240 Scientific Proceedings, Royal Dublin Society. 
is to be preferred to aqueous solutions, or to substances strongly 
acidified with hydrochloric acid. Thus the examination is simpli- 
fied and made more cleanly in manipulation. Any salt previous 
to being examined should be heated in a covered porcelain crucible 
until it ceases to decrepitate or evolve water; it is then in a 
suitable condition to be placed on the support. 
In the practical use of the flame-spectra there is no difficulty 
in recognizing traces of the alkalis by their lines; but with salts 
of the alkaline earth-metals, the most characteristic feature of their 
spectra are bands, and not lines. ‘The usual mode of examination 
in the Bunsen flame is to moisten the solid substance with 
hydrochloric acid, to take some of this up on a platinum wire and 
place it in the flame, when a momentary brilliant flash follows ; 
after a short interval very little of the spectrum remains to be 
seen, and what there is has an essentially different appearance. 
It is hardly necessary to point out that volatile metallic chlorides 
yield the first spectra; and those subsequently visible are the 
spectra obtained, first by the conversion of the chlorides into 
oxides, and secondly by the reduction of oxides to the metallic 
state and the coloration of the flame by the metals.’ 
By employing the high temperature of the Mecke burner even 
of the simple pattern, the second spectra are rendered constant 
for a long period, even if the oxides or sulphates are employed. 
Accordingly, what distinguishes the least trace of calcium is 
a red band and a green band, one on each side of the sodium 
line. Strontium yields two red bands and one orange band. 
As a rule, neither the blue line of calcium nor the corresponding 
blue line of strontium is plainly seen. Ii any calcium salt be © 
placed in the flame, the effect first seen is a strong sodium 
spectrum ; but the heat is so intense that the sodium is soon 
volatilised ; and nothing but the red colouration of the calerum 
remains; though this may continue for an hour or longer, and may 
be photographed. The red and green bands have been obtained 
from calcium chloride, calcium nitrate, calcium carbonate, calcium 
sulphate, and from quick-lime, ‘The photograph of the bands, 
taken from calcium nitrate during one hour’s exposure in a 
1«¢ On the Thermo-Chemistry of Flame-Spectra at High Temperatures,” Hartley, 
Proc. Roy. Soc., 1907, A, vol. lxxix., pp. 242-261. 
