CHAPTER V. 



INVESTIGATION WITH A ROCK-SALT PRISM. 



CivAss I : Methane: Derivatives. 



This class comprises all carbohydrates having an open chain, the so- 

 called " aliphatic compounds " as distinguished from the " cyclic " or 

 ring compounds 



Absorption Spectra op Gases. 



(Figs. 9 to 25 ; Tables I, V, and VII. )i 



Our knowledge of the absorption spectra of gases is confined to 

 the work of Angstrom,^ who studied CO, CO2, CH^, C2H^, and 

 (C2Hg)20. In fact, he is the pioneer in this subject. 



In studying gases the chief difficulty lies in obtaining them in a pure 

 state. The apparatus, including generator, purifiers, and gasometers, 

 must be air-tight, so that after the air has once been removed, none can 

 enter from outside. Fortunately, we have in liquid air a means for 

 obtaining small quantities of other gases in a more tangible state. By 

 combining fractional liquefaction and fractional distillation with the 

 usual chemical methods of purification one can obtain gases in a very 

 high state of purity, as will be noticed in the analyses of some of the 

 gases studied. In the present work the gases were first purified by 

 chemical methods. Several showed absorption bands in common, so 

 the work was repeated, using the additional method of liquefaction. 

 The way that the transmission curves have been changed and the 

 impurity bands have disappeared as a consequence will be noticed in 

 the several curves, especially ethane. 



The arrangement of the apparatus for generating and liquefying the 

 gases is shown in fig. 9, in which a is the generating flask, h is the wash- 

 ing tube, and c is the drying tube containing PoOs and cotton or glass 

 wool — the latter to present a large surface. This tube was always thor- 

 oughly cleaned before making a new gas. At d and e are the liquefac- 

 tion tubes, and g is the mercury gasometer, of 200 cc. capacity. The 

 operation consisted of fractionally liquefying the gas in d, and what 

 passed from d into e was liquefied there at a lower temperature. The 



^Tables I to VIII and figs. 12 to 132 are given at the end of the text. 



^Angstrom : Ofversigt af Kon. Vetensk. Akad. Forhandhgar, Stockholm, Nr. 7, 1890. 



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