IN RELATION TO QUANTITATIVE CHEMICAL ANALYSIS. 
61 
On the presence of impurities in certain spectra. 
It has been noticed that when solutions are photographed with a Leyden-jar in 
circuit, and when these solutions are concentrated, two very fine and continuous lines of 
a strong character, which have been identified with the metal calcium, are occasionally 
seen. Their wave-lengths are 3967'6 and 3933, and they are designated H and K of 
the solar spectrum on M. Cornu’s map. Sometimes a second pair of lines, with wave¬ 
lengths 3736 - 5 and 3705‘5, are visible. They appear in strong solutions of cadmium 
chloride, ferric chloride, cobaltic chloride, and ferric nitrate. They are of very feeble 
intensity in strontium chloride and barium chloride, and then only the first pair are 
visible, attenuated and shortened. 
They appear as short lines and rather feeble in photographs taken from electrodes 
of Siemens-Martin steel, and from electrodes of iridium. The most remarkable fact 
about these lines is, that they are not visible in the spectra of the alkaline chlorides, 
lithium, sodium and potassium, which were prepared from neutral solutions. Nor are 
they to be seen in the spectrum of aluminium chloride. They do not appear in photo¬ 
graphs of the spectra of graphite points, either when dry or moistened with water, but 
they are seen as very faint and short lines when graphite points are moistened with 
hydrochloric acid. They are fairly well seen in solutions of ferric sulphate, prepared 
by dissolving the oxide in sulphuric acid. For some time the origin of these lines 
was a source of some perplexity, for although they had been ascertained to be calcium 
lines, yet they made their appearance on occasions when they were least expected, and 
when their presence could not be accounted for. Acids were always found to contain 
traces of calcium, and particularly hydrochloric acid; but the quantity was so 
minute as to be capable of detection only by photographing the spectrum. A quantity 
of pure hydrochloric acid was distilled in a previously very carefully cleaned glass 
retort and collected in a glass receiver. The operation was so conducted that by no 
possibility could any of the liquid have been carried over, except in the form of vapour. 
Still, in photographs of the spectrum of the distillate, the calcium lines were detected 
but little diminished in intensity. When platinum wire was substituted for graphite 
electrodes the lines were again present. 
There is much evidence that the action of the acid upon the glass vessels dissolves 
out of the glass a small portion of calcium. The calcium lines are particularly strong, 
while those of the alkalies are just as weak. It is probable that the aluminium which 
does not appear would be less likely to enter into solution, and at the same time as 
the lines are not so strong as the calcium lines they would not be so easily rendered 
visible. Messrs. Parry and Tucker found that various samples of iron, after solution 
in hydrochloric acid and further chemical treatment, gave evidence of the presence of 
calcium. In this case the calcium probably was introduced by the acid, or at least a 
portion of it, and the strength of the lines was increased by the concentration 
of the solutions. It must, however, not be overlooked that both Siemens-Martin 
