CREW AND BASQUIN. — LUBIINOSITY IN THE ELECTRIC ARC. 839 



visible spectrum which is linear or characteristic. The followiug experi- 

 ments are an attempt to answer this question, Is it possible hy heat alone 

 to obtain the characteristic visible spectrum of a gas ? 



We wish to distinctly avow at the outset that our answer is not so 

 definitive as is to be wished. Having, however, perfected a practical 

 experimental method for maintaining a metallic vapor at an exceedingly 

 high temperature and isolated from electric infiuenee, — more exactly an 

 electric or magnetic field, — a report upon this part of the work, together 

 with several incidental results, is now submitted. 



The method employed to separate the electrical, chemical, and thermal 

 effects — or, more properly, to isolate the thermal effects — is as follows. 

 The process involves three steps : — 



(1) The use of an electric arc between chemically pure metallic poles. 



(2) The use of this arc in gas which is chemically inert with respect to 

 the electrodes. 



(3) The examination of this arc during a very minute interval of time 

 when the current is off the arc, and only after an interval in which 

 the self-induction effects have had time to die down and disappear. 



Metallic electrodes are used, since they are freer from impurities and 

 much less complicated, from a chemical standpoint, than carbon. 



This arc is then worked in an air-tight metallic box, and this box is 

 flooded with a gas which is chemically inactive towards the electrodes. 

 We have used principally iron poles in hydrogen. This hydrogen is pre- 

 pared electrolytically by a current varying from 10 to 20 amperes ; the 

 small box containing the arc is thus swept out continually by a current of 

 fresh and dry hydrogen amounting to 100 cc. per minute. On the way 

 to the arc this hydrogen is passed successively through two drying tubes 

 of strong sulphuric acid and phosphoric anhydride. 



It is not to be forgotten, however, that, while iron and hydrogen are 

 inactive with respect to each other at ordinary temperatures, the laws of 

 high-temperature chemistry and low-temperature chemistry are radically 

 different, so that there is always the possibility of some unknown chemical 

 action at the high temperature of the electric arc. The arc was viewed 

 through a glass window in one wall of the air-tight hood. 



To exclude the electric current for an instant and examine the hot 

 metallic vapor immediately afterwards, the following device was used. 



An alternating dynamo of 100 volts was employed to feed the arc. 

 But in series with the armature, and on the same shaft with the arma- 

 ture, were placed two interrupters, which cut out either all the positive or 

 all the negative parts of the alternating current. 



