354 Mr. F. Bates on a New 



was found impossible to maintain an arc sufficiently free 

 from flicker to give satisfactory results. 



Another possible source experimented with is the quartz 

 cadmium vapour arc lamp, described by Lowry and Abram *. 

 This lamp is always unsatisfactory owing to two defects. 

 It is necessary to have it permanently connected to an air- 

 pump and to immerse the electrodes in water. If the 

 cadmium in a vapour lamp is sufficiently pure, the adhesion 

 between the cadmium and the quartz results in the de- 

 struction of the lamp upon the solidification of the cadmium. 

 An improved form of lamp has been brought out by Sand |. 

 In this type, the tendency of the cadmium to adhere to the 

 quartz walls is stated to be lessened by introducing into 

 the lamp a small amount of zirconia in the form of tine 

 powder. The cadmium is placed in a side tube connected 

 to the pump and the body of the lamp by a tube constricted 

 to three capillaries for the purpose of filtering the metal. 

 Additional filtering may be obtained by introducing a roll 

 of iron gauze. Extensive experiments by the writer with 

 this type of lamp have demonstrated that it is impracticable, 

 provided a pure cadmium spectrum is desired. The method 

 of filtering suggested is inadequate. The impurities intro- 

 duced into the lamp by this method of tilling undoubtedly 

 have, a tendency to prevent breakage, but effectively prevent 

 obtaining a relatively pure, intense cadmium spectrum. In 

 order to eliminate all oxide and other impurities from the 

 cadmium used in filling, it is necessary to carefully distil 

 the cadmium into the body of the lamp. Upon allowing the 

 lamp to cool, adhesion between the quartz and the metal 

 takes place in spite of the presence of the zirconia. If the 

 lain}) does not crack upon the first solidification of the 

 cadmium, thin sections of the quartz are peeled from 

 the walls by the contracting metal. Upon cooling a second 

 time, the lamp was invariably cracked. 



Numerous experiments of varied character failed to over- 

 come the constant breakage of the Sand lamp. Among the 

 filling mixtures tried was a cadmium-mercury alloy. The 

 percentages of the constituents were varied on a wide range. 

 The introduction of the mercury is very effective in pre- 

 venting the cracking of the lamp, as the alloy formed was so 

 soft that no appreciable adhesion between it and the quartz 

 resulted. It was found, however, impossible to obtain 

 a brilliant cadmium spectrum under any circumstances. 



* Trans. Faraday Soc. vol. x. p. 103 (1914). 



t Proe. Phys. Soc. London, vol. xxviii. p. 94 (1915-16). 



