Page:The American Cyclopædia (1879) Volume XV.djvu/264

 252 SPECTRUM ANALYSIS charged with lithium and sodium. A volatil- izable compound of any such element being hurned in or otherwise diffused through a flame, the incandescent particles of each com- municate to the general light of the flame an excess of certain rays, these appearing in the spectrum as brighter bands crossing it in cer- tain parts and having the exact colors proper to such parts, being generally different in situ- ation and hue for the different elements intro- duced into the flame, and always or generally the same for each element. Fig. 1 shows the spectra of various chemical elements, the sym- bols of which are given on the left of the spectra. The upper spectrum is that of the sun, and on it are drawn the dark lines of Fraunhofer. (Seo SPECTRUM.) These lines are extended downward and through the lower spectra, and they thus serve as a kind of scale to which to refer the luminous bands of these spectra. The colored spectral bands are de- signated by the letters of the Greek alphabet, and are named in order of their importance as characteristic of their re- spective spectra. When, however, a flame is thus colored, or charged with excess of certain rays, if through this the light of another and more brilliant flame colored with the same element is passed to be analyzed, it is seen that while the general illumination of the spectrum is in- creased, the previous bright lines character- izing the element aVe now replaced by dark lines or lines relative- ly very faint ; in a word, the spectrum char- acteristic of the given element is exactly re- versed. The lower dark portion of fig. 2 shows the two bright lines of the spectrum of scope, the instrument with which spectrum an- alysis is effected, see SPECTRUM.) In the prose- cution of the new field of research opened by these experiments, Prof. R. Bunsen soon be- came associated. When several elements which show systems of bright bands are at the same time in the flame, it is at least generally true that their several spectra coexist ; and the in- stances in which certain lines proper to dif- ferent elements coincide are as yet few. The spectrum of sodium consists of two approxi- mate bands in the yellow of the spectrum near the orange, and seven relatively very faint lines; and Bunsen has determined that by it the presence in a flame of less than the TFtf.m.Tnnr P art of a grain is detected. Of calcium, barium, strontium, potassium, and lithium, the least quantities detectible vary from ^.Vs-fr to -nnr.^syjnnr grain ; so that no other chemical test approaches this in delicacy. Among results of the new analysis are, the finding that lithium is in fact an element widely diffused in nature, and the discovery of sev- incandescent sodium vapor; the upper por- tion of the figure shows these lines reversed by the passage of the light from an incandes- cent solid through the vapor of sodium. (For an engraving and description of the spectro- Fio. 3. Coincidence of the Fraunhofer lanes with the Lines of Iron and Calcium. eral new metals. (See CAESIUM, INDIUM, RUBI- DIUM, and THALLIUM.) This method of analy- sis has proved of great service in metallurgical operations^ The application of the method to researches in solar physics will be briefly no- ticed under SUN. Kirchhoff, hav- ing satisfied himself that the bright lines characteristic of several of the metals correspond exactly in place with as many dark lines of the solar spectrum, as shown in fig. 3, infers that these dark lines are produced by a reversal similar to that above shown, and hence indicate the existence of corre- sponding chemical elements, both volatile in the luminous atmos- phere of the sun, and also in- candescent in its nucleus. The fol- lowing table by Angstrom shows the number of lines belonging to the elements named which corre- Fio. 2. Reversal of the Sodium Line (seen with the Spectroscope). spond with dark lines of the solar spectrum : Hydrogen. 4 Sodium.... 9 Barium... 11 Calcium... 75 Magnesium 4 + (3?) Aluminum.. . 2 Iron 450 Manganese. . 57 Chromium. . 18 Cobalt.. . . 19 Nickel 33 Zinc 2 Copper 7 Titanium 200