128 REPORT—1883. 
when spectra were taken from solutions, so that discontinuous lines 
became long or continuous lines. 
A few instances of short lines disappearing have also been noticed, 
but such disappearances occur only when the lines are so short, mere dots 
in fact, that no solution can contain a quantity of the metal sufficient to 
yield an image of them, unless the rest of the spectrum be greatly over- 
exposed. Certain very short lines in the spectrum of zinc are an example 
of this. Very short lines in the spectrum of aluminium were not repro- 
duced by solutions of the chloride unless the solutions were highly con- 
centrated. It may thus be seen that the quantity of metal present in the 
compound thus determines the presence of the lines. 
The lengthening of short lines—It was remarked that in certain cases 
metallic electrodes showed a different spectrum according to whether the 
spark was passed between dry or wet electrodes. Thus it was pointed 
out that when iridium electrodes are moistened with calcium chloride, 
discontinuous lines which are very numerous in this spectrum became 
continuous, and on further examination into this matter it has been found 
that even moistening with water has the same effect. Hence the supposi- 
tion, of which there seemed some possibility but no proof, that a chloride 
of the metal was formed was found to be untenable. The very short lines in 
the spectrum of zinc were lengthened by the action of water upon the elec- 
trodes. It has now been proved beyond doubt that this peculiar varia- 
tion in the spectra is caused by the cooling action of the water upon the 
negative electrode, which in effect is the same as a strengthening of the 
spark, since by heating the electrodes a reverse action is the result. 
Alterations in the spectrum of carbon.—As already stated in the previous 
Report, graphite electrodes have been generally employed for the purpose 
of producing spark spectra from solutions. A portion of the work in 
connection with this subject included an investigation of the effect of 
water and of saline solutions in varying the spectrum of carbon. It will 
of course be readily seen that, as carbon is capable of combining with 
oxygen and nitrogen, different spectra might be obtained by making 
one or other of those gases the atmosphere surrounding the electrodes, 
but it is not so easy to explain why graphite points should give two dif- 
ferent spectra in air when dry and a third spectrum when moistened 
with water, the same spark conditions being maintained. Three such 
spectra have been photographed, but without the aid of maps their 
peculiarities are not capable of exact description. The maps which were 
drawn were presented to the Royal Society together with a communi- 
cation on this subject, three months since, so that they are not at present 
available. It may be said, however, that the difference between the 
spectra taken from dry electrodes in air consists in the omission of a 
certain number of the less refrangible lines, which have undoubtedly 
been identified with carbon. 
Spectra of the non-metallic constituents of salts—A long series of expe- 
riments has been made with the object of determining the non-metallic 
elements which are capable of yielding spark spectra when in combina- 
tion with the metals. Chlorides, bromides, iodides, sulphides, nitrates, 
sulphates, selenates, phosphates, carbonates, and cyanides yield nothing. 
On the other hand, solutions in hydrochloric acid of arsenites, arseniates, 
and antimoniates yield spectra of arsenic and antimony respectively. 
Borates and silicates in solution yield very characteristic spectra of the 
non-metallic constituents; but if the solutions be prepared from sodium 
