The lines of the spectrum show themselves most plainly when the temperature of the flame is highest and its illuminating power least; hence a hydrogen gas burner, which gives a feeble illumination with great heat, is best adapted for the purpose of experimenting.

The apparatus employed by Messrs. Kirchhoff and Bunsen in their observations is thus described in Poggendorff's Annalen. (See figure.)

A is a box blackened on the inside, having its horizontal section in the form of a trapezium, and resting on three feet; the two inclined sides of the box, which are placed at an angle of about 58° from each other, carry the two small telescopes B and C. The eye-piece of the first telescope is removed, and in its place is inserted a plate, in which a slit made by two brass knife-edges is so arranged that it coincides with the focus of the object-glass. The gas lamp D stands before the slit in such a position that the mouth of the flame is in a straight line with the axis of the telescope B. Somewhat lower than the point at which the axis of the tube produced meets the mouth, the end of a fine platinum wire bent round to a hook is placed in the flame. The platinum wire is supported in this position by a small holder, E, and on to the hook is melted a globule of the metal or salt of the metal which it is desirable to examine. Between the object-glasses of the telescopes B and C is placed a hollow prism, F, filled with bisulphide of carbon, and having a refracting angle of 60°; the prism rests upon a brass plate, movable about a vertical axis. The axis carries on its lower part the mirror G, and above that the arm H, which serves as a handle for turning the prism and mirror. A small telescope placed some way off is directed toward the mirror, and through this telescope an image of a horizontal scale fixed at some distance from the mirror is observed. By turning the prism round, every color of the spectrum may be made to move past the vertical wire of the telescope C, and any required position of the spectrum thus brought to coincide with the vertical line. Each particular portion of the spectrum thus corresponds to a certain point on the scale. If the luminosity of the spectrum is very small, the wire of the telescope C may

be illuminated by means of a lens, which throws a portion of the rays from a lamp through a small opening in the side of the tube of the telescope C.

The metals experimented on by Messrs. Bunsen and Kirchhoff are used in the form of chlorides purified with the greatest care. When these are introduced into a jet of flame they volatilize to a greater or less extent, and then communicate to the flame the special character above alluded to.

=

35.3

Of the wonderful delicacy of this new method of analysis, our readers may obtain a realizing sense from the following description of an experiment which a recent writer describes as witnessing in Prof. Bunsen's laboratory. In a far corner of the experiment room, the capacity of which was about 60 cubic metres (1 cubic metre cubic feet), was burnt a mixture of 3 milligrammes (0.0462 gr.) of chloride of sodium (common salt), whilst the spectrum of the flame was observed through the slit of the telescope. Within a few moments, when the vapor has time to diffuse itself throughout the lamp flame, a bright and distinct yellow line was seen to cross the spectrum, which remained visible for a few minutes and then disappeared. This was the sodium line; for whenever sodium is present in the atmosphere of the lamp flame, and however combined with other substances, that particular line never fails to appear. In this experiment, it was calculated, from the weight of the sodium salt burnt, and from the capacity of the room, that there was present, suspended in one part by weight of air supplied to the flame, less than one 20,000,000th of a part of chloride of sodium vapor. But as the reaction of the sodium on the spectrum could be easily observed in one second, and as in this time the quantity of air heated by the flame could be calculated from the rate of issue from the flame, and from the composition of the flame, the surprising result was arrived at that the eye, in this experiment, was able to recognize with the greatest ease the presence of the three-millionth part of a milligramme of chloride of sodium. It must not, therefore, be a matter of surprise to find sodium distributed almost everywhere, especially in the atmosphere, in which is almost always a sufficient quantity to show the sodium ray. The same may be also said in a great measure of the rare metal lithium, which gives two sharply-defined lines-the one a very weak yellow line, and the other a bright red line, both toward the extreme end of the solar spectrum.

In regard to the sensibility of the lithium reaction in the spectrum analysis, it is stated that in a room of a capacity of about sixty cubic metres was exploded a mixture of sugar-of-milk and chlorate of potassa, containing nine milligrammes of carbonate of lithia. The lamp, being placed at some distance off, became quickly colored, so that the red ray could be distinctly visible in the spectrum. The authors estimated that this sensibility reached the nine-millionth part of the amount taken.

