On the Condensation of Gases by, Smooth Surfaces, 335 



already found for sulphurous acid could not be made the basis 

 of comparison. We must be sure that the gas made use of was 

 perfectly pure. Hence the coefficient of expansion was always 

 determined with the two surfaces simultaneously, making use of 

 two such instruments as that described in the memoir above 

 alluded to*. The tubes for both were filled at the same time, 

 by conducting the gas first through one and afterwards through 

 the other. 



The calculation of the coefficients of expansion is carried out 

 exactly as in the above memoir ; and as the glass is of the same 

 kind as that formerly used, the same coefficient of expansion for 

 the glass is taken. 



The calculation gave for the coefficient of expansion of the 

 sulphurous acid from 0° to 100° C. 



In the tube. 

 * Without the rods. With the rods. 



0-3822. 0-3896. 



These numbers prove that a condensation has taken place upon 

 the surface of the glass. In order to calculate the magnitude of 



the condensation, let - denote the volume of gas at 0° condensed 

 n ° 



on the surface of the rods, and let the volume of the uncon- 



densed gas, or at least condensed only on the sides of the large 



tube, be = 1, then we have 



(l+ ^)l*3822 = l-3896, 

 from which we obtain 



- =0-00535. 



n 



As, however, the diameter of the tube amounted to 20 milli- 

 metres and its length to 250 millimetres, the tube which con- 

 tained no rods had a content of 78525 cubic millimetres. 

 Further, as each rod had a diameter of 1 millimetre and a length 

 of 250, that is, a volume of 196*31 cubic millimetres, the volume 

 of the 250 rods amounted to 49078 cubic millimetres. Hence 

 the volume of the air contained in the tube with the rods was 



78525-49078 = 29447 cubic millimetres. 



The gas condensed on the surface of the glass rods was 

 therefore 



000535 .29447=157-5 cubic millimetres. 



The surface of the rods amounted to 196704 square milli- 



* In den Abhandlungen der K. Akad.fur 1841, p. 72. See Pogg. Ann. 

 vol. lv. p. 10. 



