506 THE RARER METALS AND THEIR ALLOYS. 



degrees more may readily be attained iu a furnace of this kind. Each 

 pole is soon surrounded with a lambent halo of the green-blue hue of 

 the sunset, the central band of the arc changing rapidly from peach blos- 

 som to lavender and purple. The arc can then be lengthened, and as 

 the poles are drawn farther and farther asunder the irregular masses of 

 chromium fuse in silver droplets below an intense blue field of light, 

 passing into green of lustrous emerald. Then the last fragments of 

 chromium melt into a shining lake, which reflects tbe glowing poles in 

 a glory of green and gold, shot with orange hues. Still a few minutes 

 later, as the chromium burns, a shower of brilliant sparks of metal are 

 projected from the furnace, amid the clouds of russet or brown vapors 

 which wreath the little crater, while if the current is broken and the 

 light dies out you wish that Turner had painted the limpid tints and 

 that Ruskin might describe their loveliness. 



The effect when either tungsten or silver (fig. 2, PI. XXIV) replaces 

 chromium is much the same, but, in the latter case, the glowing lake is 

 more brilliant in its turbulent boiling, and blue vapors rise to be con- 

 densed in the iridescent beads of distilled silver which stud the crater 

 walls. 



Such experiments will probably lend a new interest to the use of the 

 arc in connection with astronomical metallurgy, for, as George Herbert 

 said long ago, 



Stars have their storms even in a high degree, 

 As well as we ; 



and Lockyer has shown how important it is, in relation to such storms, 

 to be able to study the disturbances in the various strata of the stellar 

 or solar atmosphere. Layers of metallic vapor whicli differ widely in 

 temperature can be more readily obtained by the use of the electrical 

 furnace than when a fragment of metal is melted and volatilized by 

 placing it in the arc on the lower carbon. 



It must not be forgotten that the use" of the electric arc between 

 carbon poles renders it practically impossible to prepare the rare 

 metals without associating them with carbon, often forming true car- 

 bides; but it is possible in many cases to separate the carbon by sub- 

 sequent treatment. Moissan has, however, opened up a vast field of 

 industrial work by placing at our disposal practically all the rarer 

 infusible metals which may be reduced from oxides, and it is necessary 

 for us now to consider how we may best enter upon our inheritance. 

 Those members of the group which we have known long enough to 

 appreciate are chromium and manganese, and these we have only known 

 free from carbon for a few months. In their carburized state they 

 have done excellent service in connection with the metallurgy of steel; 

 and may we not hope that vanadium, molybdenum, titanium, and 

 uranium will render still greater services'? My object in this lecture is 

 mainly to introduce you to these metals, which hitherto few of us have 

 ever seen except as minute cabinet specimens, and we are greatly 



