36 KiiPOKT— 1875. 



auy portion of matter are in constant rapid motion, Taut that the atoms which con- 

 stitute each molecule are similarly moving to and fro. Such movement might be 

 an oscillation about the position assigned to the several atoms in the constitutional 

 formula of the molecule. Since, however, the modes of formation and decompo- 

 sition of substances are the principal facts upon which their formulae are based, it 

 is to be considered whether these facts may not depend altogether upon the nature 

 or average nature of the motion impressed upon the atoms — that is, upon dynamical 

 and not upon statical differences. 



Many substances are known whose existence is contrary to the theory of 

 valency and saturation, such as nitric oxide and carbonic oxide; others which 

 transgress the theory of isomerism, such as chloride of dichlordibromethane 

 (C CP Br-, CP) and bromide of tetrachlorethane (C" CV, Br'), which should be 

 identical, but are isomeric * : yet these theories are simply an expression of the state- 

 ment that certain substances can exist or can differ, while others cannot. It is true 

 that in the vast majority of cases the theoretical limitation seems to hold good. 

 But just as the absence of any fossil remains of the connecting links between 

 species is only significant if the geologic search has been sufficiently thorough, so 

 it is with chemical theories depending upon the non-existence of certain classes of 

 bodies. Indeed, in om- case, where investigation is guided by theory, and, as a 

 rule, only those things which are looked for are found, the limitation may be 

 partly of our own making. A Chemist who should depart from the general com'se, 

 and set himself to prepare substances whose existence is not indicated by theory, 

 would perhaps obtain results of more than the usual interest. 



Among chemical inquiries, if ever such a list as I have ventured to suggest 

 should be drawn out, I hope that many would be included relating to the most 

 familiar substances and the simplest cases of chemical change. The thorough 

 study of a few reactions might perhaps bring in more knowledge of the laws of 

 Chemistry than the preparation of many new substances. 



I believe that if any Chemist not content with a process giving a good yield of 

 some product examines minutely the nature of the reaction, observing its course 

 as well as its final result, he will find much more for study than the chemical 

 equation represents. He will probably also find that the reaction and its con- 

 ditions are of a formidable complexity, and will be driven back towards the 

 beginnings of Chemistry for cases sufficiently simple for profitable study. 



In concluding my remarks, I desire briefly to refer to another branch of Chemical 

 Science, to the advancement of which this Association seeks to contribute — I 

 mean, applied or technical Chemistry. One of the principal differences between 

 the papers read before this Section, as a class, and those which the Chemical 

 Society receives, is the larger proportion in our list of papers on technical subjects. 

 Whatever Chemists may hold, there can be no doubt that the estimation of oiu- 

 science by the outside world rests largely on the well-founded belief that Chemistry 

 is useful. Indeed, though scientific Chemists are justly eager to vindicate the 

 value of investigations remote from any application to the arts, they cannot but 

 feel a livelier sense of triumph when the successful synthesis of a vegetable 

 principle yields at the same time a product of great technical value, as in the case 

 of the production of artificial alizarin. 



By visiting in turn the principal centres of British industry, this Association 

 brings together men engaged on pure and on applied Chemistry. We who come 

 as visitors may hope that om' papers and discussions here may bring fresh 

 interest in the science, if not actual hints for practice, to those whose art or 

 manufacture is based on Chemistry. In return, the most interesting communica- 

 tions the Section has received have not imfrequently been the descriptions of local 

 industries ; and there is no part of our hospitable reception more welcome and 

 more instructive to us than the opportunities which are provided of seeing chemical 

 transformations on a large scale eflected by processes which observation and inven- 

 tiveness have gradually brought to perfection and with the surprising familiaiity 

 and skill which are engendered by daily use. 



* Bull, de la Sec. Chim. de Paris, t. xxiv. p. 114. 



