The Absorption Coefficient of Solution for Monochromatic Radiation. 21 



of water, for the curve shows that the alcohol becomes transparent 

 again at l,320jii/z, which would perhaps not be the case if water were 

 present even in small quantities, as pure water is quite opaque at this 

 point. Therefore it is believed that the maxima shown by this curve 

 are characteristic of the alcohol and not of any impurity. 



ETHYL ALCOHOL. 



The ethyl alcohol was refluxed and distilled repeatedly over lime. 

 Its density at 25 referred to water at 4 was 0.7851, which compares 

 favorably with the figure 0.78506 given by the Bureau of Standards, 

 Bulletin 19, page 7 (1916). 



PROPYL ALCOHOL. 



The propyl alcohol was refluxed and distilled once over lime. Its 

 density at 20 referred to water at 4 was 0.8037. The figure for the 

 anhydrous propyl alcohol given in Van Nostrand's Chemical Annual, 

 1913, page 312, is 0.80358. 



ISO-BUTYL ALCOHOL. 



The iso-butyl alcohol was refluxed and distilled twice over lime. Its 

 specific gravity at 20 referred to water at 20 was 0.8033. The figure 

 given by Biedermann, Chemiker Kalender, 1915, page 96, is 0.8031. 

 This alcohol showed signs of slight cloudiness hi the cell. The ab- 

 sorption curve also shows general slight absorption in the visible region 

 of wave-lengths. 



ISO-AMYL ALCOHOL. 



The iso-amyl alcohol was refluxed and distilled once over lime. Its 

 density at 20 referred to water at 4 was 0.8111. The figure given in 

 Van Nostrand's Chemical Annual, 1913, page 278, is 0.8104. 



DISCUSSION OF RESULTS WITH THE SOLVENTS. 



The absorption curves for water and the five alcohols have been 

 plotted together for the sake of comparison as shown in figure 3. All 

 the curves have a common axis of ordinates; the zero of the ordinate 

 axis is different for each curve, so that as a result each curve is trans- 

 posed a convenient distance above the neighboring curve. The 

 similarity in the positions of the maxima and minima of the curves 

 and the concordance in the values of a at these points are interesting. 

 Although the infra-red transmission of the alcohols has been studied 

 by a number of observers, 1 no determinations of the absorption coeffi- 

 cients in the region from 600/iju to 1,300^M have been recorded. The 

 absorption spectra of the above five alcohols and many other sub- 

 stances have been photographed by Abney and Festing. 2 In their 

 work the light was passed through a thickness of 3 inches or more of 



, Handbuch, vol. 3, p. 304. 2 Phil. Trans. 172, 887 (1881). 



