M. Pastcui' 0)1 Aspartic and Malic Acids. 289 



reasoning, strengthened by other examples ah'eady known, ap- 

 pears to him to permit the conjecture that many organic sub- 

 stances naturally endowed with the rotatory power may have in 

 the same manner their inactive isomeric equivalents, which che- 

 mists should endeavour to obtain. Thus also, inversely, an 

 organic product obtained artificially can no longer be considered 

 as identical with the natural substance which its composition 

 and even its reactions represent, unless the identity, or at least 

 the equivalence of the crystalline forms, have been established, 

 and above all, the presence of the rotatory power when the sub- 

 stance which is to be reproduced possesses it naturally*. 



Let us for a moment consider these same facts of isomerism 

 in a purely chemical point of view, by deducting all the data which 

 their crystallographicaland optical study have contributed towards 

 their explanation. Let us suppose that the two aspartic and malic 

 acids, togetlier mth their respective salts, had- been occasionally 

 obtained without their distinctive molecular characters having 

 been known. In this case there wou.ld be two series of bodies, the 

 correspondent pairs of which would have shown themselves as 

 identical with each other in composition, reactions, atomic for- 

 mulae, and derivative products. Thus, according to principles, 

 or as we ought rather to say, according to the practice habitually 

 adopted by chemists, these facts would inevitably lead to the 

 confounding of these two classes into one. This was in fact 

 what happened when artificial aspartic acid was originally dis- 

 covered, and it could not have been otherwise. Nevertheless, on 

 examining them more closely, differences are perceived, slight, it 

 is true, but constant and appreciable, in the facility with which 

 the various transformations of the bodies take place, in the time 

 which they take to act, in the temperatures and the quantities 

 of the same solvents which are necessary to produce parallel 

 results. Now these peculiarities, which are ordinarily neglected, 

 are found here to be intimately related to those molecular differ- 

 ences which their existence should have sufficed to point out. It 

 is these differences which we now discover to be in themselves 

 far more important than there has hitherto been occasion to 

 believe, and to which it is necessary in general to devote much 

 more attention than it has been customary to do. The same 

 change is effected in chemistiy by this discovery as was formerly 



* The rotatory power furnishes a stron;^, although not absolute indica- 

 tion of identity when it is found the same in direction, in absolute inten- 

 sity, and the mode of dispersion in equal quantities in parallel solvents 

 taken at the same temperature. The absence of one of these conditions is 

 a positive i)roof of difference. The identification of the crystalline forms 

 may sometimes be rendered uncertain by the accidents of dimorphism. It 

 ii this case of possible ambiguity attached to the cr}stallograpliical charac- 

 ters which we have been desirous of pointing out in our summary. 

 Phil. May. S. 4. Vol. 4. No. 25. Od. 1852. U 



