TRANSACTIONS OF SECTION B, 641 



a communicatiou on liquid diffusion, in which he ' gave a view of some of the 

 unpublished results, to ascertain whether solutions of saline bodies hpd a power 

 of diffusion among liquids, especially water.' In 1877 Pfeffer, who, like de Vries, 

 entered the field from the botanical physiological side, succeeded in effecting the 

 measui'ement of osmotic pressure. Ten years later van 't Hoff formulated the 

 modern dissociation theory of solution by applying to dissolved substances the 

 laws of Boyle, Gay-Lussae, and Avogadro, the law of osmotic pressure, and 

 Raoult's law connecting the depression of freezing point with molecular weight, 

 thus laying the foundation of a doctrine which, whether destined to survive in 

 its present form or not, has certainly exerted a great inffuence on contemporary 

 chemical thought. 



Consider, further, the state of knowledge in 1851 concerning such leading prin- 

 ciples as dissociation or thermolysis, mass action, and chemical equilibrium. 

 Abnormal vapour densities had been observed by Avogadro in 1811, and hy 

 Ampere in 1814. Grove had dissociated water vapour by heat in 1847, but the 

 first great advance was made ten years later by Saiute-Claire Deville, from whoso 

 work has emanated our existing knowledge of this subject. I may add that the 

 application of this principle to explain the cases of abnormal vapour density was 

 made in 1858 by Kopp, Kekule, and Cannizzaro almost simultaneously ; but, 

 strangely enough, this explanation was not accepted by Deville himself. The 

 subsequent stages are subjects of modern history The current views on mass 

 action were foreshadowed, as is well known, by Berthollet in his ' Statique 

 Chimique,' published in 1803, but no great advance bad been made when the 

 British Association last met here. The subject first began to assume a quanti- 

 tative aspect through the researches of Bunsen and Debus in 1853, and was 

 much advanced by Gladstone in 1865, and by Harcourt and Esson a year later. 

 Guldberg and Waage published their classical work on this subject in 18G7. 



Equally striking will appear the advances made since 1851 if we consider 

 that the whole subject of spectrum analysis, which brings our science into rela- 

 tionship with astronomy, has been called into existence since that date. The cele- 

 brated work of Bunsen and KircbhofF was not published till 1859. Neither can 

 I refrain from reminding you that the coal-tar colour industry, with which I 

 have been to a small extent connected, was started into activity by Perkin's dis- 

 covery of mauve in 1856 ; the reaction of this industry on the development of 

 organic chemistry is now too well known to require further mention. In that 

 direction also which brings chemistry into relationship with biology the progress 

 has been so great that it is not going beyond the fact to state that a new science 

 has been created. Pasteur began his studies on fermentation in 1857, and out 

 of that work has arisen the science of bacteriology, with its multifarious and far- 

 reaching consequences. As this chapter of chemical history forms the subject 

 of one of the evening discourses at the present meeting, it is unnecessary to dwell 

 further upon it now. One other generalisation may be chronicled among the 

 great developments achieved since 1851, I refer to the periodic law connecting 

 the atomic weights of the chemical elements with their physical and chemical 

 properties. Attempts to establish numerical relationships in the case of isolated 

 groups of elements had been made by Dobereiner in 1817, by Gmelin in 1826, 

 and again by Dobereiner in 1829. The triad system of grouping was further 

 developed by Dumas in 1851. I am informed by Dr. Gladstone that at the last 

 Ipswich meeting Dumas' speculations in this direction excited much interest. 

 All the later steps of importance have, however, been made since that time, viz., 

 by de Chancourtois in 1862, the 'law of octaves' by Newlands in 1864, the 

 periodic law by Mendeleelf, and almost contemporaneously by Lothar Meyer in 

 1869. 



I have been tempted into giving this necessarily fragmentary and possibly 

 tedious historical sketch because it is approaching half a century since the British 

 Association visited this town, and the opportunity seemed favourable for going 

 through that process which in commercial afi'airs is called 'taking stock.' The 

 result speaks for itself. Our students of the present time who are nourished 

 intellectually by these doctrines should be made to realise how rapid has been 

 1895. T T 



