28 



ACTION OF TERNARY ARRANGEMENTS. 



its own parts, dense fumes of muriate of ammonia make their appearance, which continue 

 until the substance of the bubble has entirely returned into the tube. The extraordinary 

 rapidity of this action is remarkable. The bubble is scarcely blown before it is full of 

 ammonia ; and it is not less interesting to observe how the colours play with change 

 of atmosphere. A little cylinder expanded to the size of a pea, which, in common 

 air, is opaque white, and which would not be coloured until expanded to six or eight 

 times that diameter, becomes deeply tinged as soon as it is penetrated by ammonia. 

 If restored to the free atmosphere it loses all its beauty, and these alterations may be 

 kept up at pleasure by merely changing it from one medium to another. 



81. When, for the purpose of experiment, it is desirable to have a permanent bub- 

 ble, a small column of moisture from the tongue must be allowed to close the capillary 

 termination of the tube. 



82. In the same manner, hydrosulphate of ammonia is found to pass with instanta- 

 neous rapidity through the film, and may be detected by a paper dipped in acetate 

 of lead. The colours in this case become very quickly stable, as with ammonia, and 

 do not produce that iridescent play which the passage of certain other substances 

 affords. It is, however, essential to the success of these experiments that the sub- 

 stances about to be passed through the film shall not have any chemical action upon it. 

 Thus, it is not possible to use muriatic acid, which decomposes soap, but there is no 

 difficulty in the management of such as oxygen, hydrogen, nitrogen, &c. The passage 

 of hydrogen through these films is exemplified in the following table : 



Diameter of a bubble of hydrogen gas exposed, to atmospheric air. Diameter of a bubble of atmospheric air exposed to hydrogen gat 



83. The third column, marked *, in these tables was taken when the black spot on 

 the top of the bubble was about half an inch in diameter ; for, as the coloured rings 

 were the same in each experiment, and the surface incapable of reflecting light of equal 

 extent, it is to be presumed that the measures were obtained under like circumstances, 

 as far as the thickness of the film was concerned. In all cases the bubbles were blown 

 by pressure on a gum elastic bag. This method of measuring the expansion, though 

 suitable for general purposes, cannot, however, be extensively relied on, owing to thermal 

 disturbance and the earth's action changing the figure from a true sphere to a prolate 

 spheroid. 



84. It is interesting to remark with what extraordinary rapidity these permeations 

 take place. If we expand a small bubble in a vessel of ammonia, hydrogen, sulphuretted 

 hydrogen, &c., by means of the mouth, and, without removing the lips from the capillary 

 opening of the tube, inhale immediately the contents of the bubble, the gaseous matter 

 will impress the organs of taste with a very distinct savour, peculiar to the gas on which 

 the experiment is tried. There is a class of vapours which appears to possess little 

 or no affinity for water, such as ether and the essential oils ; these, however, percolate 

 through tissues of water with rapidity. On covering the bottom of a vial with oil of pep- 



