66 The Microscope. 



remotest part of any large hall will set afloat a current charged with 

 sodium chloride, which is present everywhere, and cause a flash in 

 every flame that lights such hall, and this yellow flash will yield 

 the sodium spectrum, and thus reveal the presence of this metal." 



This sensitiveness of reaction is not confined to the sodium 

 chloride alone. The y^j^inr milligramme of chloride of barium gives 

 a very distinct reaction. Lithium reacts with the greatest prompt- 

 ness to the Yoooo^o¥ P^^^ °^ ^ milligramme; strontium to ytttAtoo of 

 a milligramme; caesium to the ooJ^^Tr part of a milligramme. 

 Thallum, arsenicum, plumbum, antimonium and nickel, and many 

 others, respond to very minute quantities of material also; we have 

 already spoken of the intense sensibility of rubidum. 



ABILITY OF THE SPECTROSCOPE TO ANALYZE SOLIDS, FLUIDS AND GASES. 



Whenever it is desirable to examiie solids, we must bring them 

 into a state of an incandescent, vaporous condition by heat. Some 

 metals and their salts can be examined by means of the Bunsen 

 burner. When a higher temperature is required, we may resort to 

 the electric arc, which is capable of fusing every metal known. 

 W^hen the vapors of metals and minerals are thus examined spectro- 

 scopically, we observe bright lines in various parts of the spectral 

 field. We give a few examples in the subjoined diagram. One 

 bright line coincident with the D line, is the sodium line. The 

 single line near E, lying in green, is characteristic of thallium. 

 The two bright lines between E and C, also in green, are peculiar to 

 silver. The spectrum No. 10 is produced from a hydrochloric solu- 

 tion of the ash of the human body. (Thudicum). The spectral 

 field shows many red, yellow, green and blue lines in various parts 

 of a dark field. By careful measurement it is found that these 

 lines are peculiar to six metals — potassium, sodium, lithium, 

 rubidum, caesium and calcium. Magnesium and iron, always 

 present in the ash, are not represented in this spectrum, requiring 

 the heat of an electric arc to make them visible. 



In order to examine fluids we place them before the slit of the 

 spectroscope in suitable glass tubes, or vessels with piano-parallel 

 walls. When light is made to pass through these fluids ere it 

 impinges upon the prism, we witness an absorption in various parts 

 of the spectrum, varying, of course, with the fluids employed; 

 these dark bands are called absorption bands. Some colored fluids 

 give one or more bands, as may be seen on the diagram. These 

 bands are changing in position, depth of shading, distinctness of 

 tline, breadth, and manner of appearance, furnishing in this way 



