EXPEEIMENTS WITH IONIZED All!. 9 



escapes is now as ineffective as tVoiu a tube with too slow a current or a closed tube. 

 A somewhat similar difficulty is encountered on using; the color tube with a pellicle 

 of phosphoi'us. If this is put too near the jet it will not color it. So an X-ray 

 tube too near the jet is neuti'al. A certain volume for growth of nuclei is appar- 

 ently needed. If the pellicle, figure Ore, is approached through C, figui'e 10, toward 

 the jet or i-enioved from it, blue flashes api)ear between relatively clear fields. In 

 position a, to take another instance, there is pei'maneut coloring due to phosphorus 

 dust slowly entering 6\around the edge. At h, tlie color effect is apt to be absent. 

 The result is unchanged even for a tube, C\ two feet long. Placed in a lateral tubu- 

 lure as at (1), the phosphorus pellicle is ineft'ective, whereas if at (2), (3), or (4), 

 the field is markedly colored. In like manner in using the multiple tulie method 

 for graduation, the place of insertion of the mouths of the tubes of the form AB, 

 figure 9, made a difference in the color effect obtained, caet. par. 



6. — Aspirating air at the rate of several liters per minute over sulphur at 300° 

 did not produce perceptible darkening, although ignited sulphur is very effective. 

 Ignited phosphorus, even when passing oxide visibly into the color tube, is without 

 action. Glass tubes when heated high enough to show the sodium flame on the 

 outside thi-ow an abundance of nuclei into the air current passing through them to 

 the color tube. Other tubes (metallic) are also liable to volatilize sodium vapor 

 under like circumstances, if not quite recently cleaned. In such a case a change of 

 color from yellow to blue through opaque occurs as the tube cools. The phenomenon 

 is complicated by the efllux of hot air. 



7. — For concentrated sulphuric acid, a Wulff's bottle is a convenient apparatus 

 for producing the nuclei, the air being bubbled through it as shown in figure 11. 

 Coal gas as a convection agent is even more effective. Phosphoi'us, P, may also be 

 used in this way, but less efficiently. 



8. — Washing the aii- charged with nuclei has but little effect, if any. Heat, 

 however, seems to exert a tendency to dissociate them. In the apparatus shown, 

 figui-e 11, the nuclei from the Wulft''s bottle were passed through a hot tube, there- 

 after cooled down in a spiral of lead tubing surrounded by crushed ice, then 

 discharged into the color tube O. On examination the hot metallic tube showed a 

 violet-opaque, the cold tube a blue-gray color when the dust was discharged into 

 the color tube, indicating more dust in the first instance. After the removal of the 

 phosphorus fi'om the bottle no color was observed, proving the tube to have been 

 clean at the given temperature. The red-hot metallic tube gave a blue color, 

 however. 



9. — Clean hot copper surfaces removed out of the reducing flame darkened the 

 tube instantaneously, while the oxide coats were forming. As I failed to get the 

 same i-esult with iron, it is probable that ions were cariied out of the flame in 

 tempoi-ary combination with the metal. Sodium (oxidizing) is without effect. 



10. — If air is aspirated through ammonium polysulpbide considerable pressure 

 is needed to produce a colored field. It colors markedly \vhile the liquid is evapo- 

 rating from a wet stopper, for instance. Coal gas is itself but slightly charged with 

 nuclei ; if bubbled through the polysulphide, however, the latter becomes intensely 



