476 Intelligence and Miscellaneous Articles. 



effect. A bichromate-of-potash battery of sixteen cells, with plates 

 of zinc and carbon twenty-five by six centimetres, was used. 



With a rectangle containing a larger number of coils of wire, 

 attached to a very delicate balance, by using a constantly acting 

 battery, the variation in the magnetism of the earth might thus be 

 advantageously observed. — Silliman's American Journal, May 1878. 



ON THE DIFFUSION OF CARBONIC ACID THROUGH WATER AND 

 ALCOHOL. BY PROF. STEFAN. 



When carbonic acid is parted from the atmospheric air by a 

 liquid cylinder, it diffuses through the liquid into the external space. 

 If the carbonic acid be kept under constant pressure, the rate of 

 diffusion will be constant ; the amount of carbonic acid issuing in 

 the unit of time will be to the cross section of the cylinder directly, 

 to its length inversely proportional. 



The density of the carbonic acid diminishes from the inner to 

 the outer boundary layer of the liquid which is saturated with the 

 acid. The quantity of carbonic acid passing in the unit of time 

 through the unit of the cross section is proportional to the fall in 

 the density. The proportionality factor is the coefficient of diffusion , 

 and can be determined from such observations. 



A second method for determining it consists in the observation 

 of the penetration of carbonic acid into a cylinder of liquid of great 

 length. The amount of gas which has entered into the liquid from 

 the commencement of the experiment up to a certain time is pro- 

 portional to the square root of this time. 



The velocities with which gases spread in liquids are of the same 

 order as those with which salts diffuse in their solvents. The 

 coefficient of diffusion of carbonic acid in water is nearly as great 

 as that of potassium chloride. The coefficient for the diffusion of 

 carbonic acid in alcohol is twice as great. 



Oxygen and nitrogen diffuse in both liquids more quickly than 

 carbonic acid ; but the highest velocity of diffusion belongs to 

 hydrogen gas. The peculiarities by which the gases are characte- 

 rized in reference to their molecular motion in the free state, and 

 which come out especially in their diffusion through porous solids, 

 they still possess in the interior of liquids by which they have been 

 absorbed. 



That reciprocal action between gases and liquids, in consequence 

 of which different gases are absorbed in different measure by one 

 and the same liquid, has no influence upon the velocity of the 

 diffusion-motion ; the greater or less capacity of absorption of the 

 gas determines in each given case the density of the diffusion- 

 current only. — Kaiserliche Akademie cler Wissenschaften in Wien, 

 maihematiscli-naturwissenschaftliche Classe, March 21, 1878. 



