December 1, 1894.] 



KNOWLEDGE. 



267 



THE RISE OF ORGANIC CHEMISTRY. 



By Vaughan Cornish, M.Sc, P.C.S. 



ORGANIC chemistry, the study of the hydro-carbons 

 and their derivatives, is a science of the present 

 century. Some of the technical processes con- 

 nected with the preparation of organic substances 

 are, however, of very ancient origin — brewiiig^Jor 

 instance, and the art of soap-making. It is the scientific 

 aspect of the subject with which we are concerned in the 

 present article, and which occupies the greater part of 

 Prof. Smithells' new and enlarged edition of Schorlemmer's 

 "Rise and Development of Organic Chemistry." 



Lavoisier showed that the decomposition of sugar by 

 fermentation proceeds according to the conditions of the 

 law of conservation of mass, the carbonic acid and alcohol 

 produced being equal in weight to the sugar from which 

 they are formed. Early in the present century the 

 Swedish chemist, Berzelius, showed that the composition of 

 organic substances conforms to the laws of constant 

 proportions and of multiple proportions, which Dalton and 

 others had shown to be characteristic of mineral compounds. 

 The way was now paved for the recognition of the study of 

 organic materials as a part of the domain of chemistry con- 

 forming to the same laws as those which govern the chemical 

 properties of mineral substances. Research in the organic 

 branch of chemistry was immensely facilitated by Liebig's 

 work in perfecting the principal process of organic analysis, 

 the well-known " combustion " which is still the pons 

 asinonim of the student's laboratory course. From Liebig's 

 time the progress of organic chemistry has been marvellously 

 rapid. The compounds of carbon are, for the most part, so 

 "reactive" that the labour of the investigator is quickly 

 rewarded by the production of some novel substance — often 

 useful or curious — the discovery of which leads in its turn 

 to the production of other bodies related to, but differing 

 from it. The binding element in the majority of these is 

 carbon. The carbon atoms seem to have an almost 

 unlimited capacity for catching hold of and hanging on to 

 one another, and at the same time they retain their hold 

 upon one or more atoms of other elements with which they 

 have been associated. Thus, in the laboratory of the plant 

 or animal body, and in the laboratory of the chemist, are 

 built up compounds of almost infinite complexity, though 

 containing for the most part but few of the chemical 

 elements. Carbon is present in all, hydrogen in almost 

 all, and oxygen in a majority of cases. Nitrogen occxirs 

 frequently, and the other elements in smaller quantity and 

 comparatively seldom. The known hydro-carbons — i.e., 

 compounds containing only hydrogen and carbon — number 

 four hundred, whilst few of the elements except carbon 

 combine in more than two or three proportions with 

 hydrogen. 



The total number of carbon compounds is said greatly 

 to exceed that of all the other known chemical substances. 

 Among the organic bodies which have been produced in 

 the laboratory are many useful drugs and invaluable 

 anaesthetics ; dyes, of which many are brilliant and some 

 are beautiful ; and powerful explosives, the discovery of 

 which has probably proved beneficial to manufacturers of 

 war material. But in the limits of this article we must 

 not diverge from science to technology. 



The facility with which chemists can transmute one 

 carbon compound into another has led to great develop- 

 ments in our knowledge of the mechanism of chemical 

 reactions, and of the chemical structure of substances. 

 Chemical formulie, from expressing merely the quantitative 

 composition of compounds, were soon used to express 



the methods of formation and decomposition of organic 

 substances. As knowledge advanced it was seen that the 

 formulffi could be made to indicate the way in which the 

 atoms were united one to another. It appeared from the 

 study of organic chemistry that the attraction or union of 

 an atom is not so much with all the rest of the molecule 

 as with some neighbouring atom with which it is closely 

 united or related. The iirnjildc forwuhe, with which modern 

 chemical books are full, express, symbolically, the order or 

 arrangement in which the atoms of the compound molecule 

 are boun(lo^ linked together. To such perfection has 

 the symbolical expc^sion of the constitution of organic 

 substances been brought, that the manipulation of these 

 symbols often furnishes' a valuable guide in the prosecution 

 of new researches. No mode of expressing graphically -m 

 paper the composition of a molecule can, however, be 

 expected to be quite satisfactory if it fails to take account 

 of the fact that the atoms of a molecule are not all 

 distributed, and do not all move, in one plane. The 

 ordinary graphic formula of the text-book has the same 

 faults as, say, the Bayeux tapestry, or a Chinese battle 

 picture — it takes no account of perspective. The more 

 recent use of nhjptic symbols (which look like outlined 

 figures of crystal form), or of actual models, is an im- 

 portant extension of this domain of scientific symbolism. 

 We must explain shortly how these developments have 

 come about. The study of carbon compounds led to 

 the discovery of isomerk bodies which differ in their 

 properties, although their analytical composition is identical. 

 These differences must, it seems, be explained on the 

 supposition of a different grouping of the chemical atoms, 

 and the phenomena of isomerism are to be classed along 

 with those of allotropy, which are exhibited by several 

 elementary substances, notably by carbon itself (vide 

 Knowledge, 1892, "Carbon"). In the case of carbon 

 compounds, it was found possible in many cases to express 

 these differences by the graphic formulte referred to above. 

 Thus, there are two substances of very different properties, 

 the percentage composition of which is expressed by the 

 formula CoHgCU— the symbols C, H, and CI standing for 

 weights of carbon, hydrogen, and chlorine, proportional 

 to the weights of the atoms of these bodies. It was found 

 that in one of the two substances whose composition is 

 expressed as above, both chlorine atoms were bound up to 

 the same carbon atom, whereas in the other the reactions 

 showed that each carbon atom was m intimate connection 

 with only one atom of chlorine. These facts are symbolized 

 as follows : — H H 



1 I 



H— C— H H— C— CI 



I and I 



Ci_C— CI H— C— CI 



But these graphic symbols are insufficient to explain some 

 cases of isomerism. For such cases it is useful, instead 



of using the symbol — C — , to represent the carbon atom 

 by a tetrahedron. [ 



This symbol expresses the essential fact that the 

 carbon atom has a fourfold power of union with other 

 atoms, and we symbolically express the 

 union by attachment to the corners of the 

 figure. It is generally sufficient for the 

 purpose in view if one or two carbon 

 atoms are thus fully represented, the 

 ordinary symbol being employed to show 

 the functions of the other carbon atoms. The two sub- 

 stances, fumaric acid and maleic acid, have the molecular 



