236 Mr. J. F. Heyes on the 



dyad might unite not only with two atoms of a monad, but 

 also with four atoms of a monad, the four at.oms of the monad 

 splitting into two groups each/' He says : " Regarding 

 oxygen, then, as a dyad, the molecule of water consists of 

 three primaries H 2 — — 0/' I do not know the exact signi- 

 ficance of his marks, but the analogous formula now pro- 

 posed is H 2 = 0=0, or at least H 2 =0==0. It is at least 



0— H 

 preferable to the symmetrical I in better exhibiting its 



reactions, and as the modern representative of the late Sir B. 



Brodie's H 2 00, which has the no small merit of distinguish- 

 ing between the two atoms chemically dissimilar. The 

 novelty (so far as I know) of formulating a divalent and a 

 tetravalent atom of the same element in one chemical mole- 

 cule will, I hope, provide fruitful discussion with those 

 chemists who are not prepared to reject or scorn the child- 

 hood of constitutional formulae. 



However hypothetical our constitutional formulae of most 

 inorganic bodies may yet be, I venture to doubt the wisdom 

 of abandoning the use of our valence-marks, linkings, so-called 

 double bonds, &c. in favour even of the single mark proposed 

 some years ago by Lessen. They may still be used with 

 advantage to chemical science, but not usually to those who 

 are beginning its study. The fact is that the one-sided study 

 of inorganic chemistry, with its numerous elements, and there- 

 fore greater delicacy and intricacy of valency-variation, would 

 make us pessimists, and the isolated study of organic che- 

 mistry, with its few elements, would keep us optimists. The 

 reaction of the constitutional school of chemists upon the 

 empirical formulae of inorganic chemistry has been, in some 

 respects, rather premature in its attempts to solve too much 

 at the outset; but the real laws of valency must be substan- 

 tially the same in both. Thus we have the radical or group- 

 ing — the organic atom so to speak — of ethyl (C 2 H 5 ) always 

 of one valency, but (C 3 H 5 ) is both mono- and tri-valent. Nay, 

 more. What would be called the allotropic modifications of 

 this "atom" — were it an atom — are well known, and can be 

 separably recognized. If (C 3 H 5 ) were an elementary atom, it 

 would be called usually trivalent but occasionally univalid ; 

 or, if no distinction is to be made, trivalent and monovalent 

 after the fashion of gold or thallium. There are not less than 

 five trivalent (C 3 H 5 ) '" ; and their compounds with either 

 chlorine, oxygen, or hydroxy 1 are all known. 



