1879.] On a JVetv Method of Studying Metallic Vapours. 269 



the yellow one, and connected with it by a sap-green vapour. The 

 spectra then visible in the tube at the same time are — 



Leaf-green. . . . Green and red lines of Na and C of hydrogen ; 

 D absent. 



Sap-green Green, red, and yellow Na lines of equal bril- 

 liancy and C of hydrogen. 



Yellow D alone and C. 



Bluish-green . . and F and hydrogen structure. 



To observe the green Na line alone it is necessary to point the direct- 

 vision spectroscope just above the surface of the metal where the 

 green is strongest. It is also necessary to guard against internal 

 reflections from the glass, as this may sometimes cause the D line to- 

 be seen by reflection from the surface. 



The metallic sodium is apt to condense on the surface of the glass 

 and around the platinum pole. If this should happen the retort must 

 be heated until the sodium has again volatilised. The yellow line i& 

 always seen when the coating extends to the pole. 



The following extracts from the laboratory note-book will help to 

 make the method better understood : — 



Experiment with sodium. 



Before heating Na, the following lines were visible in Geissler tube. 



8-8 to 8-9=0. 



9' 72 much brighter than other lines in hydrogen 

 structure. 



10-6 



10'95=Hg green. 

 127 



12-85=F. 

 1385 



15-3 to 15-4 = Hg violet. 

 Colour of spark along tube, pale lilac; its 'spectrum exhibited — 

 Hydrogen structure. 

 C. 



No hydrocarbon spectrum visible. 



Time 11.25. — Na gently heated with spirit-lamp four inches away. 



Almost linear hydrogen spectrum in capillary structure gone or 

 nearly so. 



Hydrocarbon now strong below lower mercury joint. 

 Time 11.35. — Sodium still angular. 

 Hydrocarbon scarcely visible in capillary, 

 is a again warmed. 



11 "7 (hydrocarbon line) increased in narrow tube below lower mer- 

 cury joint, showing that hydrocarbon still comes off. 



