548 



SCIENCE. 



[N. S. Vol. XII. No. 302, 



newer conceptions of tlie carbon atom to the 

 atoms of other elements also. Whether we 

 shall ever have a stereochemistry of all the 

 elements is very questionable. As I shall 

 point out presently, carbon compounds in 

 general possess a kind of inertia, a tendency 

 to retain their structure, the possibility of 

 isomerism being due to this. At a higher 

 level of temperature, ordinary structural 

 isomers tend to assume the most stable form 

 or system, while those isomers the existence 

 of which depends on asymmetric carbon 

 atoms tend to form a mixture composed of 

 equal portions of both right- and left-handed 

 forms ; both dextro- and Itevo-tartaric acids, 

 for example, giving racemic acid on heating. 

 That we do not find more cases of structural 

 or of steric isomerism among inorganic 

 bodies is perhaps due, not to their existence 

 being inherently impossible, but to our 

 ■vyorking at too high a tempei'ature, a tem- 

 perature at which isomers are incapable of 

 existence, lapsing at once into the most 

 stable forms or into a mixture of structur- 

 ally equivalent but geometrically opposite 

 bodies, which, like the constituents of ra- 

 cemic acid, are identical in chemical and 

 most physical properties, and which, exist- 

 ing in equal quantities, balance each other 

 optically and crystallographically, like the 

 two tartaric acids. The asymmetric tin 

 atom shows great lability at ordinary tem- 

 peratures. At a temperature much below 

 zero, such steric and structural isomers may 

 well exist independently. The investiga- 

 tion of this is but one of the many possibili- 

 ties of low temperature work. 



This brings us to a comparatively new 

 and highly important branch of organic 

 chemistry, the subject of tautomerism, and 

 this, like stereochemistry, is an outgrowth 

 of the subject of isomerism. Van't Hoff, 

 in his remarkable, but little known book, 

 ' Ansichten iiber die organische Chemie,' 

 points out, as one of the reasons for the ex- 

 istence not only of the large number of 



carbon compounds, but also of isomers, the 

 peculiar inertness of the union of carbon 

 with itself and with other elements. Every 

 one knows that in general the reactions of 

 carbon compounds take place slowly, they 

 form with diflQculty and once formed are 

 comparatively stable ; there is a tendency 

 to maintenance of the status quo. In the 

 language of physical chemistry, we may say 

 that carbon compounds usually tend to equi- 

 librium with great slowness. They have 

 a very small reaction velocity. By virtue 

 of this property, the reason for which we do 

 not know, the organic molecule, once 

 formed, tends to maintain its individuality, 

 hence the stability of isomers. Were it not 

 for this, it would rapidly lapse to the sys- 

 tem which is most stable, whether it be 

 another simple body or a mixture. Just 

 the opposite is characteristic of the inor- 

 ganic molecule. We know a few inorganic 

 isomers, it is true, but their occurrence is 

 so rare as to excite comment. We are, for 

 example, acquainted with three organic 

 compounds C^H^NOj, namely, ethyl nitrite 

 C^Hj.ONO, nitroethane C^Hj.ISrOj, and a 

 less stable form of this, CH,.CH=]SrO.OH, 

 but we know but one nitrous acid and one 

 series of metallic nitrites ; we know but 

 one sulphurous acid and one series of its 

 metallic salts, while there are two series of 

 organic derivatives, the sulphurous ethers 

 and the sulphonates ; but one hydrocyanic 

 acid and one series of metallic cyanides, 

 while there are two series of organic deri- 

 vations, the nitriles and isonitriles ; but one 

 sulphocyanic acid with two series of organic 

 derivatives, the sulphocyanates and the 

 mustard oils. Such examples might be 

 quoted indefinitely. Any one who has at- 

 tempted to synthesize complex inorganic 

 bodies by following the methods of organic 

 chemistry must have been struck with the 

 comparative rareness with which the de- 

 sired results are obtained. In general, then, 

 while organic isomers possess considerable 



