﻿144 Mr. Clinton J. Davisson : Rule Played by Gases 



emission at not too high a temperature, and one for which 

 the curves should be, at the same time, as free as possible 

 from time variations. These requirements were found to be 

 met most satisfactorily by a sample of aluminium phosphate. 

 The only unfortunate thing about this particular sample was 

 that the large emission seemed not to be characteristic of the 

 salt itself, but to arise from sodium which was present as an 

 impurity. Only after the salt had been heated for hours 

 together did the value of e/m indicate an emission of alu- 

 minium ions, and then only at temperatures in the neigh- 

 bourhood of 1200° C. 



That the larue emission was, in fact, due to sodium w r as 

 made more certain by an examination of the flame spectrum 

 of aluminium phosphate from the same supply. A Grouv 

 sprayer was partly filled with distilled w 7 ater, and the spray 

 from this forced into a Bunsen flame in the usual way. The 

 spectroscope under these circumstances revealed only an 

 occasional faint flash of sodium. On adding a small quantity 

 of the aluminium phosphate to the distilled water the D lines 

 immediately shone forth. 



The first measurable emission from this aluminium phos- 

 phate occurred at about 550° 0. The curves were very good 

 and gave with the other data 254 as the value of e/m. This 

 was taken to indicate potassium, 249. The salt was then 

 heated continuously at this temperature for twenty-one hours. 

 After this heating curves were taken at 600° C. which seemed 

 to indicate sodium, the value of e/m being 439, compared 

 with sodium 421. That the potassium value did not persist 

 in this case, as in the case of the other phosphates tested, does 

 not seem unreasonable. The aluminium phosphate was from 

 a supply furnished by Kahlbaum, while the others were 

 prepared in the laboratory from a common supply of am- 

 monium phosphate. Further determinations of e/m during 

 the next forty hours indicated that the emission was homo- 

 geneous, beautifully regular, and altogether suitable for the 

 proposed tests. 



The gases which have been tested are air, hydrogen, and 

 carbon dioxide. In each case the apparatus was first 

 thoroughly washed out with the gas to be investigated and 

 the pressure then reduced to the lowest attainable. The 

 gases were in all cases carefully dried. A pair of curves was 

 taken at this low pressure. A small quantity of dried gas 

 was admitted to the apparatus. The pressure was recorded 

 and curves again taken. This was repeated until further 

 measurements were impossible. 



The results for these experiments for air are graphicallv 



