As to compounds with triple bonds in their molecules (see CARBON COMPOUNDS), the verdict of stereo-chemistry is that no more isomers are possible than can la• foreseen by the doctrine of atomic linking. This, too, may he best demon strated by means of models.
Hiswin% in conclusion it may be mentioned that the optical rotary power of a substance in the non-crystalline state (sugar in solution) was first observed by Blot in 1815. The optically isomeric tartaric acids were thoroughly investigated by Pasteur, who in 1860 discovered the three known methods of separating such isomers (see above). Ten years later Wisheenus studied the isomeric lactic acids, and in a memoir published in 1871 expressed the view that the doctrine of atomic linking was no longer sufficient for the purposes of organic chemistry. Wislicenus's remark at tracted the attention of Van 't Hoff, who ad vanced the stereo-chemical theory of optical isomerism in 1874. Meanwhile Le Bel, in Paris, had undertaken to continue the work of Pasteur, and soon independently arrived at the same con clusions as Van 't Hoff. Remarkably enough, Le
Bel's and Van 't Hoff's memoirs appeared within one month. The theory of geometrical isomerism was worked out by Van 't Hoff about 1878. At present stereo-chemistry forms quite an exten sive science, and its theories, to which no ex ception has yet been found in the case of carbon compounds, are being gradually extended also to the compounds of nitrogen.
Consult: Wislicenus, (Aber die -riiumliche An ordnung der Atonic, etc. (Leipzig, 1887) ; Hantzsch. Grundriss der Stercoehcnsie (Breslau, 1893; French trans., Paris, 1896) ; Van 't Hoff, Die Lagerung dcr Atonic tilt Rennie (Bruns wick, 1894) ; Bischoff, Handbuch der Stcrrothe iiie (Frankfort-am-Main, 1893). Consult also the works on theoretical and organic chemistry recommended in the article CHEMISTRY. See CHEMISTRY; CARBON COMPOUNDS; LACTIC ACID; TARTARIC ACID; FUMARIC AND MALEIC ACIDS; VALENCY.