Death of Phlogiston In the middle of the eighteenth century people still considered water as an element. For Europeans this idea dated at least back to the ancient Greeks at the time of Aristotle, according to whom water was one of the four basic elements (along with earth, air and fi re) which constituted all the substances making up the terrestrial world. Thales had even postulated that water was the element from which everything was made. We now know that water is not an element, but a compound made Chapter 1 Water and the Chemical Revolution 1.1 The Premature Death of Phlogiston Kinds of Air (1774, 1790) is a sheer delight for those who share a sense of fascination about all the diverse phenomena of nature and a childlike wonder at our own ability to call them forth. Priestley was the fi rst person to make and bottle what we now call oxygen and tell the wide world about it. In Carl Djerassi and Roald Hoffmann's amusing play Oxygen (2001) , it is left uncertain who should win the fi rst "Retro-Nobel Prize" in Chemistry for the discovery of oxygen. But those authors, or anyone else well enough informed, would not deny Priestley's priority over Carl Wilhelm Scheele (1742-1786) in publication, and over Antoine-Laurent Lavoisier (1743-1794) in deed. Priestley's excitement is palpable as he reports, in his letter of 15 March 1775 to James Pringle, the President of the Royal Society of London: "the most remarkable of all the kinds of air that I have produced. .. is one that is fi ve or six times better than common air, for the purpose of respiration, infl ammation, and, I believe, every other use of common atmospherical air." First he tested this new air by burning things in it. And then, "to complete the proof of the superior quality of this air, I introduced a mouse into it; and in a quantity in which, had it been in common air, it would have died in about a quarter of an hour, it lived, at two different times, a whole hour, and was taken out quite vigorous." (Priestley 1775 , 387-388) After that he found the courage to breathe the new air himself. "The feeling of it in my lungs," Priestley reported, "was not sensibly different from that of common air, but I fancied that my breast felt peculiarly light and easy for some time afterwards. Who can tell but that in time, this pure air may become a fashionable article in luxury. Hitherto only two mice and myself have had the privilege of breathing it." On the new site of the Mill Hill Chapel in Leeds, for which he preached for several years during his scientifi c heyday, a blue plaque proudly proclaims (Fig. 1.1): "Joseph Priestley, discoverer of oxygen, was minister here 1767-1773." Such commemoration would have annoyed Priestley, for he did not call his new gas "oxygen". He called it "dephlogisticated air", and that was not just a matter of words. By that phrase he really meant common air cleansed of the "phlogiston" that is normally mixed up in it. What was phlogiston? In short, it was the principle of infl ammability; "principle" here did not mean a fundamental rule, but rather a fundamental substance that combined with other substances and gave them its characteristic properties. Phlogiston was the principle that imparted combustibility to combustibles. A combustible substance was rich in phlogiston, and when it burned it released its phlogiston, which then manifested itself in the fl ame that came out. Certain experiments seemed to indicate that metals, too, were rich in phlogiston, and that it was phlogiston that gave them the characteristic metallic properties, such as their shiny luster, their malleability and ductility, and their electrical conductivity (and their infl ammability actually, under the right circumstances). When a metal was deprived of phlogiston, it lost its key metallic properties and became an earthy substance called "calx" (which we would now identify as rust or oxide). All of this sounds much too fanciful to our modern ear. Let us see if we can make the phlogistontheorist to see some common sense. If calx is really metal that has lost its phlogiston, then you should be able to turn it back into metal by giving some phlogiston to it. Can you do that? "Sure", says the phlogistonist. That is what smelters have been doing for 84 This was set up by Lavoisier and colleagues against the phlogistonist Journal de physique of Delamétherie. Crosland (1994) is the most extensive source; see also Court (1972). 85 Donovan (1993) and Poirier (1996) gives good accounts of Marat's role.