180 



ANALYSIS OF GAS EVOLVED. 



is incessantly disturbing the constitution of the other, nor does this disturbance cease 

 until the contents of both jars are chemically the same. There are some beautiful ex- 

 periments of easy repetition which serve to show how rapidly gases and vapours can 

 thus percolate through fluids. Take a pint bottle, and pass through its cork, which 

 ought to fit it very loosely, a glass tube a foot long, drawn narrow at its upper end. Into 

 the bottle put a few drops of water of ammonia. Dip the wide end of the tube into a 

 solution of soap, and introduce it into the interior of the bottle, adjusting it in such a po- 

 sition by the cork, that when air is blown in at the narrow end, the soap-bubble which 

 expands at the wide end may occupy the middle of the bottle. Placing the lips on the 

 narrow end, blow a bubble an inch or more in diameter, and, without loss of time, cau- 

 tiously draw back again the air from the interior of the bubble into the mouth. A 

 strong ammoniacal taste is at once perceived. Now it is obvious that this ammonia 

 must have passed with very great rapidity through the bubble. 



796. A still more instructive experiment may be easily made. Take a three-ounce 

 bottle, with a wide neck, close the mouth of it by a film of soap-water, by passing the 

 moistened finger over it. Place it under a jar of protoxide of nitrogen. Instantly the 

 horizontality of the film is disturbed ; it swells upward, and is spontaneously expanded 

 by the passage of the gas through it into a bubble. The play of colour which attends 

 this experiment, and the excessive thinness which the film finally assumes, render this 

 one of the most beautiful experiments that chemistry can furnish ; for when the bubble 

 is almost invisible by reason of its incapacity to reflect light, and can only be seen in 

 particular positions, it still discharges its percolating function. 



797. This percolation of gases through liquids cannot be hindered by employing 

 oil, or such other liquids as botanical writers seem to imagine. Through common 

 lamp-oil, through copaiva balsam, Sic., hydrogen gas will escape with rapidity, and pro- 

 toxide of nitrogen and carbonic acid still faster. The law that regulates these phenom- 

 ena is a very simple one : the gas escapes through the confining medium with a rapidi- 

 ty proportioned to its solubility therein. 



798. These things being understood, it is obvious that when carbonic acid is de- 

 composed in the experiments we have been detailing, a variable portion of that gas will 

 intermingle with the oxygen collected. The proportions must be variable, for it de- 

 pends on the amount of carbonic acid remaining behind in the water, on the speed with 

 which the experiment is conducted, and other variable conditions. As before stated, 

 therefore, I shall leave out of consideration this carbonic acid, in discussing the analy- 

 sis of the collected gases, because it is present by accident, and is not essentially con- 

 nected with the phenomena, except in one instance, where dark heat is to be employed, 

 as will be described presently. 



ANALYSIS OF AIR EVOLVED FROM CARBONATED WATER BY THE SUN. 



799. I may remark, that this table contains a few out of a great number of experi- 



