Theory phlogistic

Salt formation as a criterion for an acid-base interaction has a long history (Walden, 1929). Rudolph Glauber in 1648 stated that acids and alkalis were opposed to each other and that salts were composed of these two components. Otto Tachenius in 1666 considered that all salts could be broken into an acid and an alkali. Boyle (1661) and the founder of the phlogistic theory, Stahl, observed that when an acid reacts with an alkali the properties of both disappear and a new substance, a salt, is produced with a new set of properties. Rouelle in 1744 and 1754 and William Lewis in 1746 clearly defined a salt as a substance that is formed by the union of an acid and a base. 

Chemistry as distinct from Alchemy and iatro-chemistry commenced with Robert Boyle (see plate 15), who first clearly recognised that its aim is neither the transmutation of the metals nor the preparation of medicines, but the observation and generalisation of a certain class of phenomena who denied the validity of the alchemistic view of the constitution of matter, and enunciated the definition of an element which has since reigned supreme in Chemistry and who enriched the science with observations of the utmost importance. Boyle, however, was a man whose ideas were in advance of his times, and intervening between the iatro-chemical period and the Age of Modem Chemistry proper came the period of the Phlogistic Theory — a theory which had a certain affinity with the ideas of the alchemists. 

That he might bring into one point of view, and compare the various changes effected by the agency of fire, Stahl invented a new Principle, which he named Phlogiston, and constructed an hypothesis which is generally known as the phlogistic theory. He explained, and applied, this hypothesis in various books, especially in one published at Halle in 1717. 

In addition to these advantages, the phlogistic theory was based on experiments, and led to experiments, the results of which proved that the capacity to undergo combustion might be conveyed to an incombustible substance, by causing it to react with some other substance, itself combustible, under definite conditions. The theory thus prepared the way for the representation of a chemical change as an interaction between definite kinds of substances, marked by precise alterations both of properties and composition. 

Priestley was a thorough-going phlogistean. He seems to have been able to describe the results of his experiments only in the language of the phlogistic theory just as the results of most of the experiments made to-day on the changes of compounds of the element carbon cannot be described by chemists except by making use of the conceptions and the... 

The experimental study of combustion made by Lavoisier proved the correctness of that part of Stahl s phlogistic theory which asserted that all processes of combustion are very similar, but also proved that this likeness consists in the combination of a distinct gaseous substance with the material undergoing combustion, and not in the escape therefrom of the Principle of fire, as asserted by the theory of Stahl. After about the year 1790, it was necessary to think of combustions in the air as combinations of a particular gas, or air, with the burning substances, or some portions of them. 

The most influential development of chemical theory of the eighteenth century was the phlogistic theory which attempted to explain and to correlate the phenomena of combustion, oxidation and reduction in a relatively simple and comprehensive maimer. The credit of founding this theory and of attracting the attention of chemists to it is due to Stahl. 

Macquer was not, indeed, the first to introduce the phlogistic theory into France. Several prominent chemists and teachers had adopted it in their philosophy. Such were Stephen Geoffroy (1672-1731), Duhamel de Morveau (1700-1781), and Guillaume Francois Rouelle (1703-1770). Yet, by common consent Macquer is considered the most prominent and most enthusiastic French advocate of the phlogistic philosophy. Macquer was born in Paris of Scotch ancestry, followers of the Stuarts who migrated to France on the expulsion of that dynasty. The original Scotch... 

It is manifest from Lavoisier s treatise that while skeptical as to the phlogistic theory, which he alludes to as... 

All these eighteenth century investigators expressed their views on the action of air and combustion in terms of the phlogistic theory of Becher and Stahl, and it remained for Antoine-Laurent Lavoisier, the French savant, who fell a victim to the guillotine in 1794, to free them from this incubus and to develop the new theory wherein oxygen was assigned its proper role as a constituent of air and a supporter of combustion. 

With the fall of the phlogistic theory, however, the term dephlogisticated air became untenable and Chaptal in 1791 suggested nitrogen, since it is a constituent of nitre. 

After establishing chemistry on its modern course following the demise of the phlogistic theory of matter, chemists of the late eighteenth century and early nineteenth century turned their attention to formulating laws and theories governing chemical reactions. Some of these laws and theories are briefly outlined below. 

Carbon played an important role in the progress of the phlogistic theory. According to this theory carbon was not a simple substance but pure phlogiston. By studying combustion of coal and other compounds, A. Lavoisier was the first to show that carhon is a simple substance. Here we are going to digress a little from the story about how carhon found its identity. 

---