M. Deville on Diffusion through Iron Tubes. 231 



the annular space ; heat was applied, and kept pretty constant. 

 This is indicated by the manometer, which ought not to vary 

 appreciably when the stopcock, by which the nitrogen enters the 

 iron tube, is closed. At this moment (the nitrogen-stopcock 

 being closed) a current of hydrogen was passed into the annular 

 space. It was thus seen that, in proportion as hydrogen displaced 

 nitrogen in the annular space, the mercury ascended in the 

 manometer and attained such a level as to indicate that the 

 internal pressure had been more than doubled. This is pure 

 hydrogen, which, penetrating the sides of the iron tube, adds its 

 pressure to that of the nitrogen, which does not escape in any 

 appreciable quantity. 



After some hours the pressure attains a maximum ; the pres- 

 sure could be calculated from the height of the mercury iu the 

 manometer; the three-way stopcock was then worked so as to 

 allow the gas in the interior of the tube to be collected and ana- 

 lyzed. Thus there were all the elements for obtaining the pressure 

 of each gas in the inside of the iron tube. Throughout the ex- 

 periments a constant current of hydrogen traversed the annular 

 space. 



After this first experiment, one or more may be made by 

 placing in its original position the three-way cock, which simply 

 places the iron tube in communication with the manometer (the 

 nitrogen stopcock is not touched, and thus new quantities of gas 

 are not introduced). This second heating gives rise to a new 

 maximum pressure, less, however, than the first. And in the 

 same way a third and fourth experiment may be made. 



M. Deville then gives a tabular statement of his results, from 

 which he draws the following conclusions. 



"Hydrogen passing into the annular space at the atmospheric 

 pressure tends to enter the iron tube by traversing its pores. 

 (1) At a temperature but little elevated, hydrogen has both in- 

 side and outside the iron tube exactly the same pressure (that of 

 the atmosphere) as if there were no nitrogen in the interior. 

 Hence the law of the diffusion of gases, whether into liquid or into 

 gases themselves, is verified. (2) If the temperature is very high, 

 the pressure of hydrogen in the iron tube is much higher than 

 the pressure in the exterior. These results are in complete 

 contradiction with all facts known regarding the diffusion of 

 gases. 



" The only two circumstances which might serve for their ex- 

 planation are as follows : — 



"1. In the inside of the tube a mixture of nitrogen and hydro- 

 gen acts like a homogeneous substance, drawing to itself pure 

 hydrogen from the outside as if part of the physical properties 

 of the hydrogen were destroyed by the presence of the nitrogen. 



