TRANSACTIONS OF SECTION B. 



663 



,MrV(M', we .shall do Av.'ll in this, as iiulurd in all Muiilar casos in science, li nnncni- 

 l)er till' ilaii;j:or pointed out in Itacon's aphorism, that ' The mind di.'lifrhts in spriiiLr- 

 iw^ n)) to the most f;-eiieiiil axioms, thai it may lind rest, bnt after a short slay here 

 it disdains experience,' and to hear in mind tlint it is only tiio law t'nl luiiun of 

 hviiothesis withexperiment which will ])rove a Iruitlid oni: in the ostaldislmient of 

 a'svsti'malic inorji-anic chemistry wliich need not fear comparison with the ordc^r 

 which reiuns in the or^'anic liranch of our science. And lu'ri; it is well to bo 

 reminded that complexity of constitution is not the solo ])rero^ative of the carhon 

 (•(inijiounds, and that Lefore tliis systematisatiou of inorganic, chemistry can ho 

 cUccted we slu'ill have to coni(^ to terms with many conqtounds concerning whose 

 ri>iistitution we are at present wholly in ignorance. As instances of such I would 

 ivl'er to the lini'ly crystalline ])hospho-molyl)dates, containing several hundred atoms 

 ill the molecule, lately ]ireparod by Wolcott (.iihbs. 



Arising out of Kekule's theory of the tetrad nature of the carbon atom, came 

 lliP questions which have caused much de1)ate iunong chemists : (1) Are the four 

 cnnibining units of the carbon atom ol' (squal \alue or not !-^ and ('2) Is the assump- 

 lioii cf a dyad carbiiii atom in the so-called non-saturated c(im])nunds justiji.-iblo 

 (ir not h The answer to the lirst of these, a favourite view of Kolbo's, i^ given 

 in the now Avell-ascertained laws of isomerism; and from the year 186l', when 

 Sclioileninier proved the identity of tho hydrides of the .alcohol radicals with the so- 

 called radicals themselves, this question nniy be saiil to lie set at rest; tor Lesson 

 liiniself aihnils that the existence of hi-< singular isomeric hydroxylamiiu^ deri- 

 vatives can be explained otherwise than liy the assumption of a dillerence between 

 each of the conib'ining units of nitrogen, and the dili'erences supposed by Schreiner 

 to hold good between the niethyletliyl carbonic ethers have been shown to have 

 no existence in fact, ^^'ith respect to the second point the reply is no less dofinite, 

 and is recorded in the fact, amongst others, thatethxlene chloriiydrin yield > on 

 oxidation chhn'acetic aciil, a react ion which cannot be explained on the hypothesis 

 of the existence in ethylene of a dyad carlxin atom. 



Passing from this subject, we arrive, by a ])rocess of natural selection, at more 

 complicated cases of chemical orientation — that is, given certain compounds which 

 jiossess the same composition and molecular fornnda' liut ^■arying properties, to 

 lind the diirerence in molecular struct tn-e by which such variation of pro])orties ig 

 distermined. Problems of this nature can now ))e satisfactorily solved, the number 

 of possible isomers foretold, and this prediction conlirmed by experiment. The 

 general method adopted in such an experimental inquiry into the molecular 

 arrangement or chemical constitution of a given conijiound is either to linild up the 

 structure from less complicated ones of hiunvii constitution, or to resrdve it into 

 such component parts. 'J'luis, for exampl(>, if we wish to discriminate between 

 several isomeric alcohols, distinguishing the ordinary or primary class from the 

 .S('Condary or tertiary class, the existenct^ of whicli was predicted by Kolhe in 

 ISGL*, and of whiidi the first niemlier was prepared by I'Viedel in 1804, we have 

 to study their products of oxidation. If one yields an acid having tho same 

 number of carbon atoms as tho alcohol, it belongs to t lie first class and ])ossesse.s 

 a definite molecular structuri^; if it splits up into two distinct carbon compounds, 

 it is a secondary alcohol ; and if threti carbon compounds result from its oxida- 

 tion, it mu.st be classed in the third category, and to it belongs a definite molecular 

 structure, different from that of the other two. 



In a similar way orientation in tho much more complicated aromatic hydro- 

 carbons can 1)0 eflected, This clas.s of bodies forms the nucleus of an enormous 

 lumiber of carbon compounds which, both from a theoretical and a practical point 

 of view, are of the highest interest. For these bodies exhibit (diaracters and 

 possess a constitution totally different from tho.so of the -so-called fatty .substances, 

 the carbons atoms being linked together more intimat(dy than is the case in the, 

 latter-named group of bodies. Amongst them are found all the artificial colouring 

 matters, and some of the most valuable pharnniceutical and therapeutical agents. 



The discovery of the aniline cidours by Perkin, their elaboration ])y Ilofmann, 

 the synthesis of alizarin by Graebe and Liebermann, being the first vegetable 

 colouring matter which has been artificially obtained, the artificial production of 



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