October 12, 1900.] 



SCIENCE. 



549 



stability, of the theoretically possible inor- 

 ganic isomers expressed by any formula 

 only one form is stable, and the others, if 

 momentarily formed, tend to lapse spon- 

 taneously into this. As van't Hoif says, 

 the carbon atom tends to confer on the 

 molecule the power of storing up an enor- 

 mous amount of energy, which power, for 

 want of a better name, is termed the inert- 

 ness of the carbon combination. It is this 

 property, perhaps more than any other one 

 fact, which distinguishes organic from in- 

 organic compounds. 



All organic isomers do not possess this 

 power of maintaining their individuality to 

 the same extent. We find every degree of 

 transition from the stable to the labile, 

 from those isomers which are not intercon- 

 vertible at any temperature short of total 

 decomposition, to those which change into 

 each other upon the slightest provocation, 

 such as slight elevation of temperature, 

 fusion or solution, the presence of catalj'zers 

 or of bodies capable of reacting only with 

 one form ; from those whose individuality 

 and stability are marked, to those where one 

 form is stable, the other labile, and where 

 the lability may vary to such an extent 

 that in some cases the unstable form is 

 easily obtained, in others only with the 

 greatest difficulty, while in still others it is 

 too unstable to exist at all under attainable 

 conditions, and the isomerism disappears. 

 It is the study of labile isomerism which, 

 under the name of tautomerism, has attained 

 such prominence in recent years. In the 

 phenomena of labile isomerism, organic 

 chemistry shows a distinct approximation 

 to inorganic chemistry ; the characteristic 

 phenomena underlying tautomeric organic 

 bodies and inorganic bodies is the same, 

 namely, the tendency to pass easilj' from a 

 labile to a stable form, in short, the ab- 

 sence, more or less marked, of the property 

 which van't Hoff called inertness of union. 



An extreme case of lability in one isomer 



is found in that of the hypothetical vinyl 

 alcohol, CH^ = CHOH. Keactions which 

 theoretically should give this, in reality 

 yield aldehyde, CH3.CHO ; the stability of 

 the former is so slight that it passes at 

 once, if formed, into the isomeric aldehyde. 

 Baeyer obtained two ethyl-isatines, to which 

 should correspond two isatines, while in 

 reality but one exists. Allied to this is the 

 behavior of phloroglucine, symmetrical tri- 

 oxy-benzene, which, with acetyl chloride 

 gives an acetate, indicating that its form- 

 ula is 



OH 

 C 



/^ 

 HC CH 



II I 

 HOC COH 



\^ 

 C 

 H 



while with hydroxylamine it yields an 

 oxime, which is explicable only on the as- 

 sumption that it has the constitution 



O 



C 



/\ 



H,C CH, 



I I 

 OC CO 



It is, therefore, impossible, by using the 

 usual reactions for phenols and ketones, to 

 ascertain to which of these groups phloro- 

 glucine belongs. Baeyer held that but one 

 of the forms actually exists in the free 

 state, the other, the pseudo-form, as he 

 termed it, being too unstable for existence. 

 Laar, on the contrary, held that in such 

 cases both formulas are equally justifiable; 

 that each molecule is constantly shifting 

 back and forth between the two forms, each 

 having but a momentary existence, and to 

 such bodies he applied the term tautomeric. 



The discussion on the nature of tauto- 



