BASQUIN. — THE ARC SPECTRUM OP HYDROGEN. 169 



shunted about the induction coil. The deposit iu the hood enclosing 

 the magnesium arc in hydrogen is quite plentiful, has a dark slate 

 color, decomposes water at ordinary temperature, giving alkaline reaction, 

 and oxidizes rapidly on heated platinum. 



Zinc. 



The zinc arc in hydrogen gives a collection of lines between 4300 and 

 4050, having an average intensity from 2 to 4, and not found in the arc 

 in air. This appears to be a set of flutiugs of complicated structure 

 having heads less distinctly marked than usual and running toward the 

 shorter wave lengths. The semi-opaque deposit formed in the atmos- 

 phere of the hood is so considerable that a current of not more than 

 about four amperes can be used. This deposit is dark brown in color, 

 gives alkaline reaction in water, but does not decompose it enough to 

 form bubbles even when heated. It dissolves completely in sulphuric 

 acid, forming a clear solution, and rapidly oxidizes on heated platinum. 



Sodium. 



The sodium spectrum was obtained by using metallic sodium as the 

 cooler rotating electrode and copper as the stationary one. As above 

 mentioned, there is not the slightest trace of any of the hydrogen lines to 

 be detected in this spectrum either visually or on the photographs, but 

 there is a strong series of lines between 5000 and 3800, resembling the 

 hydrogen-magnesium series in character. This is probably a complicated 

 fluting of heads less clearly marked than usual and running toward the 

 shorter wave lengths. A compound of sodium and hydrogen is already 

 well known. The formation of the semi-opaque deposit in the atmos- 

 phere of the hood is so considerable that the arc can be run only about 

 five minutes at a time. I have not tried the sodium arc in air. 



The sodium spectrum obtained in hydrogen is itself quite interesting. 

 All the sodium lines given by Kayser and Runge* come out very clearly, 

 but the principal interest centres about the D lines, which are very in- 

 tense, and so wide as to cover all the region between them. "When 

 observed visually their reversals change in width quite rapidly. At first 

 these reversals may be quite narrow black lines, and then they quickly 

 widen and blot out the whole of the bright field between them. The 

 width of the two lines taken together is about 150 Angstrom units, 

 though the photographic plates are stained for a much greater width. 



* Kayser & Runge, Weld. Ann., 41, 302 (1890). 



