Spectroscope direct vision

Vertical Displacement of Ellipses.— In the diagram figure 1, M and N are half silvered, M and N opaque mirrors C and C the U tube referred to in the preceding note and here to be removed. L is the collimated beam of white light and G T the direct vision spectroscope. 

A smaller, relatively inexpensive, and more compact instrument, which is more useful for routine tests in qualitative analysis, is the direct vision spectroscope with comparison prism, shown in Fig. II.4. 

The sodium flame masks that of other elements, e.g, that of potassium. Mixtures can be readily detected with the direct vision spectroscope (see Fig. II.4). A less delicate method is to view the flame through two thicknesses of cobalt blue glass, whereby the yellow colour due to sodium is masked or absorbed, and the other colours are modified as listed in Table V.3. 

Yttrium is one of the most abundant rare earth elements and its purification is easily accomplished. Yttrium fractions from a bromate series are freed from dysprosium, holmium, and erbium by fractional precipitation with ammonia, K2OO4, or NaNC>2. The latter is probably the most effective. Yttrium salts give no absorption lines ini the viable portion of the spectrum, consequently the removal of holmium and erbium is easily observed by the direct vision spectroscope. 

In direct vision spectroscopes a compound prism is used, so made up of prisms of different kinds of glass that the emerging ray is nearly in the same straight line as the entering ray. 

The micro-spectroscope (Fig. 18) is a direct vision spectroscope used as the eye-piece of a microscope. With it the spectra of very small bodies may be observed. 

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