What elements were “known” to alchemists/chemists around the time of Lavoisier? Wikipedia’s article on Lavoisier mentions that Lavoisier studied the composition of water and air, “which at the time were considered elements.” What other “elements” did alchemists/chemists of his time think were elements (both correctly and incorrectly)?
How did they decide something was an element pre-Lavoisier? I know the definition was basically “something which can’t be decomposed into other substances,” but how could they decide whether something broke down or not without Lavoisier’s careful weighing? For example, if they heated copper in air, how did they decide that copper was reacting with air to form copper oxides, and not that things were be driven out of copper to form an element?
I feel like I should know these things, but I can’t find the answers…
i actually had to do a paper on this for a chemistry class. there is a great article on the university websites journal database, but you need a password to get in. i’ll look for the article elsewhere.
The problem is, the second list isn’t true, in the way I was looking for. The Greeks knew about iron, but they had no idea that it was an element. Saying it was known since antiquity is misleading. When did someone figure out that it was an element? How did they figure that out?
You’re right to be suspicious about the Wikipedia list. Lavoisier’s notions loom so large in subsequent conceptions that there’s always the danger that they are read back into earlier findings. As a non-expert on 18th century chemistry, it strikes me that it’s difficult to get a clear picture of exactly what the nuances were in what is now often assumed to be people talking about elements in the sense that we now think of them.
There had, at least since classical times, always been people suggesting sets of elements, with the Aristolean foursome of earth, air, fire and water long having been the most popular. But other versions had been suggested. The most famous modern, but pre-Lavoisier, analysis of these ideas had been Boyle’s Sceptical Chymist, back in 1677. (I’m mildly surprised that the whole text of the book isn’t online.) Boyle laid into the supporters of Aristotle, together with those of the main competing idea: that there weren’t elements, but three “principles”, usually salt, sulpher and mercury. While he finds all these ideas wanting, the book isn’t merely an attack, since Boyle also thrashes around the subject of defining what an “element” might actually be, but doesn’t quite propose a final definition. As far as I can tell, neither does he actually point to any substance that he considers obviously has to fit any definition.
Another influential pre-Lavoisier theorist was Georg Stahl. I haven’t read any of his stuff and there’s some disagreement in secondary accounts about exactly what his ideas were. For instance, I’ve seen it suggested that he proposed four elements: phlogiston, water, mercury and a type of earth. On the other hand, the more detailed accounts of Stahlian chemistry I’ve read see his thinking as more along “principle” lines. Thus an emphasis on underlying properties rather than underlying substances. To complicate matters, I’ve also seen it suggested that there’s a gradual shift over the 18th century from notions of principles - which aren’t elements but which gradually become more material as properties are tied to different chemicals - to Lavoisier’s elements.
Then there’s the complicated case of Priestley. In 1776, he wrote:
That seems to nicely confirm the suggestion that water and air “at the time were considered elements.” Except that Priestley probably didn’t believe in elements at all. He had a more Stahlian vision, which was materialist and atomistic, yet avoided identifying anything seen in the lab as fundamental. Scientists could explain their results in terms of properties, but what the world was made of was something deeper - and infused with God. (There’s also the caveat about the passage I quoted above that he goes on to argue that air isn’t that uncomplicated. I half suspect he was setting up a straw man.)
So it’s not obvious to me that was any concensus about what were elements and what weren’t prior to Lavoisier’s proposals. Some people had ideas that were sort of like what we’d now think of as elements, but others disagreed with even the whole idea.
Lavoisier’s comments about his predecessors in the Traité élémentaire de Chimie are worth quoting. From the preface (in Kerr’s 1790 translation):
There’s a degree to which this may be misleading, since, as I’ve said, it’s not obvious to me that all these ideas can be lumped together as about the same idea of “element”. Lavoisier may himself be an example of someone projecting his concept back into the past.
For completeness, Lavoisier’s list of elements can be found midway down that last link. Some of the relevant related texts can be found on the same site.
It should also be said that, once proposed, Lavoisier’s definitions and names seem to have caught on very quickly.
It wasn’t necessarily terribly obvious at the time. Even when you did weigh them.
The classic example is Priestley and “dephlogisticated air”. Having identified this, he did a series of careful experiments to determine its weight, with the result that he found that dephlogisticated air was heavier than the phlogisticated sort. Since the whole idea was that phlogiston was some sort of substance that had been removed from the air, this might appear to be a problem. Others had encountered similar results in other cases and there were various explanations, including the suggestion that phlogiston had a negative weight. In his report on the experiments, Priestley simply avoided discussing the significance of this part of his results. But we know from elsewhere in his writings that he argued, for various essentially metaphysical reasons, that weights in chemical reactions weren’t a particularly fundamental notion and so too much could be read into them.
Thank you very, very much, bonzer. That gives me exactly what I need. I’m writing an intro to a piece about Lavoisier and Dalton (among other things, but that’s what I’m focusing on right now), and I wanted something about the state of classification of matter before the law of conservation of mass and Dalton’s theory came on the scene. The story actually works better, I think, if the situation was rather confused than if there were a set list of elements and a set way of defining them.
I’ll definitely be doing some more reading to make sure I grok as completely as possible what was going on at the time, but you’ve pointed me to the right places, I think.
