14 CHAPMAN ON FLAME EEACTIONS. 



composition of Apophyllite is said "to agree very nearly with the formula 2H2O. CaO. 

 SiO_,, in which a small part of the hydrogen may be assumed to be replaced by potas- 

 sium." IrrespectiA'e however of the part actvially fulfilled by its H'O, the composition of 

 Apophyllite, as confirmed by the s]3ectroscoi3e reaction which forms the subject of the 

 present note, would appear to be more correctly indicated by the formula 4 (CaO, 2SiO-, 

 2H=0) +KF. 



(3.) The Red Line in the Spectrum of Potassium. — The detection of potassium in 

 the presence of sodium and other bodies by the examination of the flame reaction through 

 a blue glass or a solution of indigo — as indicated by Cartmell, many years ago — 

 whilst effective in the main, does not in all cases give absolutely satisfactory results. 

 But if the flame spectrum of potassium compounds be examined in this manuei-, no 

 erroneous or indefinite conclusion can by any possibility occur. The red line of this 

 spectrum, when viewed through a deep blue glass, remains altogether unafl'ected, or stands 

 out in full relief, whilst the yellow line (or double line) of sodium, the orange and red 

 lines of strontium, the red calcium line, and the vivid red liue of the lithium spectrum, 

 assuming these bodies to be present also in the substance under examination, are entirely 

 cut off" and obliterated. Minerals may thus be conveniently examined for potassium by 

 previous fusion with fluor spar (in default of ammonium fluoride), or with sodium 

 carbonate according to the method recommended by Bunsen for Orthoclase, as 

 the glare of the sodium spectrum and the red calcium line become entirely 

 destroyed and intercepted by the glass — provided, of course, that the colour 

 of the latter be not too pale. The question then arises as to the cause of 

 this phenomenon. The red potassium line referred to, is entirely within the red 

 band of the solar spectrum, coinciding practically with the A line of the latter. How, 

 then, does this red line pass through the blue glass, whilst the red lines of lithium, 

 strontium, and calcium are completely absorbed and intercepted ? If the blue glass be 

 sufficiently deep in colour, the phenomenon does not appear to be in any way affected by 

 the nature of the coloring matter. Can it be that the red band of the solar spectrum 

 consists really of two bands — a Aaolet-red or claret-red band at the commencement of 

 the visible spectrum, and a red band proper, forming the transition between this and the 

 orange zone ? 



(4.) MoLYBDic Anhydride. — Distinct and well marked flame-spectra are exhibited as 

 a rule by all substances which impart a colour to the flame of the blowpipe or Bunseu- 

 burner. Molybdenum compounds, however, form one of the exceptions, and perhaps the 

 most striking exception, to this rule. Molybdic anhydride or tri-oxide, which results 

 during the ignition of these compounds generally, communicates to the flame-border a 

 very distinct and characteristic yellowish-green coloration, but no line-spectrum is 

 manifested. This anomalous result appears to be at present without explanation. 



