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L. On the Condensation of Gases by Smooth Surfaces. 

 By Professor Magnus*. 



IN a discourse given in 1845, on the occasion of my becoming 

 ordinary professor, I communicated the results of certain 

 experiments, which, although not without interest, I thought it 

 well to defer publishing until time should enable me to render 

 them more complete. I find, however, in the Comptes Rendus 

 of the 6th of June of the present year, a note by MM. Jamin 

 and Bertrand wherein a similar subject is treated in a different 

 manner. This induces me to lay the results of my experiments, 

 although they are still incomplete, before the Academy ; partly 

 because they furnish a corroboration of the observations of 

 MM. Jamin and Bertrand, but more particularly because the 

 method I have adopted permits not only of establishing the fact 

 of condensation, but also to measure the amount of it as referred 

 to the unit of surface. 



After having found that different gases expand differently, 

 and M. Regnault, retracting his first communication, having 

 obtained values almost identical with mine, no doubt could exist 

 as to the accuracy of the different coefficients of expansion. It 

 appeared, however, of interest to examine whether the gases were 

 condensed upon the interior surfaces of the glass vessels made 

 use of, and whether such a condensation exerted any influence 

 on the determination of the coefficient of expansion. 



The coefficient was therefore determined by first bringing the 

 gas into contact with a certain surface, and afterwards allowing 

 a larger surface in comparison to its volume to act upon it. In 

 the first case a glass tube was made use of, possessing a diameter 

 of 20 millimetres and a length of 250 millimetres ; in the second 

 case a tube of the same dimensions, but within which 250 glass 

 rods were placed, of the same length as the tube and of 1 milli- 

 metre diameter. The surfaces of the glass in the two tubes were 

 therefore nearly in the ratio of 1 : 13*5 ; the volume of air in the 

 latter being less than that in the former by the space taken up 

 by the glass rods ; so that, referred to the quantities of gas, the 

 surfaces were nearly in the ratio of 1 : 36. 



The determination was effected in the same manner as in the 

 case of the expansion of gases f. Assuming that the condensa- 

 tion would be greatest in the case of those gases which were 

 nearest to their point of condensation, the first gas operated on 

 was sulphurous acid. In the determination of such small values 

 as here come under consideration, the coefficient of expansion 



* From the Monats Bericht der Akademie der Wissenschaften zu Berlin. 

 t Abhandl. der K. Akad. der Wissensch. fur 1841, p. 59; Pogg. Ann. 

 vol. lv. p. 10. 



