CHAPTER I. 



EMISSION SPECTRA OF METALS IN HYDROGEN. 



In Carnegie Publication No. 35 the writer presented the results of an 

 examination of the arc spectra of various metals. It was there shown that 

 only the alkali metals have strong emission lines in the infra-red. In the 

 case of metals like copper, iron, and zinc there was a weak continuous 

 spectrum in the region of 2 to 3 fi, which appeared to be due to the hot 

 oxides formed in the arc. If this be true, then one would expect to elimi- 

 nate this radiation by producing the arc in an atmosphere of hydrogen. 

 During the past year (1907) this work has been repeated, using an arc 

 inclosed in a metal case which was filled with hydrogen. A Rubens 

 thermopile was used to measure the radiation. The galvanometer had a 

 full period of 16 seconds; its sensitiveness was i=i.7Xio -10 for a scale at 



1 m. When used with the thermopile the temperature sensitiveness was 

 such that a deflection of 1 mm. = iXio~ 5 C. for a scale at 1 m. 



The spectrum was produced by means of the rock-salt prism and mir- 

 ror spectrometer (slits 0.5 mm.) which were described in Carnegie Publica- 

 tion No. 65. 



(a) NICKEL ARC IN HYDROGEN. 



With this outfit the emission spectrum of nickel in hydrogen was exam- 

 ined. The window of the metal case inclosing 

 the arc was of thin glass which absorbed all the 

 radiation beyond 3.5 ll. The metal electrodes 

 were about 1 cm. diameter, with the ends cut 

 wedge-shaped. This produced a long narrow 

 arc, an end-on image of which was projected 

 upon the spectrometer slit by means of a 12 cm. 

 focus, concave mirror. 



The spectrum appeared continuous in the 

 red, where the maximum radiation was observed. 

 The results are shown in fig. 47, where a strong 

 emission is to be observed at 0.75 y.. Beyond 



2 ll the radiation from the hot electrodes is indicated by the rapid rise in 

 the radiation curve. 



The results show but little radiation in the region of 2 li, where pre- 

 viously a continuous spectrum was observed. It is also to be observed 

 that no strong emission lines occur at 1 p., where the alkali metals have 



intense lines. 



71 



Fig. 47- 



Nickel arc in hydrogen. 



