48 PRESIDENTIAL ADDRESS — SECTION B. 



elements contained in the compound. All chemical properties are 

 thus referred to the properties of the 92 chemical elements, with 

 the addition of specia'l phenomena solely connected with the 

 arrangement of elements among one another. 



The second step is the Periodic Law of the elements, whereby 

 the 92 elements are shown to have only about 10 different kinds 

 of valency amongst them. The model atom was invented to 

 explain this. It consists of a hollow sphere containing a minute 

 heavy kernel* with a distant ring or shell of electrons, each of 

 which gives a valency; the shell may consist of any number of 

 electrons between 1 and 10, the number and arrangement thus 

 explaining all the possible kinds of valency, and therefore all the 

 strictly chemical properties. 



The third step consists in showing that the remaining 

 (non-chemical) properties of the atom, such as weight, depend on 

 the nature of the atom-nucleus. The nucleus of certain familiar 

 chemical elements has recently been broken down by artificial 

 means, thus showing that the atom is not the indivisible minute 

 sphere that it was supposed to be in the 19th century, but is itself 

 a compound of smaller bodies m a special arrangement. Nitrogen, 

 for example, is shown to consist of 4 particles of weight 3 along 

 with two hydrogen atoms, each being characteristically charged 

 with positive electricity and the whole being held together by 

 "binding negative electrons" to give mass 14 and charge 5. The 

 particle of mass 3 itself is also almost certainly a combination of 

 3 hydrogens and an electron. Chemistry and Physics therefore 

 now depend on two substances only, instead of, as before, on the 

 92 elements of the Chemist. 



The fundamental conceptions of the new atomic theory are 

 those connected with hydrogen in its three forms, viz. : 

 (1) hydrogen-ion (hydrion), the cause of acidity, (2) nascent 

 hydrogen, and (3) free hydrogen gas. 



A. Hydrion is the fundamental and only weight-substance: 

 it consists of unit weight accompanied by unit positive electricity 

 ( = 1 + ), and all the elements, following Prout's hypothesis of 100 

 years ago, are associations of hydrion with electrons ( = 0~) in 

 different numbers and arrangements. The function of the inner- 

 most electrons is to hold the hydrions together, and this the 

 electrons can do even if they are less in number than the hydrions. 

 This combination of a number of hydrions with a smaller number 

 of electrons constitutes an atomic nucleus, which thus possesses a 

 positive electric charge equal to the difference between the numbers 

 of hydrions and electrons present. Thus the nucleus of the element 

 lithium is conceived to consist of seven hydrions held together by 

 four electrons, and this nucleus therefore behaves as possessing 7 

 units of weightj and 3 positive charges. It is to be noted that the 

 size of the hydrion is somewhat smaller than that of the electron, 

 the diameter of which is 4 x 10~ 13 cm. 



* The difference between kernel and nucleus is denned later on. 



+ The electron (or unit negative electric charge) is assumed to be weightless: it is in fact 

 __L of hydrion. 



