98 Prof. Liveing, On the spectra of Calcium Fluoride. [Dec. 8, 1877. 



in Poggendorf s Annalen, cxxxj. p. 160 ; but the spectra described 

 by Becquerel as produced by fluor when exposed to the red 

 rays of the solar spectrum, and attributed by him to the action 

 of heat, agree with the bands I have marked (a) and (/3). 



No. 2 is the diagram of the spectrum produced by fluor 

 moistened with hydrochloric acid in the flame of a Bunsen's 

 burner : when a solution of fluor in nitric acid is used only the 

 bands marked (a), (/S), (7) and that from (8) to (e) are seen, the 

 other lines being probably due to the chloride. I have thought 

 it worth while to call attention to this spectrum, because in 

 analysing silicates with the spectroscope it is frequently necessary 

 to decompose them with hydrofluoric acid or alkaline fluorides, 

 and the ordinary text-books do not indicate the existence of the 

 bright green band (7) which is very characteristic. Mr Schuster 

 has reminded me that A. Mitscherlich has described the spec- 

 trum of calcium fluoride (Pogg. cxxj.) ; but his diagram and 

 description do not give an adequate idea of the spectrum. He 

 makes the band (7) consist of two about equal and quite distinct 

 parts. It is true that it is divided in two by a fine dark line at 

 about one-third of the breadth of the band from the violet side, 

 but the division is only just visible with such spectroscopes as are 

 ordinarily used for chemical analysis : and it is to be noted that 

 the other green band (/3) is divided nearly in the middle by 

 a dark line more easily visible. These dark lines are, however, 

 both too fine to be represented in the woodcut. 



