ENERGETICS 41 



Structural formula; sometimes say too much even when regarded merely as records of 

 experimental results ; in other ways they do not say enough. A. W. Stewart points out 

 (Chemical World, December 1912, p. 415) that in the formula for acetic acid, if written 

 thus : 



CH 3 C=0 



OH 



there is experimental evidence that the three methyl hydrogen atoms are different from the 

 hydroxyl one, but that there is no evidence for the existence of a CO group ; none of the 

 reactions characteristic of its presence are given by acetic acid. In order to make the formula 

 inform us of-the difference between the various hydrogen atoms, which is not diiectly indicated, 

 we have to treat the groups CH 3 and OH as wholes, saying that hydrogen is not the same 

 when united with oxygen as when united with carbon. Moreover, carboxyl, as such, is not 

 present in acetic acid ; when CO is united with OH, a new radical, COOH (carboxyl), is formed, 

 which must itself be taken as a whole, so that the formula of acetic acid is more correctly 

 written : 



CH 3 -COOH. 



These components of organic compounds behave, as it were, as elements, and, strictly speaking, 

 to make structural formula: more complete in certain ways, it would be necessary to give each 

 of these radicals a distinctive symbol. The essence of chemical combination is, of course, that 

 the properties of elements are changed when united with others, as in the common illustration 

 of mercuric iodide. The object of these remarks is merely to advocate more critical use of 

 structural formula; than is apt to be made by a certain school of chemists, who appear to 

 think that, if a formula can be made to indicate the possibility of a particular mode of 

 combination, the fact is in itself proof that such a reaction actually occurs. G. H. Lewes 

 (1864, p. 131) refers to the profound psychological mistake of holding " that whenever man 

 can form clear ideas, not in themselves contradictor}', these ideas must of necessity represent 

 truths of nature." This view was, at one time, very widely held, and even by so great a man 

 as Descartes. For further discussion see Karl Pearson's book (1911, chapter viii.). 



THE CARBON ATOM 



The question may properly be asked, What are the peculiarities that make 

 organic chemistry a special domain and of especial importance in physiological 

 science? The reason lies, as van't Hoff (1881, i. p. 34 ff., and ii. p. 240 ff.) 

 points out, in the characteristic qualities of carbon itself. This author 

 enumerates five items : 



1. The quadri valence renders possible an enormous number of derivatives 

 of any one compound. 



2. The capacity of carbon atoms of uniting with each other allows a great 

 variety of modes of combination. 



3. Its position in the periodic system, in the middle between positive and 

 negative elements, gives it the power of uniting with the most different 

 elements hydrogen, nitrogen, oxygen, chlorine, etc. (see the table in Nernst's 

 book, 1911, p. 180). Owing to this, it is readily capable of alternate oxidation 

 and reduction, and thus of acting as a carrier of energy. 



4. When three of its valencies are saturated, the fourth valency has a 

 "positive" or "negative" character, according to the nature of the groups in 

 the other three places. Thus while 



is usually " negative," 



is markedly "positive," like hydrogen. 



5. The slowness of reaction or inertia of the carbon compounds is of much 

 significance in vital pITenomena. As an illustration, methyl sulphonic acid is much 

 more stable than sulphurous acid, having a methyl group in place of hydrogen. 



EFFECT OF TEMPERATURE ON THE RATE OF REACTIONS 



Chemical reactions arrive at their point of equilibrium and stop dead at it 

 without overshooting. They are, in fact, aperiodic, like processes in general 



