1909.] Elasticity of Rubber Balloons and Hollow Viscera. 491 



deflated, provided that the elastic limit is not approached too closely, the 

 nearer does the inflation pressure gradient approach the deflation. We 

 may regard this as due to the partial removal of the disturbing initial 

 rigidity. 



4. If a balloon be inflated until the pressure, after the usual crest, falls 

 and tends to remain constant, and be kept inflated for some time, say 

 24 hours, and then be rapidly deflated and once more inflated in measured 

 increments, the graph displays no crest and may be a true hyperbolic curve. 

 The following experiment illustrates this important fact : — 



A balloon was inflated until the pressure ceased falling, and was kept 

 inflated in the thermostat for 24 hours. It was then rapidly deflated and 

 the usual inflation by the burette commenced. On plotting pressure against 

 radius (fig. 5), I was struck by the regularity of the graph, and recollecting 

 that a balloon of perfect elasticity would give a rectangular hyperbola, 



E 



O- 



250 













2O0 

 I50 

 IOO 























50 

 O 























1 2 3 4 5 6 



Radius in centimeters. 



Fig. 5. 



proceeded to ascertain if such were the case here. If this were a rectangula 

 hyperbola, the asymptotes being parallel to the co-ordinate axes, it ought to 

 satisfy the equation (r — a) (p — b) = c. 



To calculate a and b I used the ordinary three-point method. The value 

 for a was found to be 2-8, that of b 287"8. 



From radius =3-29 to radius =4-37 the product (r—a)(b — y) is a 

 constant. To illustrate this graphically we can plot b—y against the 

 reciprocal of r—a, and should obtain a straight line passing through the 

 origin. This is shown in fig. 6. 



