MOISTURE COXDEXSATIOX ON CLASS WOOL 195 



A CURVE OF MOISTURE COXDEXSATIOX ON GLASS 



WOOL. 



L. E. DODD. 



Experimental results of Professor F. T. Trouton 1 relating to 

 equilibrium vapor pressure and total mass of water vapor fed 

 to glass wool that had previously been thoroughly dried, showed 

 an interesting drop in the curve at about half saturation pres- 

 sure. The character of the curve appeared to afford grounds 

 for a theory, proposed by Trouton, which supposed the con- 

 densation to have taken place in two modes, or states, which he 

 called the alpha and the beta states. After thorough drying, 

 employing the three agencies of continued vacuum, phosphorus 

 pentoxide, and a temperature of about 160°, moisture in the 

 alpha state was supposed to condense on the dried surface first. 

 The alpha condensation required relatively only a small amount 

 of water. With the equilibrium pressure at about half the 

 saturation value, which followed after but two or three feeds, 

 and with additional water fed to the glass wool, the equilibrium 

 pressure dropped, at which time the beta condensation was sup- 

 posed to have begun, following a condition of supersaturation. 

 The alpha condensation was interpreted as forming a nucleus 

 for the beta type. After a few more feeds the curve rose again 

 toward saturation. Trouton took the view that his results were 

 theoretically to be expected from the shape of curve given by a 

 characteristic gas equation, and that the same results could be 

 expected from surfaces in general that had been in like manner 

 thoroughly dried. More recent work by Mohr 2 and by Gossrau 3 

 has, however, thrown doubt on the supposition that Trouton 's 

 results are simply a response to the demands of the characteristic 

 gas equation. These investigators found that the Trouton ef- 

 fect, i. e., the drop in the pressure-mass curve, was present only 

 in the case of alkali glasses. 



With Trouton 's theory in view, before the work of Mohr and 

 of Gossrau had become known, and in view also of experimental 



Crouton, F. T., Proc. Roy. Soc, Ser. A, 79, July 10, 1907. p. 383. 

 -Mohr, Erich: "Ueber Adsorption uml [Condensation von Wasserdampf an 

 blanken Glasflachen," Inaug. Dissert., Halle. 1911. 



3 Gossrau, Gotthard : "Untersuchungen uber Adsorption von Wasserdampf 

 an blanken Glasflachen," Inaug. Dissert., Halle, 1913. 



