XX.] THEORY OF TYPES IN CHEMISTRY. 465 



I endeavored still further to show that hydrogen is to be 

 looked upon as the fundamental type, from which the water- 

 type is derived by the replacement of an atom of H by the 

 residue H0 2 . (American Journal of Science, VIII. 93.) In 

 the same way I regarded ammonia as water in which the resi- 

 due NH replaced 2 . 



I have always protested against the view which regards the 

 so-called rational formulas as expressing in any way the real 

 structure of the bodies which are thus represented. These 

 formulas are invented to explain a certain class of reactions, 

 and we may construct from other points of view other rational 

 formulas which are equally admissible. As I have elsewhere 

 said, "the various hypotheses of copulates and radicles are 

 based upon the notion of dualism, which has no other founda- 

 tion than the observed order of generation, and can have no 

 place in a theory of the science." All chemical changes are 

 reducible to union (identification) and division (differentiation). 

 When in these changes only one species is concerned, we des- 

 ignate the process as metamorphosis, which is either by con- 

 densation or by expansion (homogeneous differentiation). In 

 metagenesis, on the contrary, unlike species may unite, and by 

 a subsequent heterogeneous differentiation give rise to new 

 species, constituting what is called double decomposition, the 

 results of which, differently interpreted, have given origin to 

 the hypothesis of radicles and the notion of substitution by 

 residues, to express the relations between the parent bodies and 

 their progeny. The chemical history of bodies is then a record 

 of their changes ; it is in fact their genealogy, and in making 



independent of the presence of ammonia, and to require only the elements 

 of air and water. (Comptes Rendus, LXI. 135.) Some experiments now in 

 progress lead me to conclude that the appearance of a nitrite in the various 

 processes for ozone is due to the power of nascent oxygen to destroy by oxi- 

 dation the ammonia generated by the action of water on nitrogen, the nitrous 

 nitryl ; so that the odor and many of the reactions assigned to ozone or 

 nascent oxygen are really due to the nitrous acid which is set free when the 

 former encounters nitrogen and moisture. On the other hand, nascent hydro- 

 gen, which readily reduces nitrates and nitrites to ammonia, by destroying the 

 regenerated nitrite of the nitryl, produces ammonia in many cases from at- 

 mospheric nitrogen. [See Appendix, page 470.] 



20* DD 



