2 Harriry & Ramace—Wave-lengths of Principal Lines in Spectrum of Gallium, 
We were under the necessity of obtaining a specimen of pure iron for the 
purpose of obtaining a spectrum of this metal perfectly free from gallium, 
manganese, and one or two other elements, such as chromium, with which it is 
usually associated. For this purpose we made use of the iron in a pulverulent 
form, which is separated from potassium ferrocyanide when this substance is 
fused with potassium carbonate, and the black powder is separated from the 
potassium cyanide by solution in water or alcohol, and afterwards washed and 
dried. We believe this to be the purest form of iron which has yet been made. 
To use it in the are, we are obliged to ram it into carbon tubes, by which 
treatment it is unfortunately contaminated with carbon, but we have not found 
other impurities introduced. We have used also the iron residue obtained by 
the simple ignition of potassium ferrocyanide, the carbon of which must be very 
pure. For oxyhydrogen flame spectra, it is rolled up in ashless filter-papers and 
burnt in the flame. 
From our knowledge of the spectrum of gallium and of the proportion present 
in the minerals containing it, we concluded that it would probably be useless 
attempting to find any lines in the solar spectrum other than the two well-known 
lines of waye-lengths about 4172 and 4033. We found that the less refrangible of 
these lines is nearly coincident with an iron line in the are spectrum of iron and 
in the solar spectrum, and that the second and more refrangible line is nearly 
coincident with an iron-manganese line in the solar spectrum. In a case of this 
kind, where the lines are very feeble and very closely adjacent to others, 
mere coincidence observed by photographing metallic spectra along with that 
of the sun is not so satisfactory as actually determining the wave-lengths by 
measurements. The following is a list of the photographs taken with the 
Rowland grating :— 
Plate I.—(1) Solar spectrum. 
(2) Blast furnace iron containing z;45>th of its weight of gallium, 
an are spectrum. 
These spectra cannot be considered as showing absolute coincidences with the 
gallium lines. The are spectrum contains a very large number of lines belonging 
to iron, but those of gallium are not distinctly visible, because the iron lines lie 
over them. 
Plate II.—(1) Spark spectrum taken from a solution of gallium chloride 
between platinum electrodes. Exposure 15 minutes. 
(2) Solar spectrum showing where coincidences might be looked for. 
This photograph gives the relative intensities of the two lines, the less 
refrangible being the stronger. 
