502 SPECTROSCOPIC SPECTRA. 



yellow, compounds of lithium a red line, of calcium an 

 orange and a green line. The spectra of these substances 

 are represented in fig. I. of the coloured frontispiece. 

 The compounds of potassium impart a pale violet tint 

 to the non-luminous part of the gas or hydrogen flame, 

 but the light emitted by their vapours is partly red, 

 partly violet, and partly a mixture of the colours of the 

 middle part of the spectrum. The spectrum must 

 hence show a red and a violet line ; these two lines 

 are, however, at the extreme ends of the spectrum, and 

 are so faint that they are only seen with difficulty. In 

 our spectroscope only the red line is well perceived, in 

 fig. I. therefore only the red one is shown. For eva- 

 poration in the flame, the .above-mentioned potassic 

 carbonate, or crude 'potash,' is best adapted; it must 

 be kept in a stoppered 'bottle because it is deliquescent, 

 that is, it attracts moisture from the air, and dissolves. 

 For the experiments a pretty large quantity should be 

 taken up with the platinum wire, as the salt evaporates 

 easily. Many other substances, for example, the com- 

 pounds of strontium and barium, when evaporated in 

 the flame, produce more complicated spectra, which, 

 however, still consist of single lines. Some of these 

 lines are so near to one another, that is, some of the 

 colours emitted by them in the state of vapour differ so 

 little in their refrangibility, that their edges touch one 

 another when viewed through so simple a spectroscope 

 as ours, and they appear as bands with coloured stripes. 

 In the spectrum of strontium especially are to be seen 

 a fine broad red band, an orange stripe, and a beautiful 

 'blue line ; the latter is only-distmctly observed at a suffi- 

 ciently high temperature, such as that of the hydrogen 



