260 SCIENTIFIC AMUSEMENTS. 



reason for this is that the kind of electrification here in question 

 only affects the outer surfaces ; and the inner bubble is consequently 

 entirely unaffected, as to all intents and purposes it is an internal 

 object protected against electrical influences by the outer coating 

 of the larger bubble. The most delicate electrical indicators 

 exhibit no sign of electrification when they are similarly situated, 

 i.e., when they are completely enclosed in some conducting outer 

 coating. 



Expt. 307. Soap Bubble Balloons. Provide a bladder, into the 

 neck of which a piece of ordinary ^ inch brass gas piping is fixed 

 air tight, a tap being attached to the piping (Expt. 177). By 

 means of a piece of india-rubber tubing the bladder may be con- 

 nected with the burner of an ordinary gas jet, all air having been 

 first squeezed out of the bladder ; on opening the taps the bladder 

 will become slowly inflated with coal gas. If the bladder thus 

 filled be held under the arm and gently squeezed, the coal gas will 

 be forced out of it when the tap is opened ; by means of the india- 

 rubber tubing the blowing tube can thus be supplied with coal gas 

 instead of air from the lungs. If you then blow a bubble filled 

 with coal gas and detach it by a shake from the blowing tube, you 

 will see that it ascends up to the ceiling more quickly than a 

 bubble simply filled with the breath ; this is because, whilst 

 slightly warm air is lighter than cooler air, bulk for bulk, coal gas 

 is lighter still, and is therefore more buoyant when used to fill a 

 bubble or balloon. 



Provide a light wire ring with three threads attached to it at 



equal intervals (fig. 113); moisten 

 the ring with soap solution, blow 

 a coal gas bubble and make it 

 adhere to the ring, and detach 

 the blowing tube by a shake ; if 

 the ring is not too heavy, the 

 bubble will be light enough to 

 lift its weight and a small paper 

 disc or car attached to the threads, 

 thus forming an actual miniature 

 balloon. A light thread attached 

 to the car then converts the whole 

 into a "captive balloon," which 

 can be allowed to ascend or pulled 

 Fig. 113. Soap Bubble Balloon down again by the thread at will, 

 with attached Car. After gome time the gag escapes 



through the wall of the soap bubble by osmosis, and air more 

 or less completely takes its place (vide Expt. 79); so that the 



