UNDISCOVERED SUBSTANCES. 79 



has been accomplished by Ladenburg. It seems further probable that 

 at no distant date the useful alkaloids, such as quinine, may also be 

 synthesised, inasmuch as quinoline, one of the products of the decom- 

 position of quinine, and of some of the allied bases, has recently been 

 prepared by Skraup by a method which admits of its being obtained 

 in any quantity. 



Much also has been done in the way of building up compounds 

 the existence of which was predicted by theory. Indeed, the extent 

 to which hitherto undiscovered substances can be predicated is 

 doubtless the greatest triumph achieved by chemists during the past 

 fifty years. 



As yet, however, only the statical side of chemistry has been de- 

 veloped. Whilst the physicist has been engaged in tracing, for the 

 gaseous condition at least, the paths of the molecules and calculating 

 their velocities, the chemist, whose business is with the atoms within 

 the molecule, can point to no such scientific conquests. All that he 

 knows concerning the intramolecular atoms, and all that he expresses 

 in his constitutional formulae is, the particular relation of union in 

 which each of these atoms stands to the others which of them are 

 directly united (as he expresses it) to other given atoms, and which of 

 them are in indirect union. Of the relative positions in space occu- 

 pied by these atoms, and of their modes of motion, he is absolutely 

 ignorant. In like manner in a chemical reaction the initial and 

 final conditions of the reacting substances are known, but the 

 intermediate stages the modes of change are for the most part 

 unexplained. 



The feeling that no number, however great, of successfully solved 

 problems of constitutional chemistry (as at present understood), and 

 no number of syntheses, however brilliant, of natural compounds could 

 raise chemistry above the statical stage that the solution of the 

 dynamical problem cannot be arrived at by purely chemical means 

 has led many chemists to approach the subject from the physical side. 

 The results which the physico-chemical methods, as exemplified in the 

 laws already alluded to of Dulong and Petit, Avogadro and Mits- 

 cherlich, have yielded in the past, offer the best guarantee of their 

 success in the future. And the advantages of many of the physical 

 methods are obvious. Every purely chemical examination- whether 

 proximate or ultimate of a compound, presupposes the destruction of 

 the substance under examination : the chemist ' murders to dissect.' 

 But observations on the action of a substance on the rays of light, on 

 the relative volumes occupied by molecular quantities of a substance, 



