148 
ME. W. HUGGINS ON THE SPECTRA 
With both these salts the pairs at 820 and 1170 were satisfactorily observed, though it 
was with some difficulty, and only by occasional glimpses. 
I then compared the sodium-spectrum directly with that of the sun. So numerous 
are the fine lines of the solar spectrum, and so difficult is it to be certain of absolute 
coincidence, that I hesitate to say more than that the pair of lines 818 and 821 appeared 
to agree in position with Kirchhoff’s lines 864-4 and 867T ; and of the pair 1169 and 
1174, one appears to coincide with a line sharply seen in the solar spectrum, but not 
marked in Kirchhoff’s Map, which would be about 1150-2 of his scale, and the other 
with Kirchhoff’s line 1154-2. The other pair and the nebulous band are too faint to 
admit of satisfactory comparison with solar lines. 
11. Potassium . — When commercial potassium is employed as an electrode, about 16 
lines are seen in addition to the pair near A of the solar spectrum. Four quite distinct 
specimens of potassium gave identical results, the same lines being visible in all, and no 
other lines. I then prepared by electricity an amalgam of potassium, but, with the 
exception of the line 840 occasionally visible, the lines were not seen. As the potas- 
sium lines are fainter than those of sodium, this negative result does not appear to be 
conclusive, since the great intensity of the mercury-spectrum might overpower the feebler 
lines of potassium, especially when this was present only in small quantity and not in 
the concentrated metallic form. One electrode was then surrounded with cotton con- 
taining concentrated solution of chloride of potassium, and afterwards with cotton con- 
taining that of caustic potash. With both these, rather more easily with the latter, 
the lines 840, 1049, 1065, and 1073 were occasionally and faintly perceived. 
[This great diminution in the brilliancy and number of the lines when, in the place 
of metallic potassium, solutions of its salts are substituted, may be due to the unfavour- 
able condition of the latter for the production of potassium vapour. The large volume 
of the gases formed by the decomposition of the water must disperse and attenuate the 
comparatively small volume of vapour of the element forming the base of the salt, and 
also the great expansion in the gaseous state of the constituents of the water would 
lower the temperature of the vapour of potassium mingled with them. The salts should 
be subjected to the discharge free from water, and in a condition in which they conduct 
the current. If dry, or fused upon the wires, they are disrupted and scattered. 
A platinum wire was coiled at one extremity into a little cup-like cage. Chloride of 
potassium was placed in this and fused. This wire, with the fused bead of chloride, was 
placed above the platinum wire forming the other electrode. A spirit-lamp is placed 
beneath the wires ; as soon as the bead is in a state of fusion, the lamp is withdrawn 
and contact immediately made. During the few seconds that the chloride remains 
fused, most of the lines of metallic potassium are seen. Of the lines 1328 and 840 the 
observation is less certain, and is very doubtful of 763 and of 727. 
Protochloride of tin similarly employed gives a brilliant spectrum of tin. — Feb. 1864.] 
12. Calcium . — The spectrum was obtained from electrodes of metallic calcium, sup- 
plied to me by Dr. Matthiessen. The colour of the spark, as seen by the eye, is bril- 
