and containing a solution of cupric sulphate in | ammonia. The general phenomena of fluorescence are described under FLUORESCENCE; we here add several discoveries made since the writing of that article by Prof. Morton of Hoboken. In a portion of his researches Prof. Morton had the cooperation of Dr. H. C. Bolton of New York, who undertook the chemical work in the investigations. Their attention was particularly directed to the fluorescent properties of the uranium salts. The total number of distinct salts produced and examined so far by these investigators is 75, not including numerous specimens treated in various ways to establish the existence and conditions of their several hydrates. This multiplication of facts has given great value to this research as compared with previous work in the same direction. Thus, where Becquerel has examined one double acetate, these investigators have examined 16; in place of his three double sulphates, they have 16; in place of one fluoride, six; and so on. The methods pursued in the examination of these uranium salts were the same as those of Stokes and Becquerel. The discoveries made by Morton were mainly due to the wider range of substances examined, which made it possible to form inductions and generalizations, and to the scrupulous attention paid to the purity of these substances. We note only the most important results, and refer the reader to the following original papers for additional information: "American Chemist," vols. iii. and iv.; "Chemical News," vol. xxviii. 1. By a comparison of the spectra of 17 acetates and double acetates of uranium in the solid state and in aqueous solutions, the remarkable fact was demonstrated that in the case of these bodies no double salt could exist in solution in water. further experiments of the same kind this law was extended to all the known salts of uranium. 2. It was proved that by the study of the fluorescent spectra the existence of a new and before unknown salt could be By 1 of fig. 10). By continuing the heating until the salt ceased to lose weight, a substance was obtained giving spectrum No. 3 of fig. 10. These results naturally suggested that the two spectra 1 and 3 belonged to the hydrated and anhydrous salts, and that spectrum 2 indicated FIG. 10. a mixture of the two. On heating the dried salt to low redness for a short time, another double spectrum, No. 4, was developed, which by a continuance of the same treatment was reduced to a new simple one, No. 5. Analysis of the product so obtained showed that it was an ammonio-diuranic sulphate, a salt before unknown and not likely to have been discovered by any other means, as contact with water at once reduces it to a mixture of the normal salt and uranic sulphate. 3. It was discovered that certain uranic salts were capable of combining with definite proportions of water to form certain hydrates not heretofore recog FIG. 11. recognized. Thus, on heating the ammonio- | nized, and that each of these hydrates yielded uranic sulphate to 100° C. for a short time, a perfectly distinct and characteristic spectrum. it was noticed that its fluorescent spectrum Thus, the double sulphate of sodium and uraassumed a duplicate character (see spectrum nium seems to form no less than five hydrates 2 of fig. 10), a new set of bands being add- with from one to five atoms of water respeced to those of the normal salt (see spectrum tively. These salts have not all been isolated, 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 monohydrate; 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 fluorescence 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. 5. It was found that heat had invariably 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 new ways by which these bodies may be produced, and has found that they yield by fluorescence a light which gives a continuous 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: anthracene, 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 thallene, 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 ST, on the thallene, does not appear, from 8 of the scale upward, blue, indigo, and violet, but appears green of varying intensity. The energy 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 containing them to the spectra obtained from flames in which such substances are sublimed or volatilized. In reference to the solar spectrum and the transverse dark bands or lines of Fraunhofer marking it, see SPECTRUM; see also SUN. In 1802 Wollaston prepared the way for the discoveries of Fraunhofer, Kirchhoff, and others, by the invention of a new method of observing the solar spectrum. He admitted the solar rays into a dark room through a narrow slit, and placing him self at a distance of 12 ft. or more he viewed this slit through a prism of homogeneous glass held close to the eye. This method of observation shows the spectrum crossed transversely to its length by dark lines and bands; and hence the spectrum from a prism of given material and angle becomes a sort of scale or 10 20 map, to a fixed position in which every gradation of hue and every dark band can be exactly referred. Among the observations upon the spectrum, partially anticipating Kirchhoff's principle, were those of Fraunhofer (1815), of Talbot (1826), of Brewster (1832), of Wheatstone (1835), and of Foucault (1849). In 1855 30 40 50 60 70 80 90 100 110 120 130 140 150 160 170 Ka Na Li FIG. 1.