Prism Bunsen

Monochromators (a) Czerny-Turner grating monochromator, (b) Bunsen prism monochromator. 

FIGURE 7-18 Two types of monochromators, (a) Czerney-Tumer grating monochromator and (b) Bunsen prism rnonochromalor. (In bolh instances, a, > Ac.)... 

Many elements are present in the earth s crust in such minute amounts that they could never have been discovered by ordinary methods of mineral analysis. In 1859, however, Kirchhoff and Bunsen invented the spectroscope, an optical instrument consisting of a collimator, or metal tube fitted at one end with a lens and closed at the other except for a slit, at the focus of the lens, to admit light from the incandescent substance to be examined, a turntable containing a prism mounted to receive and separate the parallel rays from the lens and a telescope to observe the spectrum produced by the prism. With this instrument they soon discovered two new metals, cesium and rubidium, which they classified with sodium and potassium, which had been previously discovered by Davy, and lithium, which was added to the list of elements by Arfwedson. The spectroscopic discovery of thallium by Sir William Crookes and its prompt confirmation by C.-A. Lamy soon followed. In 1863 F. Reich and H. T. Richter of the Freiberg School of Mines discovered a very rare element in zmc blende, and named it indium because of its brilliant line in the indigo region of the spectrum. 

T. Melville noted in 1752 that sodium colours the flame of alcohol yellow, and A. S. Marggraf used this as a test to distinguish sodium from potassium salts. With an ordinary one-prism spectroscope, the spectrum appears with a single yellow fine corresponding with the D-line of the solar spectrum. This line really consists of two lines of wave-length 5896 and 5890. The emission spectrum of sodium shows many other lines of feeble intensity. In a salted Bunsen s flame, practically... 

Robert Bunsen and Gustav Kirchhoff, whom we encountered in passing in the previous chapter, took a major step in this direction in the middle of the nineteenth century. Bunsen moved to Heidelberg in 1852, and there he worked on combustion. Kirchhoff joined Bunsen two years later. It was Kirchhoff the physicist who suggested to Bunsen the chemist that a prism would be useful to examine the color of flames as they were affected by different metallic salts. 

The righthand illustration shows the simple and elegant construction of Bunsen and Kirchhoff s first form of spectroscope. A prism is supported within a box (A). 

Potassium salts impart a violet coloration to the Bunsen flame, the tint appearing reddish-violet through an indigo-prism or blue glass. 

Spectroscope A laboratory instrument invented by Robert Bunsen and Gustav Kirchhoff in 1859. Using a colorless flame, the spectroscope first heats a sample of matter until it releases light. The light is passed through a prism to produce a spectrum. Each element has a unique set of spectral colors, so the device can be used to identify elements and elements in compounds. The spectroscope was also used to identify a number of previously unknown elements, such as helium. The spectroscope is still used today, and astronomical spectroscopes are used to identify stars and even to tell their age. Temperature A measurement of the heat energy in a substance. There are three main temperature scales used in the world Celsius, Fahrenheit, and Absolute (also called the Kelvin scale). 

Figure 24F-2 Bunsen burner of the type used in early spectroscopic studies with a prism spectroscope of the type used by Kirchhoff. (From H. Kayser, Handhuch der Spectroscopic. Stuttgart, Germany S. Hirzel Verlag GmbH Co., 1900.)...

Figure 25-6 Types of monochromators (a) grating monochromator (b) prism monochromator. The monochromator design in (a) is a Czemy-Turaer design, while the prism monochromator in (b) is a Bunsen design. In both cases,...

Atomic spectroscopy is the oldest instrumental elemental analysis principle, the origins of which go back to the work of Bunsen and Kirchhoff in the mid-19th century [1], Their work showed how the optical radiation emitted from flames is characteristic of the elements present in the flame gases or introduced into the burning flame by various means. It had also already been observed that the intensities of the element-specific features in the spectra, namely the atomic spectral lines, changed with the amount of elemental species present. Thus the basis for both qualitative and quantitative analysis with atomic emission spectrometry was discovered. These discoveries were made possible by the availability of dispersing media such as prisms, which allowed the radiation to be spectrally resolved and the line spectra of the elements to be produced. 

Discussion When gases are heated to a sufficiently high temperature they emit colored light. The Bunsen flame is hot enough to volatilize the alkaline metals and alkaline earths and some of their compounds and thus to impart characteristic colors to the flame. All compounds of a given metal produce the same color, so that the appearance of the flame serves as a delicate test for that metal. Since the chlorides are the most volatile compounds, the material to be tested is usually treated with hydrochloric acid before it is put in the flame. The flame may be observed directly, or observed through a prism, which spreads out the light into separate colored bands. 

As shown in Figure 7-2()b. the .iurowprism, which permits more compact monochromaior designs, is a 30 prism with a mirrored hack. Refraciii>ii in this typo of prism takes place twice at the same interface so that the perU)rmance characierisiics are similar to those of a bi) prism in a Bunsen mount. 

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