TEANSACTIONS OF SECTION B. 587 



ing occluded gases from iron and otlier metals, proves the accuracy of the old' 

 belief that elastic fluids can freely permeate even solid metals. 



We may imagine with what vivid interest Boyle woidd turn, not merely to the 

 results of Priestley's work, but to his methods. Priestley had decomposed litharge 

 with the electric spark, and had satisfied himself in 1774 by heating red lead that 

 the gas he obtained in his earlier experiments was really the one now called oxygen. 



Boyle would see that in the period 1774-7 Lavoisier, being attracted by the 

 ' sceptical chemist's ' own experiment on the heating of lead in closed vessels, over- 

 threw the Phlogistic theory and placed chemistry on a firm basis by showing that 

 the increase in weight of lead and tin, when heated in air, represents exactly the 

 weight of the gaseous body added, and, finally, Dalton having developed the atomic 

 theory and applied it to chemistry, Berzelius made lead memorable by selecting it 

 for the first determination of an atomic weight. 



Withont diverting his attention -from the phenomena of oxidation, Boyle would 

 find questions the interest of which is only equalled by their present obscurity. 

 He would contemplate the most interesting phase of the history of chemical science, 

 described by van 't lioff as that of its evolution from the descriptive to the 

 rational period, in the early days of which the impossibility of separating physics 

 and chemistry became evident, and Boyle would find that chemistry is now 

 regarded from the point of view of the mechanics of the atoms. 



Deville's experiments on dissociation have rendered it possible to extend to the 

 groups of atoms in chemical systems the laws which govern the fusion and 

 vaporisation of masses of matter, and this has produced a revolution comparable 

 in its importance to that which followed the discovery of the law of definite pro- 

 portions, for dissociation has shown us that true causes of chemical change are 

 variations of pressure and of temperature. For instance, oxygen may be prepared 

 on an industrial scale from air by the intervention of oxide of barium heated to a 

 constant temperature of 700°, provided air be admitted to the heated oxide of 

 barium, under a pressure of li atmospheres, while the oxygen, thus absorbed, is 

 evolved if the containing vessel be rendered partially vacuous. It will be evident, 

 therefore, that at a certain critical temperature and pressiu-e the slightest variation 

 of either will destroy the equilibrium of the system and induce chemical change. 



The aim of Boyle's chemical writings was to show that no barrier exists between 

 physics and chemistry, and to ' serve the commonwealth of learning by begetting 

 a good understanding betwixt the chemists and the mechanical philosophers,' who 

 had, as he said, ' been too great strangers to each other's discoveries.' In view of 

 the dominant lines of research which occupy chemists at the present time, such, 

 for instance, as the investigations of ' Osmotic pressure ' and of the application of 

 Boyle's own law to salts in solution, he would ieel that his hope had been realised, 

 and that, though he lived a century too soon to take part in Berthollet's discussion 

 with Proust, he nevertheless shares Berthollet's triumph in the long-delayed but 

 now rapid development of chemistry as a branch of applied mechanics. 



"We need, however, no longer look at these questions from the point of view of 

 Boyle, for our own interest in the application of chemical mechanics to metallurgy 

 is sufficiently vivid, as instances to be given subsequently will show. 



Hitherto I have mainly dwelt on questions relating to oxidation, but not less 

 interesting is the history of the steps by which an accurate knowledge was ac- 

 quired of the other great process practised by the metallurgist, the one to which 

 Paracelsus was the first to apply thQ name of ' Heduction.' Its explanation fol- 

 lowed naturally from the elucidation of the phenomena of combustion by Lavoisier, 

 who in continuation of Macquer's experiments of 1771 proved, in conjunction with 

 other workers, that carbonic anhydride is produced when the diamond is burnt in 

 air or oxygen. Carbon has been known for ages as the most important of the 

 reducing agents, but when, in 1772, Lavoisier heated oxide of lead and carbon 

 together, he did not at first recognise that carbonic anhydride had been produced, 

 simply because the volume of the gas set free was the same as if oxygen merely 

 had been liberated. He soon, however, saw that neither the carbon alone, nor 

 the oxide of lead alone, gave rise to the evolution of carbonic anhydride, which 

 resulted from the mutual action of carbon and a constituent of the litharge. ' This 