Messrs. Bunsen and Kirchhoff found in their experimenting, greatly to their surprise, that lithium, instead of being a very rare substance, was one of the most widely distributed of the elements. They found it in the water of the Atlantic; in the ashes of marine plants; in pure spring water; in the ashes of tobacco, vine leaves, and of grapes;

and even in the milk of animals fed on crops growing in the Rhine plain, on a non-granite soil, and in the human blood. In the motherliquors of tartaric acid manufactories, the lithia is found to be so concentrated as to be worth commercial extraction; and the same may be said of certain mother-liquors of saline springs.

The spectrum reaction of potassium is not nearly so delicate as that of sodium; its spectrum yielding only two characteristic lines, one in the outermost red, and the other far in the violet ray of the solar spectrum-points at which the eye ceases to be sensitive to the rays. The presence, however, of one thousandth of a milligramme of the metal could be readily detected.

The rays shown by the chlorides of barium, strontium, and calcium are more complicated than those afforded by potassium, sodium, and lithium, and require a somewhat experienced eye for their identification. They are, however, quite distinct enough to be easily recognized, even when salts of these metals are mixed together; for the great advantage of this method of analysis is, that foreign matters have no influence on the results, the chemists being able to detect with certainty the different elements in a mixture containing the tenth of a milligramme of the metals mentioned above. Sodium, with its yellow ray, first appears; after that the well-defined red ray of lithium; next is seen the paler rays indicating potassium; and, after these rays have disappeared, they are replaced by those of calcium and strontium, which remain visible for some time. The absence of one or other of these sets of rays shows the absence of the corresponding metals.

We are, then, by this method, placed in possession of an analytical process of the most extraordinary delicacy, and can by means of it easily make a qualitative analysis of a compound containing several elements. Thus Messrs. Bunsen and Kirchhoff have been enabled to exhibit the reactions of potassium, sodium, lithium, calcium, and strontium, in several mineral waters; to show the bands of sodium, potassium, lithium, and calcium in the ash of a cigar moistened with hydrochloric acid, and to point out differences in the composition of various limestones.

New Metals. But the greatest triumph of Bunsen's and Kirchhoff's new method of analysis, was the discovery of two new metallic elements, belonging to the group of alkali metals. While working on the residue of a mineral water from Kreuznach, in Germany, a spectrum was obtained which gave lines as simple and characteristic as those of lithium and sodium, but which were blue, and were not refera

1 The spectrum yielded by a flame containing the vapor of strontium is characterized by the absence of green lines. It contains, however, eight remarkable lines, namely, six red, one orange, and one blue. To examine the intensity of the reaction, Kirchhoff and Bunsen threw up into the air of the room, in the form of fine dust, 0.077 grm. of chloride of strontium, and thoroughly mixed the air by rapidly moving an umbrella; the lines immediately came out and indicated the presence of the six-hundred-thousandth part of a milligramme of strontium. The barium spectrum is distinguished by two very distinct green lines, by which the authors were enabled to detect with certainty one thousandth of a milligramme of metal. Calcium gives a very broad and characteristic green line, and, moreover, a bright orange line lying near the red end of the spectrum. Six tenmillionths of a milligramme of the chloride of this metal could be easily de

tected.

ble to any known element. The indefatigable experimenters, acting on the testimony thus obtained, evaporated down no less a quantity than twenty tons of the mineral water in question, and obtained from the residuum two hundred and forty grains of the platinum salt of a new metal which they have named CESIUM, from the Latin word casius, signifying grayish-blue, that being the tint of the two spectral lines which it shows. Further investigations showed the presence of cæsium in other mineral waters, and led to the detection of another element, which, from the circumstance of its yielding two very dark red spectral lines, has been termed RUBIDIUM, from the Latin rubidus, dark red. Both of these metals resemble potassium so closely that they cannot be distinguished from it by the usual re-agents, or before the blowpipe. Their presence in minute quantities can only be recognized by aid of the new method of spectral analysis. Properties of the new Metals.- Cæsium appears to be the constant companion of rubidium, and has thus far been found most abundant in the saline waters of Dürkheimer, in Germany. The atomic weight of cæsium is 123.4 (H=1): Symbol, Cs. It is the most electro-positive of all known elements.

Caustic cæsia resembles caustic potash; carbonate of cæsia is soluble in alcohol, in which reaction it differs from the carbonate of rubidia; sulphate of cæsia forms alum with the sulphate of alumina. Chloride of cæsium is deliquescent like the chloride of lithium.

