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XLV. Chemical and Electrical Changes induced by Ultra- 

 violet Light. By Sir William Ramsay, K.C.B., F.R.S., 

 and J. F. Spencer, M.Sc, Ph.D.* 

 [Plates VI. & VII.] 

 Theoretical Introduction. 



IN order to interpret the experiments o£ which an account 

 will be given in the following pages, some hypotheses 

 are necessary. The now almost universally acknowledged 

 theory of corpuscles or electrons mnstof necessity be adopted. 

 It is, however, immaterial, so far as the present work is con- 

 sidered, whether or no it be assumed that what is commonly 

 termed "matter" consists wholly of congeries of electrons. 

 It will prove sufficient for the purpose if the existence of 

 atoms of " matter " be postulated to which electrons have the 

 power of attaching themselves, or of entering into combina- 

 tion. This suggestion was first made by Nernst, we believe, 

 in a lecture delivered before the Grottingen Academy. A 

 positive ion, according to Nernst, may be conceived as an 

 atom of an element which has lost one or more electrons, 

 according to its valency ; a negative ion, as an atom which 

 has gained one or more electrons. Thus Ag* (where * means 

 a + charge) is an ion of silver, i. e., an atom of silver from 

 which an electron has escaped ; and CI' (where ' denotes a 

 — charge) as an atom of a " stuff " which we may term 

 chlorine, but which becomes a chlorion by combining with 

 an electron. The equation AgN0 3 Aq + Xa01Aq = AgCT + 

 NaN0 3 Aq may be written thus, where Q^) signifies an elec- 

 tron :— AgAq -r-NO 3 0Aq + NaAq-f-ClQAq = AgCl + Na A q 

 + NQ 3 0Aq. But it will here be noticed that AgCl is 

 written as if electrically neutral. What has become of the 

 electron attached to the chlorine ? Is it not associated with 

 the AgCl molecules ? When metallic sodium and gaseous 

 chlorine combine to form sodium chloride, the distinctive 

 properties of each element disappear. It is of course open 

 to say that much energy has been lost. True ; but that is 

 no " explanation''' of the change of character of both elements: 

 it is merely a concomitant; no doubt of the greatest im- 

 portance, but unless we endow "energy" with a personality, 

 a quasi-substantiality, and regard what we term " sodium " 

 and " chlorine " as compounds of energy with " chlorine- 

 stuff " and "sodium-stuff''' (which is undoubtedly true in a 

 sense) we fail to secure an " explanation." For the word 

 explanation involves a mental picture in mechanical terms ; 

 * Communicated bv the Authors. 



