HartiEy—On the Spectra of Calcium and Magnesium. 245 
The question arises, I’o what extent can foreign substances in 
the calcium affect the spectrum? ‘Traces of lithium and sodium 
are present; but such minute quantities of these metals can have 
no influence. ‘The calcium undoubtedly contains a small quantity 
of carbide, because the gas which is evolved by its interaction 
with water has the odour of acetylene; but since the hydrogen 
burns without any perceptible illumination, such as would proceed 
from an admixture with a gas so rich in carbon, the amount is 
probably very small. There is a possibility of calcium hydride 
being an impurity; but to what extent this substance can affect 
the discharge of electricity is not known. 
Magnesium.—When photographing magnesium metal with 
sparks passing in a closed vessel at a reduced pressure of 5 mm., 
similar observations were made of stationary bright spots and 
scintillations, with an occasional very brilliant green flame. The 
sparks passed with greater regularity than was the case with 
calcium in like circumstances. 
When the current was first turned on, the sparks had a yellow 
or orange colour; the brilliant green rays appeared subsequently. 
With the eye, bands in the citron green and an orange line were 
visible with two brilliant green lines close together. A photograph 
taken of the spectrum of the spark without condenser, and an 
exposure of twenty minutes with a narrow slit, yielded nothing 
beyond the two intensely green lines, with wave-lengths approxi- 
mately 5209 and 5200. 
Another photograph taken in the same manner yielded the 
two lines in the green, with a faint indication of a narrow band a 
little more refrangible than 5200, and degraded on the more 
refrangible edge. This corresponds with the head of the fluted 
band in the magnesium spectrum on Plate XXX. of ‘Banded 
Flame Spectra of Metals’’;! but there is, in addition, a series of 
nitrogen bands in the region lying between wave-lengths 4000 
and 3600, and a group of bands like strong, broad lines, termi- 
nating in two lines. 
The lines and bands have not been photographed from 
magnesium in an atmosphere of hydrogen at normal pressures. 
They appear to be variable even under apparently identical 
1 Hartley and Ramage, Trans. Roy. Dublin Soc., 1901, vol. vii., part 12, p. 339. 
