L 314 ] 



XLII. Intelligence and Miscellaneous Articles. 



ON DIFFUSION AND THE QUESTION, IS GLASS IMPERVIOUS TO GASES ? 

 BY G. QUINCKE. 



TT is usual to attribute to all bodies the property of porosity. 

 Respecting the magnitude of the pores or of the molecules of 

 which the bodies consist we know as good as nothing. It might, 

 however, well be possible that composite molecules, especially 

 those with greater molecular weight, occupy a greater space, and 

 constitute bodies with wider pores, than those whose molecular 

 weight is less. A hydrogen molecule would then occupy the 

 smallest space, and it would be conceivable that hydrogen particles 

 might pass through the pores of solid bodies like glass. 



Opposed as these views may appear to a now very prevalent 

 hypothesis concerning the nature of gases, the question can only 

 be decided by experiment. For this purpose, I have tried for years 

 to force hydrogen and carbonic acid, by pressures of from 40 to 

 120 atmospheres, through a glass wall of 1*5 millim. thickness, and 

 to determine, by the loss of weight, the quantity of gas that had 

 passed through. 



One leg of a Y-shaped glass tube was a capillary tube of 200 

 millims. length, closed above ; the other was a tube contracted in 

 the middle and open above, 150 millims. long, 8 millims. in 

 diameter, and its wall 1*5 millim. thick. Into the open leg a drop 

 of quicksilver was put ; upon this dilute sulphuric acid was poured ; 

 into the upper part some sheet zinc was pushed, which was kept 

 from contact with the acid by the contraction of the tube ; and 

 then the open end was carefully closed by fusion at a glass- 

 blower's lamp. Four tubes thus prepared underwent a double 

 weighing ; and then, by inclining the tubes, the sulphuric acid was 

 brought into contact with the zinc. 



The pressure of the hydrogen was shown by the diminution of 

 volume of the air in the capillary tube, which served for a mano- 

 meter. Its amount on the first day, in the different tubes, was 

 from 1| to 10 atmospheres, rose in five months up to 27-54 atmo- 

 spheres, and in 17 years up to 25-12Q atmospheres. During this 

 time the tubes were many times doubly weighed on an excellent 

 balance ; and exactly the same weight, within from 0*1 to 0'3 of a 

 milligram, was always found (8 -2556-1 6* 5461 grams). 

 ^ Another similar tube, with carbonate of lime and concentrated 

 sulphuric acid, in which the pressure of the carbonic acid gas 

 amounted on the first day to 21 atmospheres, after five months to 

 34 atmospheres, and after seventeen years to 44, showed likewise 

 always the same weight (14*6361 grams). 



Thus, according to these experiments, a pressure of from 40 to 

 100 atmospheres cannot, during a space of seventeen years, force 

 through 1*5 millim. thickness of glass a perceptible quantity of 

 carbonic acid. 



While at the commencement the concentrated sulphuric acid 

 wetted the glass sides of the tube, and showed a sharp marginal 

 angle (apparently 0°), gradually in the course of years the angle 



