These two primary source readings provide you with the background of the debates over "phlogiston" in the late 18^th century. Priestly, the proponent of phlogiston, and Lavoisier, its opponent stood a the center of the debates over what were to be the underlying chemical building blocks of nature. In essence, it was an argument about what we are to call the "elements" of nature, even though we cannot see them directly. It is about observing effects and inferring causes for those effects (or, more precisely, the matter involved in the causes). Baigrie's introductions to these two readings are quite good and it would replay your time to browse them again.

Notice fist that both extracts deal with very clearly defined experiments in the modern sense: labs, tables upon which the experiments are set, apparatus, chemicals (or at least "ingredients"), and procedures. It is only at this time (last 1/3 of the 18^th century) where the concept of an experiment in the modern sense was really becoming commonplace. Boyle had done them; Newton could not have cared less; most others only did observations, not experiments in the current sense of the word.

Priestley is examining what happened when you burnt things. Fire was the "active" principle in all forms of matter theory, right back to the ancient Greeks, and here it is no different. So, he describes putting one thing after another in a flame, or in a jar with burning glass on it (remember burning ants as a child? - same idea, but less cruel). He works out the details on an idea that had been around for about 100 years, that there were different types of air - and that the air we breathe is some sort of mixture of these types.

Methodologically, what you notice here is a very early development of the hypothetico-deductive method: conjecture, test, confirm or reject. Priestley is just starting at this, of course, but you can see in the last few pages that he has gone beyond simply dumbly observing the experiments, and has started to actively guess what he should find in the next experiments (hence the "hypothetico" part). And in order to do so, he has to have some form of organizing the previous results and making sense of them: that is a theory (hence the "deductive" part [from theory to particular]).

Throughout this selection, you will notice that Baigire ahs added the modern chemical name of the substances that Priestley mentions to the text. We are not yet up to the point where names refer unambiguously to elements and compounds as they do today. The names, however, are or would have been clear to the chemists of the day. People would have known what "marine acid air" was without needing to know that it is what we call gaseous hydrogen chloride (or to have the chemical shorthand or "HCl"). It would be wrong to believe that phlogiston chemists were not doing chemistry, or - worse yet - were doing something that they did not understand. They did do things they understood. They were building a framework - an interpretive framework, if you will - that allowed them to better understand what they were doing and extend their research. That is the essence of science (or at least its ideal), whether working on a theory we now believe to be "correct" or not.

Beyond that, the main ideas to take away are the properties of the various types of air:

• Phlogisticated air: animals die in it, it does not support a burning flame
• De-phlogisticated air: supports respiration and burning
• Inflammable air: air which is heavy in phlogiston and burns violently, but does not support respiration
• Common air: some mixture of the above

And, therefore, the property of Phlogiston: the (elemental) substance which is given off by combustion and respiration; when the air surrounding it is "full" of phlogiston, it cannot hold any more, so combustion or respiration stops (a sort of pressure argument).

Finally, note the last point that Priestley makes: you can measure volumes of gas and infer the proportion of its constituents thereby.

Lavoisier takes Priestley's (and others) work, an takes another step in the process of understanding matter. In effect, he redefines the underlying building blocks in a certain way, based upon his different (although not all that radical) interpretation of standard experiments of the day.

Lavoisier began his work with the definite goal of, as he puts it, reforming the nomenclature of chemistry. Why? Because, he argues, there are too many names for the same thing out there and there are cases where we are not sure that the same name used by two people necessarily was referring to the same thing. You will notice that Lavoisier makes the conscious analogy between chemistry and geometry, and by extension to physics. Here he is interested in giving chemistry the same mechanical, rational, and precise footing as these other sciences - and he in effect did do this.

In the middle of this extract, Lavoisier related the views of a number of other chemists of the day. It is not necessary to link each chemist with an idea (unless covered in lecture), but only to know the range of things that Lavoisier criticized them on.

The last, and largest section of this extract is concerned with Lavoisier's proposals for a new nomenclature and his observations upon the new groupings. Again, it is not important for you to understand each group and its properties. Instead, consider what Lavoisier is doing: he is proposing a grouping such that certain groups have a common characteristic or characteristics to them, and if you can maximize those groups, then Lavoisier reasons, you have a more correct description of nature. Regardless of whether it is more "correct" it is more useful - and often the former is in effect the latter.