-Table of Spectra according to Kirchhoff and Bunsen. Prof. A. J. Angström of Sweden, applying Euler's principle of the reciprocation and absorption by bodies of the same sorts of undulations which they are capable of emitting when themselves originally excited, was led to the view that any body at a glowing heat emits the 10 same rays (refrangibilities) of light and heat as, in the like condition, it will absorb if they impinge upon it. The first decisive and general proof in reference to light of the principle assumed by Euler and Angström was furnished by Kirchhoff's experiments in 1859, with flames charged with lithium and sodium. A volatilizable compound of any such element being burned in or otherwise diffused through a flame, the incandescent particles of each communicate to the general light of the flame an excess of certain rays, these appearing in the spectrum as brighter bands crossing it in certain parts and having the exact colors proper to such parts, being generally different in situation and hue for the different elements introduced into the flame, and always or generally the same for each element. Fig. 1 shows the spectra of various chemical elements, the symbols 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. (See 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 designated by the letters of the Greek alphabet, and are named in order of their importance as characteristic of their respective 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 increased, the previous bright lines characterizing the element are scope, the instrument with which spectrum analysis is effected, see SPECTRUM.) In the prosecution of the new field of research opened by these experiments, Prof. R. Bunsen soon became 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 instances in which certain lines proper to different elements coincide are as yet few. The spectrum of sodium consists of two approximate 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 180.000.000 part of a grain is detected. Of calcium, barium, strontium, potassium, and lithium, the least quantities detectible vary from 0 to 100.000.000 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 FIG. 3.-Coincidence of the Fraunhofer Lines with the Lines of Iron and Calcium. eral new metals. (See CESIUM, INDIUM, RUBIDIUM, and THALLIUM.)-This method of analysis has proved of great service in metallurgical operations. The application of the method to researches in solar physics will be briefly no spond with FIG. 2.-Reversal of the Sodium Line (seen with the Spectroscope). incandescent sodium vapor; the upper portion of the figure shows these lines reversed by the passage of the light from an incandescent solid through the vapor of sodium. (For an engraving and description of the spectro Hydrogen. 4 Sodium.... Barium... 11 Calcium... 75 ticed under SUN. Kirchhoff, having 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 corresponding chemical elements, both volatile in the luminous atmosphere of the sun, and also incandescent in its nucleus. The following table by Angström shows the number of lines belonging to the elements named which corredark lines of the solar spectrum: Aluminum... 2? Nickel....... Magnesium 4+ (3?) Cobalt... 19 Zinc.. Copper.. 83 Titanium..... 200 -Spectroscopic analysis applied to the stars has shown that they resemble the sun in general constitution and condition. But characteristic differences exist, insomuch that the stars have been divided into four orders distinguished by their spectra, types of which are given in fig. 4. These are thus presented by Secchi, who examined more than 500 star spectra: The first type is represented by a Lyræ, Sirius, &c., and includes most of the stars shining with a white light, as Altair, Regulus, Rigel, the stars B, 7, 8, 59 and of Ursa Major, &c. These give a spectrum showing all the seven colors, and crossed usually by many lines, but always by the four lines of hydrogen, very dark and strong. The breadth of these four lines indicates a very deep, absorptive stratum at a high temperature and at great presNearly half sure. the stars observed by Secchi showed this spectrum. The second type in cludes most of the yellow stars, as Capella, Pollux, Arcturus, Aldebaran, a Ursa Majoris, Procyon, &c. The Fraunhofer lines are well seen in the red and blue, but not so well in the yellow. The resemblance of this spectrum to the sun suggests that stars of this type resemble the sun closely in physical constitution and condition. About one third of the stars observed by Secchi showed this spectrum. The third type includes Antares, a Orionis and a Herculis, ẞ Pegasi, Mira, and most of the stars shining with a red light. The spectra show bands of lines; according to Secchi there are shaded bands, but a more powerful spectroscope shows multitudes of fine lines. The spectra resemble somewhat the spectrum of a sun spot, and Secchi has advanced the theory that these stars are covered in great part by spots like FIG. 4.- Secchi's Types of the Fixed Stars. those of the sun. About 100 of the observed stars belong to this type. The fourth type differs from the preceding in the arrangement and appearance of the bands. It includes only faint stars. A few stars, as y Cassiopeiæ, |