72 



INFRA-RED EMISSION SPECTRA. 



(b) SPARK SPECTRA OF METALS LN HYDROGEN. 



For producing a high potential spark (arc) a 10,000- volt transformer, 



with 100 volts, 1 to 9 amperes in the primary, 

 was used. From one to three glass condenser 

 plates, each having a capacity of 0.0028 M.F., 

 was placed in parallel with the electrodes. This 

 produced a very intense arc. An image of the 

 electrodes was projected upon the spectrometer 

 slit by means of a short focus, concave mirror. 

 The electrodes were about 3 mm. diameter, filed 

 wedge-shaped. They were mounted in glass 

 holders which were fitted into a glass vessel of 

 about 200 c.c. capacity by means of ground 

 joints (designed by Dr. Nutting), which per- 

 mitted adjustment of the electrodes as shown in 

 fig. 48. The radiation passed through a quartz 

 window about 3 mm. thick, hence opaque be- 

 yond 4 ft. The hydrogen was prepared electro- 

 lytically in an automatic 

 glass generator shown in 

 fig. 49. 



The spark (arc) spectra 

 of the following metals 

 were examined : alumi- 

 num, copper, and calcium. For electrodes of the 

 latter, thin pieces were sawed from a large bar of 

 the metal, which were then hammered into wires 

 about 2 to 3 mm. in diameter. These were kept 

 under oil to prevent oxidation. The result of the 

 examination was rather disappointing, for no ap- 

 preciable radiation could be detected up to 3.5 to 

 4 fi, where the electrodes gave from 3 to 10 cm. 

 deflections. This latter was eliminated by covering 

 the spectrometer slit over the whole length, except fjo. 49. Automatic ciectro- 



1 ,., v.i 1,1 t- lytic hydrogen generator. 



about 2 mm., which permitted only the radiation 



from the high potential arc (spark) to enter the instrument. The fact 

 that no deflections greater than 1 mm. were observed is not due to a lack 

 of sensitiveness of the instrument, and it may be concluded that no emis- 

 sion lines were produced which had an appreciable intensity. This is 

 rather surprising, for calcium is close to the group of elements having 

 emission lines in the infra-red. 



Fig. 48. Hydrogen spark tube. 



