Page:The American Cyclopædia (1879) Volume IV.djvu/378

 370 CHEMISTRY of water and distillation, alcohol is obtained. By analogous processes, any of the hornologues of olefiant gas being substituted for it, the cor- responding alcohols may be prepared. More than half a century ago Chevreul by a classical research proved that the fats are composed of various acids united with a peculiar sweet base, called glycerine. Subseqnently Berthelot suc- ceeded not only in recombining the fat acids with glycerine, thus forming the original fats, but also caused all the more common mineral and organic acids to unite with glycerine in a manner precisely analogous. Moreover, by substituting for glycerine any of the various species of sugar, similar combinations have been obtained with the fatty and other acids. The indefinite extension which has thus been given to the chemical idea of the fats is a good example of the spirit of generalization now greatly in vogue. The comparatively im- mense development which the study of organic compounds has taken of late years has at length brought chemical science to such a position that a new epoch seems not remote. The laws by which the chemical relations of inorganic compounds have hitherto been so well explain- ed, fail in many cases when applied to organic Bubstanc.es. The domain of organic chemistry has become so vast that it will soon assert its right to control the whole science. Several chemists have called attention to the apparent necessity of such reformation. It is acknowl- edged on all sides that the artificial division of chemistry into organic and inorganic, which has been admitted for some years, is entirely arbitrary, and in many respects unfortunate. That the science shall once more be consolida- ted is earnestly desired. The doctrine of sub- stitution has already cleared up many matters in inorganic chemistry which had hitherto been inexplicable ; while the question of doubling the equivalent weights of several of the ele- ments in order to bring them into accordance with their combining volumes and certain other of their properties is still open. The extraor- dinary analogy between homologous groups of organic compounds and certain small groups of the elements, as chlorine, bromine, and iodine, has been remarked by several chemists. It has been generalized by Prof. J. P. Cooke of Cam- bridge, Mass., who has shown that not only isolated triads, but all the elements, may be brought into such homologous series, expressed like those of organic compounds by the general formula a + rib. The properties of the members of these series vary in degree in a regular man- ner according to their position, as in the se- ries of organic bodies. Dumas criticised and in a measure modified Cooke's classification, while acknowledging its merit. The bear- ing of tliis subject upon the relations of compound radicals to the so-called elements cannot fail to strike every obsen-er; the dif- ference between them consisting > : mply in the ability of chemists to separate the "former into several ingredients, while the latter are ele- mentary only because they cannot as yet be thus decomposed. Without occupying thorn- selves with the investigation of a problem, the transmutation of metals, to the solution of which their science in its present condition of- fers no clue, chemists have ceased to ridicule the aspirations of the alc-hemists, although they will always condemn the venal spirit which actuated them. The possibility of effecting such transmutation has of late, however, been more strongly suggested by the discov- ery of several remarkable examples of allo- tropism, a term employed to signify that the same body may exist under two or more different conditions, possessing distinct phys- ical and chemical properties. The fact that bodies so entirely unlike in their properties as the diamond, graphite, and charcoal are, chem- ically speaking, identical, standing as it did for a long time an almost isolated example, excited comparatively little attention. Nor was much notice taken of the different states of sulphur, and of other bodies the allotro- pism of which was less clearly apparent. But a deep interest was awakened by the discovery of ozone (allotropic oxygen) by Schonbein of Basel, and especially of red phosphorus by Schrotter of Vienna, bodies as unlike ordinary oxygen and phosphorus as can be conceived in every respect but their combining equivalents and reconvertibility into each other. The ob- servation that the elements boron find silicon are, like carbon, susceptible of three modifica- tions, strengthened this feeling. These dis- coveries recalled attention to the fact that sev- eral of the metallic elements have identical equivalent weights, as cobalt and nickel, pla- tinum and iridium, &c. ; the question naturally arising whether they may not be allotropic modifications of one and the same substance, especially as such modifications of several sub- stances preserve their peculiarities even when combined in similar quantities with other bodies; for example, the compounds of the red and green varieties of the sesquioxide of chromium. Even the idea attached to the term element has been somewhat modified. At one time it was regarded as expressing not only a certain relative weight of a simple substance, but this substance was supposed to possess constant properties, which were as indestructiMe as the element itself. In- stead of this view, which is at present unten- able, the old idea of essence lias been in a measure restored. It would be of course im- possible to enumerate here all the valuable labors which have recently been performed by chemists. Those of II. Rose (1795-1864) in developing inorganic analysis ; of Regnault, Bunsen, Kopp, and Magnus (1802-"TO) in in- vestigating the physical laws connected with chemistry, and of the first two of these chem- ists in perfecting the processes of gas analysis ; of Rammelsberg, Pasteur, Pelouze, Redtenba- cher, Malaguti, Williamson, Heintz, Rochleder, Stadeler, Strecker, Cahours, Anderson, Kolbe,