312 BELL SYSTEM TECHNICAL JOURNAL 



when introduced into the discharge-tube, vaporizes fast enough to 

 supply the desired atoms to the discharge but not fast enough to 

 inhibit the current or clog the tube. Curious observations have been 

 made upon the behavior of some of these strange compounds in a 

 current-carrying gas; of osmium tetroxide, for instance, Aston relates 

 that it had upon the discharge an effect to be compared with the 

 injection of a powerful drug into a living organism. 



So much success has attended these efforts that the conquests yet 

 remaining to be made are few, and it is a much quicker affair to list 

 the as-yet-unanalyzed elements than the analyzed. In order of 

 increasing atomic number (which I place in front of each symbol) 

 they are: 43 Ma (a lately-discovered element); 45 Rh, 46 Pd (two 

 members of the second of the "triads"); 61 to 71 inclusive, excepting 

 68 Er (ten rare-earth elements); 72 Hf (likewise lately discovered); 

 77 Ir, 78 Pt (two members of the third triad); 79 Au; and the elements 

 beyond 84, of which all but three (88 Ra, 90 Th, 92 U), being unstable, 

 are very scarce.* Some of these must owe their absence from the list 

 of the conquered to their rarity, but many are common enough, and 

 what is lacking is a way of driving their atoms into the open and 

 ionizing them. 



The other list, that of the analyzed elements, now^ comprises sixty- 

 six. Among these are distributed nearly two hundred kinds of atoms 

 of different masses. I count 198 in one of the tabulations, but of 

 these some twelve or fifteen are marked as somewhat doubtful, because 

 their ostensible lines on the plates are either very dim or else might 

 be ascribed to some other kind of substance. (Thus if two kinds of 

 ions are observed which differ in mass by one unit, it is often possible 

 that the lighter may be an ionized atom and the heavier an ionized 

 molecule of the hydride of that atom, instead of both of them being 

 ionized atoms of unequal masses.) Among the 198 there are several 

 of which the existence was first deduced from band-spectra; some of 

 these have since been detected in mass-spectra, notably the minor 

 isotopes of oxygen, O'^ and O'^ (I adopt the practice of writing atomic 

 mass as a superscript to the chemical symbol) ; others. Be* and C^^ for 

 example, have not yet been confirmed in this manner, but the evidence 

 from the bands is strong. 



These nearly two hundred isotopes do not exhaust the list. There 

 are in addition the radioactive atoms, of which there are known at 

 present thirty-six varieties, distributed over the last twelve places of 



''At the recent Chicago meeting of the A. A. A. S., Aston announced that he had 

 analyzed uranium, finding a single isotope of mass about 238. This does not speak 

 against the extra isotope of mass 234 appearing in Fig. 7, which is inferred from the 

 study of radioactivity and is known to be too scanty to appear on Aston's plate. 



