168 
PROFESSOR W. R. HARTLEY OH 
their mean path Is so extended that their motions become rhythmical. Reduce the 
freedom of their motions and the result is a continuous spectrum."^ 
Mitscherlich first drew attention to the distinct spectra, for the most part com¬ 
posed of bands, which are emitted by compounds (‘ PoGG. Annalen.,’ vol. 121, p. 459). 
Diacon also (‘Theses de Physique et de Chimie,’ Montpellier, 1864, Boehm et 
fils), using a flame the interior of which was fed with chlorine, obtained distinct 
spectra of chlorides such as those of the alkaline earths, also gold, lead, iron, cobalt, 
and nickel. 
The alkalies gave no spectrum except where the conditions were such that they 
became converted into oxide or metal, as in the nmntle of the flame. Of the various 
compounds examined, some gave degraded band sj^ectra, others plain bands, and 
many yielded line spectra, or bands and lines together, Plucker and Hittorf first 
showed that the alkali metals and their salts emit, even at a low temperature, spectra 
of the 2nd Order or lines, while metals of the alkaline earths, and compounds of the 
same emit band sj^ectra, accompanied by a principal line. When the bands are well 
developed they constitute a spectrum of the 1st Order ; this was proved in every 
respect to be the case with the band spectrum of barium. 
Flame Sjjectra Emitted l>y Conij^oviids at H'ujh Temperatures. 
I. Spectra of Elements. Chief y Lines. —Iron, nickel, cobalt, chromium, manganese, 
sodium, potassium, lithium, thallium, rubidium. 
II. Spectra Peculiar to Compounds. Lines and. Bands together. —Calcium oxide 
and salts, calcium fluoride, strontium oxide and salts, barium oxide and salts, 
beryllium oxide and salts, magnesium oxide and salts, aluminium oxide and salts, 
cadmium oxide and salts, copper oxide and salts, chromic trioxide, pdiosphorus 
pentoxide, cerium oxide and salts, cerium chloride. 
The study of the spectra of compounds is one of much interest, particularly in its 
bearings on the periodic law, and the prosecution of this subject is being continued. 
Application of the Oxy-hydrogen Flame Spectra to Chemical Analysis. 
Alkali Metals.— examination of insoluble minerals, such as silicates, in order 
to detect the alkali metals, may be readily made with the oxy-hydrogen blow-pipe. 
Proof of the presence of lithium and sodium in kyanite is evidence of this. My 
assistant, Mr. PvAMAGE, examined a microcline felspar from the granite of Dalkey, 
C”. Dublin, by fixing a piece of it iii the flame for half-an-hour while a photograph 
was taken. The lines of sodium, potassium, lithium, and rubidium were identified. 
Alkaline Earth Metals. —A piece of dolomite gave the lines and hands characteristic 
* See Professor ScHUSTiats Rrittsh Ass(jciafion Reporf, 1880. 