Messrs. Bunsen and Kirchhoff have found traces of rubidium in almost all mineral waters; but it exists in greatest quantity in the mineral known as lepidolite; some of which, from Moravia, was found to contain about ths of its weight of the oxide of rubidium. The atomic weight of it is 85.36 (H=1): Symbol, Rb.

Caustic rubidia resembles caustic potash; carbonate of rubidia is insoluble in alcohol; it can be readily converted into bicarbonate. Nitrate of rubidia varies from nitrate of potassa in crystalline form. Sulphate of rubidia is isomorphous with sulphate of potassa, and forms cubic alum with the sulphate of alumina. Chloride of rubidium crystallizes in cubes.

Another new element, Thalium.—Mr. William Crookes, an English chemist, also announces the discovery, by means of the photo-chemical process of analysis, of another new element, belonging to the sulphur group, to which he gives the name Thalium - Gr. Θαλλος, green, from the circumstance of its yielding an intensely green spectral ray. Thus far the new element has been obtained in the form of a dense brown powder, from specimens of native sulphur. Its physical and chemical properties have not, however, as yet been described.

It is scarcely possible to overrate the probable importance to chemical science of this new and beautiful method of analysis. In fact, the discoveries of Bunsen and Kirchhoff seem to herald the birth of a new kind of terrestrial and stellar chemistry, inasmuch as it extends almost to infinity the limits within which the chemical characteristics of matter have hitherto been confined. "In spectral analyses," observe the discoverers of the process, "the colored bands are unaffected by any alteration of physical conditions, or by the presence of other bodies. The positions, therefore, which the lines occupy in the spectrum, indicate the existence of a chemical property as unalterable as

the combining weights themselves, and may accordingly be estimated with an almost astronomical precision."

New Instrument for Spectral Analyses. A new instrument for exhibiting the fixed lines in spectra, from different sources, far more simple than that made use of by Messrs. Bunsen and Kirchhoff, has been described by M. Mousson in Poggendorff's Annalen, under the name of the Spectroscope. The apparatus consists essentially of a tube blackened internally, and having at one extremity a plate of metal, with an adjustable slit for the admission of light. The prism is placed at the other extremity of the tube, so that the eye of the observer may be brought close to its second refracting surface. The tube is attached to an appropriate stand, so that it may be conveniently directed to the light to be examined; and the eye of the observer is protected from extraneous light by a small screen of metal attached to the tube. The edges of the slit must be ground perfectly true. This apparatus does not require a darkened chamber or delicate and difficult adjustments. In a communication to Silliman's Journal, July, 1861, Prof. Wolcott Gibbs states that it can be obtained in New York city of Mr. Chas. Sacher; price twenty-five dollars.

RESEARCHES BY MEANS OF THE PROCESS OF SPECTRUM ANALYSIS ON THE CONSTITUTION OF THE SOLAR ATMOSPHERE.

M. Kirchhoff, following up the line of investigation described in the foregoing article, has recently applied the process of photo-chemical analysis to the study of the constitution of the sun's luminous envelloping atmosphere. He maintains, as the result of examinations, that the sun has an ignited gascous atmosphere, which encloses a core of still higher temperature. If we could see the spectrum of this atmosphere, we should detect the bright lines which are characteristic of the metals existing in it, and should recognize the metals themselves from these. The more strongly luminous body of the sun does not, however, permit the spectrum of his atmosphere to appear. It inverts this spectrum; so that instead of the bright lines which the spectrum of the atmosphere alone would exhibit, dark ones make their appearance. We see, therefore, only the negative image of the spectrum of the sun's atmosphere.

In order to study the solar spectrum with the requisite degree of accuracy, Kirchhoff procured from the workshop of Steinheil an apparatus consisting essentially of four large flint-glass prisms and two telescopes.

With this apparatus the spectra are seen in a hitherto unattainable degree of distinctness and purity. It exhibits in the solar spectrum thousands of lines, with such clearness that they are easily distinguished from each other. It is the author's intention to draw the whole spectrum, as seen with his apparatus, and he has already done this for the portion which lies between Fraunhofer's lines D and F.

This apparatus exhibits the spectrum of an artificial source of light with the same distinctness as the solar spectrum, provided only that the intensity of the light is sufficient. A common gas-flame, in which a metallic compound evaporates, is usually not sufficiently luminous,