2 Hartley & Ramage — Wave-lengths of Principal Lines in Spectrum of Gallium, 



We were iincler tlie necessity of obtaining a specimen of pure iron for the 

 jDurpose 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 jjurpose 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 lias yet been made. 



To use it in tlie arc, 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 tlie 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 wave-lengths about 4172 and 4033. We found that the less refrangible of 

 these lines is nearly coincident witli an iron line in the arc 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 a-o^o-Trth of its weight of gallium, 



an arc spectrum. 



These spectra cannot be considered as showing absolute coincidences with the 



gallium lines. The arc 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 chloi'ide 

 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. 



