250 SPECTKUM SPECTRUM ANALYSIS but fig. 11 shows the spectra of some of them. Thus No. 1 of the figure is the spectrum of the pentahydrate ; No. 2, that of a mixture of three hydrates ; No. 3, that of the monohy- drate ; and No. 4, that of the anhydrous salt. 4. In the case of the double acetates it appears that the position of their bands both of fluo- rescence and of absorption has a close relation to the atomic weights of the salts. Thus, a list of these salts in the order in which their bands occur, beginning with those which are highest in the spectrum, will be essentially a list of the salts in the order of their atomic weights. 6. It was found that heat had in- variably the effect of sending toward the red end of the spectrum all spectral bands of solids and of solutions in all cases where any effect could be observed. In a later memoir Prof. Morton, having investigated the fluorescent relations of the basic salts of uranic oxide, has shown many now ways by which these bodies may be produced, and has found that they .-yield by fluorescence a light which gives a con- tinuous spectrum. The latter property affords a ready means of distinguishing them, when either alone or in mixture, from hydrates and uranates, which they otherwise often resemble. The same methods of investigation have been applied by Prof. Morton to the following solid hydrocarbons found in the latter products of the destructive distillation of coal tar : anthra- cene, chrysogen, pyrene, and chrysene. He has also discovered a new hydrocarbon of very remarkable fluorescent properties occurring in the products of the destructive distillation of the heavier petroleum oils ; to this he has given the name of thallene, from the vivid green color of its fluorescent light. When a continuous spectrum is thrown on a screen of white paper, half of which is coated with thal- lene, the effect indicated in fig. 12 is seen. The portion R V, on the paper, shows the usual solar spectrum from red to violet, but the part S T, on the thallene, does not appear, from 8 of the scale upward, blue, indigo, and violet, but appears green of varying intensity. The energy the side of a tank containing a solution of thal- lene in benzole, the appearance indicated in fig. 13 is seen. The trails of light are of the following colors : olive green, bright emerald green, sky blue, and indigo running into violet. The value of the applications of spectrum anal- FIG. 12. of the fluorescent action of this body makes it available for some very striking illustrations Thus designs painted in it on muslin may bo invisible in yellow light, but flash out with a Murninous light when violet light falls upon tnem. When a pure spectrum is thrown on FIG. 13. ysis to fluorescent phenomena, as developed by Prof. Morton, consists in its opening a new method for investigating chemical and physical changes in bodies while these changes are in progress, and under conditions which would seem to exclude all other means of examination. SPECTRUM ANALYSIS, the name given to a recent method of chemical analysis, conceived and proposed in general form by Prof. G. Kirchhoff of Germany, in which the presence of certain chemical elements is determined by corresponding and peculiar sets of colored bands, imparted by those elements or compounds contain- ing them to the spec- tra obtained from flames in which such substances are sub- limed or volatilized. In reference to the solar spectrum and the transverse dark bands or lines of Fraunhofer mark- ing it, see SPEC- TRUM; see also Sux. In 1802 Wollaston pre- pared the way for the discoveries of Fraun- hofer, Kirchhoff, and others, by the invention of a new method of observing the solar spec- trum. He admitted the solar rays into a dark room through a narrow slit, and placing him-
