EXPERIMENTS WITH SOAP BUBBLES BOYS. 213 



If tho pii)e is warmed a little, the bubl)le whicli will then contain 

 slightly warmed air will be a genuine Montgolfier's balloon, and will 

 rise by its ascensional force. If the bubble have a diameter of 1 foot, 

 it is surprising how long it wUl remain sufllciently warm to float in the 

 air. When it begins to descend, it can be stopped by means of a 

 current of air directed upward either by blowing ^vith the pipe or 

 with a pair of bellows. In the latter case, by accommodating the 

 movements of the bellows to the soap bubble's natural period of 

 oscillation, we may at once keep it in the air and cause it to execute 

 vibrations of great amplitude. We may form it again and blow into 

 the interior a very little illuminating gas, and it will then float of 

 itself. The very heat of our breath suffices to make a bubble ascend 

 if it be sufficiently large, e. g., 6 inches m diameter. The tin funnel 

 of the old-fashioned gazogene is all that is needed for this experiment. 

 But with a heated pipe, we may make even very small bubbles 

 ascend for a few moments. The most convenient method of warming, 

 however, is to aUow the warm gases above a candle flame to be drawn 

 in by the injector for a few seconds. Bubbles so blown will rise above 

 buildings and float away out of sight. 



It is clear that a cold bubble blown with air will float upon carbonic 

 acid. I once entered the Grotto del Cane, near Naples, and blew 

 numerous bubbles which floated all about me in the heavy gas, to the 

 great delight of the custodian. Vapor of ether is more easily prepared 

 and is still heavier than carbonic-acid gas. It is easier to use it for 

 the purpose of supporting a bubble fflled with air, but the vapor 

 soon condenses upon the bubble, evaporates in the interior, and at 

 the end of a short time the latter sinks into the vapor. If it be 

 caught on a ring and brought near a lighted candle, the bubble will 

 burst into flame, thus showing that the vapor has penetrated the 

 interior. We may again blow a bubble by means of the tin funnel 

 and hold it in the vapor. If we then bring a lighted candle near the 

 open end of the funnel, a long flame like that of a Bunsen burner is 

 formed by the issumg vapor. It is interesting to observe that if 

 benzene (CgHe) be substituted for ether, the bubble will float as weU 

 but the penetration of the vaj)or will be less rapid. However, it 

 finally enters and the bubble then burns with a brilliant flame. 

 With pentane (C5H12), on the contrary, the bubble floats without the 

 penetration of vapor, this substance being practically insoluble. A 

 bubble of oxygen floating upon ether or benzene explodes \dolently 

 like a bomb, when ignited. 



The vapor of ether and a few other liquids somewhat diminish the 

 superficial tension of a soap bubble, while the greater number of 

 organic vapors increase it. This is especially noticeable with ammo- 

 nia, which undoubtedly acts chemically upon tho free molecules of 

 oleic acid, combines with them and still further neutralizes the 

 85360°— SM 1912 15 



