836 Mr. Gr. A. Hemsalech and the Comte de Gramont on 



The second and third type lines constitute the so-called] 

 arc lines. 



In addition to a detailed account o£ our experiments with 

 magnesium the present communication contains also the 

 results of our observations on the enhanced lines o£ the 

 related elements zinc and cadmium. 



The methods of producing and of observing the various 

 kinds of arcs were the same as those described in our first 

 communication. 



§ 2. Influence of the nature of the liquid film upon the 

 emission of various types of lines in the arc. 



In an arc flash passing between magnesium poles through* 

 a liquid film the first phase is generally sharply defined, and 

 the character of the spectrum changes almost abruptly on. 

 passing from the first to the second phase. The relative 

 behaviour of the various types of magnesium lines is 

 probably controlled by the conditions which predominate at 

 the various stages of development of an arc flash. Thus, if 

 certain chemical reactions took place between the magnesium 

 vapour evolved and the liquid or one of its constituents, such. 

 an event might reveal itself by some special peculiarity of 

 the spectrum and the latter would change on passing from a. 

 liquid of one kind to one of a different chemical constitution.. 

 Again, if any particular group of lines were influenced by 

 the electric field set up within the first phase, the effect 

 should be the same for all liquids whatever may be their 

 composition. Of the three liquid films used with magnesium — 

 namely, water, glycerin, and paraffin oil, the first two contain 

 oxygen, and we might therefore expect to observe effects of 

 possible oxidation. Indeed we find that whereas in the 

 water and glycerin films the flame line 4571 is well deve- 

 loped, only faint traces of it are seen in the paraffin-oil film. 

 In like manner the well-known band at A, 5007, which is 

 generally ascribed to the formation of an oxide, is brought 

 out in the water and glycerin films but is absent from the 

 paraffin-oil film. In the second phase or the arcing stag'. 1 

 the flame line as well as the bands are brought out in all 

 three cases. During this phase the arc flash is of course 

 exposed to the influence of the surrounding air containing 

 oxygen. Thus, it would seem that the emission of the flame 

 line X4571 under these conditions is favoured, though not 

 solely controlled, by the presence of oxygen. 



The lines of the second type, namely the triplet series, on 

 the other hand, are not affected by the nature of the film.. 



