3t>6 THE CHEMICAL PROBLEMS OK TO-l^AY. 



The researches iu this direction are so mimerous and so toilsome, and 

 yet tiie result is so surprisiu<;ly simi)le ! The carbou atom is endowed 

 with four, the oxygen atom with two, the hydro;;en atom witii one point 

 of attack for the chemical affinity. The cause of the aggregation of the 

 atoms within the molecule lies iu the mutual saturation of these uuits 

 of atlinity or valen(;ies. It is the number of valencies Mhich decides 

 the possibility of the existence of a compound. Amongst the legion of 

 imaginable combinations of these three elements only those are capable 

 of existence in which every valency is satnrated by that of another 

 atom. Through this knowledge a new method of iiHjuiry was opened, 

 in particular (or organic chemistry, the immense territory of which for 

 many years seemed totally to absorb the working i)ower of chemists. 

 But then dawned the tirst signs of a further development. Hardly a 

 decade had elapsed since the general admission of the doctrine of va- 

 lency when a fundamental deepening of the same was announced, which 

 our science owes to two savants, working independently of each other — 

 to Le Bel and van't Uoff. These chemists, considi ring those substances 

 which turn the plane of polarization ( f light, arrived at views which 

 soon led to a result until then thought to be out of reach, a conception 

 of the aggregation of the atoms within the molecules in space. Thus^ 

 a field of study was created which van't Hoff called "/a chimie (Jans 

 Vespace^' and which we now call Stereochemistry. 



It was recognized that the carbon atom stretched out its four valen- 

 cies in definite directions, and this in a symmetrical manner. The 

 combination of a carbon atom with four other atoms, for example, 

 methane, OH4, is representable by the picture of a tetrahedron in the 

 stereometric center of which the carbon atom is situated, Avhile the 

 hydrctgen atoms occupy its four corners. 



Numerous cases of isomerism, until then not understood, could be 

 explained in this manner and were regarded as stereo-chemical ones. 

 The cause of optical activity was found to consist iu the presence of au 

 asymmetric carbon atom, that is, one which is combined with four dif- 

 ferent groui)s. 



Also the stereometric forms of a few simple molecules were consid- 

 ered; it was recognized, e. r/., that a comi)ound of three carbon atoms 

 linked together by one bond respectively could not contain those atoms 

 in a straight line, but that they must lie in the angles of a triangle the 

 sides of which form au angle ecpial to that in which the directions of 

 valency of the carbon atom intersect each other. 



By the a])plicatioiis of these considerations to more complicated 

 molecules, which contain a (;liain of atoms closed within itself, Adoli)h 

 von Baeyer has enlarged our theory in a manner full of consequence. 



Kekule in times past had recognized that carbon shows a particular 

 disposition to form closed chains of six atoms. The discoveries of Bae- 

 yer and his followers, as well as Fittig's work on lactones, taught that 

 such closed chains or rings formed of fewer atoms also exist. But 



