88 A SYSTEM OE PHYSICAL CHEMISTRY grounds — that the water molecule possesses two main moments of inertia, which are in the ratio of i : 2. Eucken finds, on taking two values for I, one of which is approximately twice the other, and calculating the corresponding series as given by the Bjerrum expression, that satisfactory agreement is obtained between the calculated and observed band maxima. The following table contains Eucken's results :— Inkra-Red Absorption Bands of Water Vapour. A Observed (in (i).
ABSORPTION SPECTRUM OF HYDROGEN CHLORIDE 89 The first column contains the value of «, i.e. the order of that maximum reckoned from the middle of the absorption band. The middle of the 37/z 3 B/i. 3-5//, 3-4/fc 3-3// 3-2/* Fig. g.— Hydrogen chloride gas (E. von Bahr). S denotes slit width. Dotted curve due to Burmeister. Upper full curve corresponds to lower full curve corresponds to 380 mm. 760 mm. ; absorption band is characterised by the wave-length Xq = 3'474M> ^"d the frequency vq = 8 "63 6 x lo^^. «. Hydrogen Chloride Gas.