rr 



304 Mr. G. A. Hemsalech and the Comte de Gramont on 

 § 11. Summary of Results. 



1. A convenient method has been established of obtaining 

 the arc spectra of volatile metals. § 2. 



2. Experiments are described which seem to indicate that 

 spark lines are brought out in the arc when the degree of 

 ionization is lowered, as for example, by blowing air through 

 the arc. § 4. 



3. A very simple method has been developed of studying 

 the effect of various liquid media on the character of the 

 arc spectrum of a metal. This method consists in placing a 

 drop of the liquid between the poles before striking the 

 arc. § 5. 



4. The spark lines or so-called high temperature lines dis- 

 appear from the arc when the cathode is formed by white- 

 hot carbon. They are brought out prominently, on the other 

 hand, when the electrodes are cooled down to about — 190° C. 

 by immersion in liquid air. §§ 4 and 7. 



5. A detailed account has been given of the results of our 

 observations on the relative behaviour of different types of 

 lead and tin lines in the arc under various discharge condi- 

 tions. §§9 and 10. 



§ 12. Concluding Remarks. 



It has been shown in the course of this research that the 

 simple process of placing a drop of liquid between the elec- 

 trodes of an arc provides a very convenient method of 

 obtaining the spectrum of a metal vapour in which the spark 

 lines are prominent and easily recognized as such. In this 

 respect the liquid film arc resembles a capacity spark which 

 likewise brings into prominence lines of this type. But our 

 new arc method presents a decided advantage over the em- 

 ployment of capacity-sparks inasmuch as no air lines are 

 brought out with the exception of the not very obnoxious 

 lines of hydrogen. As is well known, the spectrum of a 

 capacity-spark is infested by hundreds of air lines, which in 

 many cases render the observation of the metal lines very 

 difficult, and although the introduction of self-induction into 

 the discharge circuit suppresses all the air lines, it also 

 similarly affects the spark lines. Thus it seems to us that 

 by further developing the new arc method, an* effective 

 means should be obtained not only of exciting spark lines in 

 metal vapours, but also of finding out more about their 



