304 Royal Society : — Dr. W. Huggins on the Spectra 



line of Fraunhofer's b, which distinguishes magnesium, and the other 

 with a group of bright lines which is seen between b and F, nearly in 

 the position of the brightest double line of nitrogen, when metallic 

 magnesium is burnt in air. 



The chloride formed from magnesium, when introduced into the 

 Bunsen flame, gave the same bands ; but the more refrangible band 

 was exceedingly faint. 



When an induction-spark was taken from a wire covered with 

 cotton-wool soaked with a solution of the chloride, the lines at 6 

 and the more refrangible group were seen. If the heating-power of 

 the spark be increased by the introduction of a Leyden jar, the 

 band between b and F becomes scarcely distinguishable, while the 

 lines peculiar to metallic magnesium are much more intense. When 

 a spark was taken between electrodes of the same specimen of magne- 

 sium from which the chloride was formed, no trace of this band was 

 detected. 



Baryta. — When pure caustic baryta is subjected to the heat of 

 the oxyhydrogen flame, a brilliant spectrum is seen identical with 

 the well-known spectrum which presents itself when chloride of ba- 

 rium is heated in the Bunsen flame. Baryta furnishes a larger quan- 

 tity of vapour than lime and magnesia, and therefore the lines could 

 be traced to a greater distance from the solid baryta. 



Strontia. — Pure strontia was fused into a large bead upon a 

 platinum wire. When this bead was heated by the oxyhydrogen 

 flame, the same spectrum of bright lines presented itself as is seen 

 when chloride of strontium isplaced in the flame of a Bunsen' s burner. 



Zirconia. — One of the small pellets of zirconia prepared in France 

 for use with the oxyhydrogen blowpipe was found to give no trace of 

 bright lines. This great fixity of zirconia as compared with lime is in 

 agreement with the inalterability of the substance under the action of 

 the oxyhydrogen flame. 



Alumina. — Pure alumina treated in the same way as the magnesia 

 gave a continuous spectrum only, without any trace of bright lines. 



Glucina. — Glucina gave a bright line in the red, which I found 

 to be due to potassium. Glucina, therefore, appears not to form 

 vapour of any kind under the heat of the oxyhydrogen blowpipe. 



Titanic acid gave a continuous spectrum without lines. 



Oxide of uranium a continuous spectrum without lines. 



Tungstic acid a continuous spectrum without bright lines. 



Molybdic acid a continuous spectrum without bright lines. 



Silica (precipitated) a continuous spectrum without bright lines. 



Oxide of cerium a continuous spectrum without bright lines. 



The question presents itself as to the nature of the vapour to which 

 the bright lines are due in the case of the earths lime, magnesia, 

 strontia, and baryta. Is it the oxide volatilized ? or is it the vapour 

 of the metal reduced by the heat in the presence of the hydrogen of 

 the flame ? The experiments show that the luminous vapour is the 

 same as that produced by the exposure of the chlorides of the metals 

 to the heat of the Bunsen gas-flame. The character common to 

 these spectra, of bands of some width, in most cases gradually shading 



