TRANSACTIONS OF SECTION B. 575 



sions of facts of ' position' isomerism, sucli as those pertaining tfi other non-saturated 

 compounds, but more complex to unravel and more varied and interesting. It is 

 doubtful whether the K^kule ring does not remain as efficient a symbol as any 

 stereographic substitute yet proposed for it ; but it itself is purely a symbol of 

 chemical interactions, and has no spatial significance other than what may be put 

 into it by convention. 'Adjacent,' ' opposite,' and the like have only application 

 literally to the arrangement of the symbols ; but if the symbolisation is perfect 

 the ' opposite ' carbons will, as a matter of course, always indicate the same point 

 concerning the chemical interactions. 



Whether the chemical formulje for the lactic acids are better arranged in a 

 plane or as a tetrahedron is to be decided by the facts concerning these and other 

 asymmetric carbon compounds, the object being to syrabohse or formulate as 

 distinct and complementary in certain physical properties, but alike in their 

 chemical interactions, two isomeric substances, simultaneously formed in molecular 

 quantities. Enantiomorphous arrangements of the respective formulae of dextro- 

 and Isevo-lactic acids fully meet the case, but the facts are in no way explained by 

 these formulae. In the enantiomorphously related hemihedral crystals of the cor- 

 responding salts of the dextro- and Isevo-acids, and in their opposite rotatory effect in 

 solution upon the plane of polarised light, we recognise something like a torsioned 

 state of the whole homogeneous substance, something to be accounted for by pecu- 

 liarity of chemical origin, but not something made more intelligible by any imagined 

 arrangement of unlike parts. It is possible to give an account of the chemical 

 facts without making reference to mechanical structure, and then to reason about 

 them somewhat in the following way : Given the case of a substance doubly 

 equipped with the power to take part in a certain interaction, and considering 

 that the exercise of the power can only be single, and tbat it cannot be made 

 without affecting and transforming, or perhaps nullifying, the second equipment 

 with power, predict what will happen. That is the prediction called for con- 

 cerning any interaction which generates an asymmetric carbon compound. The 

 result could never have been predicted ; yet how natural and beautiful it is when 

 it comes to us through experiment enlightened by the genius of Pasteur, Le Bel, 

 and Van 't Tloff ! That answer is that a twinned substance results, one indeed iu 

 most respects and chemically, but tAvo in certain physical properties, characterised 

 by presenting phenomena as of equal and opposite strains, a polarised pair of sub- 

 stances, in fact. What I mean by the double equipment with power is, of course, 

 the pair of identically related and self-identical radicals, or the bivalency of one 

 radical wholly and directly associated with the carbon radical. The case of the 

 oxygen radical of aldehyde is that of the bivalent radical ; the other case is that 

 of the two carboxyl radicals of hydroxytartronic acid, or that of the two methy- 

 lene hydrogen radicals of alcohol which these carboxyls have replaced. The 

 tetrahedral formula with its reflected form admirably symbolises the case of 

 enantiomorphously related pairs of substances. But no light whatever is thrown 

 upon the nature of this pairing by the tetrahedron model ; its value depends upon 

 the fact that as a symbol it so fully matches the constitution of the substances. 



Here I bring my summary of chemical theory and its formulation without 

 hypothesis to a conclusion, hoping that, to some extent, I may have impressed you 

 with the fact that the exposition of even advanced chemistry, in its symbolic, 

 equally as in its ordinary language and nomenclature, is independent of any 

 hypothesis as to the mechanically and chemically differentiated structure of sub- 

 stances, and that chemistry can be studied and still furthur developed without 

 reference to such a structure. I have asked for few or no reforms in the use of 

 either terms or symbols, my point having been only to press for a consideration 

 and discussion of the doctrines of chemistry and the great atomic theory itself as 

 Momething concerned exclusively with experimental chemical facts. 



