ADDBESS. 43 



sense) in the world ; then all the energy available will have become dis- 

 sipated, and we shall have arrived at a condition of things from which 

 there is no apparent escape. This is what is called the ' Dissipation of 

 Energy.' 



Prof. Frankland has been so good as to draw up for me the following' 

 account of the progress of Chemistry diii-ing the last half-century. 



Most of the elements had been discovered before 1830, the majority 

 of the rarer elements since the beginning of the century. In addition to 

 these the following five have been discovered, three of them by Mosander, 

 viz.: — lanthanum in 1839, didj-mium in 1842, and erbium in 1843. 

 Ruthenium was discovered by Glaus in 1843, and niobium by Rose in 

 1844. Spectrum Analysis has added five to the list, viz.: — Caesium and 

 rubidium, which were discovered by Bunsen and Kirchhoffin 1860; thal- 

 lium, by Crookes in 1861 ; indium, by Reich and Richter in 1863 ; and 

 gallium, by Lecoq de Boisbaudran in 1875. 



As regards theoretical views, the atomic theory, the foundation of 

 scientific chemistry, had been propounded by Dalton (1804-1808). The 

 .three laws which have been chiefly instrumental in establishing the true 

 atomic weights of the elements — the law of Avogadro (1811), that equal 

 volumes of gases under the same conditions of temperature and pressure 

 contain equal numbers of molecules ; the law of Dulong and Petit (1819), 

 that the capacities for heat of the atoms of the various elements are 

 equal; and Mitscherlich's law of isomorphism (1819), according to which 

 equal numbers of atoms of elements belonging to the same class may 

 replace each other in a compound without altering the crystalline form 

 of the latter, had been enunciated in quick succession ; but the true ap- 

 plication of these three laws, though in every case distinctly stated by 

 the discoverers, failed to be generally made, and it was not till the rectifi- 

 cation of the atomic weights by Cannizzaro, in ] 858, that these important 

 discoveries bore fruit. 



In organic chemistry the views most generally held about the year 

 1830 were expressed in the radical theory of Berzelius. This theory, 

 which was first stated in its electro-chemical and duahstic form by its 

 author in 1817, received a further development at his hands in 1834 

 after the discovery of the benzoyl-radical by Liebig and Wohler. In the 

 same year (1834), however, a discovery was made by Dumas, which was 

 destined profoundly to modify the electro- chemical portion of the theory, 

 and even to overthrow the form of it put forth by Berzelius. Dumas 

 showed that an electro-negative element, such as chlorine, might replace, 

 atom for atom, an electro-positive element like hydrogen, in some cases 

 without much alteration in the character of the compound. This law of 

 substitution has formed a necessary portion of every chemical theory 

 which has been proposed since its discovery, and its importance has 

 increased with the progress of the science. It would take too long to 

 enumerate all the theoretical views which have prevailed at various times 



