A HALF-CENTURY OF SCIENCE. 213 



and indigo. The problem of the natural alkaloids has also been at- 

 tacked, in some cases with more than partial success. Methylconine, 

 which occurs along with coninc in the hemlock, has been recently pre- 

 pared artificially by Michael and Gundelach, this being the first in- 

 stance of the synthesis of a natural alkaloid. A proximate synthesis 

 of atropine, the alkaloid of the deadly nightshade, has been accom- 

 plished by Ladenburg. It seems further probable that at no distant 

 date the useful alkaloids, such as quinine, may also be synthesized, 

 inasmuch as quinoline, one of the products of the decomposition 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 quan- 

 tity. 



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. While 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 oc- 

 cupied 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. 



Owing to a 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 can not 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 Mitsch- 

 erlich, have yielded in the past, offer the best guarantee of their suc- 

 cess 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, 

 on its velocity of transpiration in the liquid or gaseous state these 



