486 Prof. W. A. Osborne and Mr. W. Sutherland. [July 5, 



Methods. 



The balloons were of the common variety sold as children's toys, and were 

 of varying sizes. A balloon was firmly tied to a glass capillary cannula and 

 held vertically in a glass flask which was immersed up to the neck in an 

 Ostwald thermostat (fig. 1). The temperature of the latter was kept (with 

 a maximum variation of o- l C.) at 35°"5 C. The glass cannula was 

 connected by means of fine-bore pressure-tubing to one limb of a capillary 

 T-piece, a second limb of which led to a water manometer, whilst the third 



limb was connected with a burette for 

 admitting measured volumes of air. The 

 connecting tubes were made as short and 

 of as narrow bore as possible so that the 

 contained volume of air could be neglected 

 in calculation. The burette at its lower 

 end was connected with a levelling tube 

 containing mercury, and at its upper end 

 had a three-way tap. In one position of 

 the tap a sample of air of definite volume 

 and at atmospheric pressure could be taken 

 from the outside air; on the tap being 

 turned this air could be driven through the 

 connecting tubes into the balloon, the 

 mercury being accurately brought to the 

 beginning of the bore of the tap. Con- 

 versely, the balloon could be deflated in 

 measured decrements by the same burette. 

 The water manometer consisted of a straight 

 glass tube of 3 mm. bore firmly tied to a 

 vertical scale, and connected at its base 

 with a shorter vertical tube on which was 

 a mark. By means of a three-way tap, 

 capable of connecting the manometer either 

 with the outside air or with an elevated reservoir of water, the level of the 

 water in the shorter limb could be brought to its mark, allowing direct 

 readings to be made from the scale as well as preventing change in the 

 volume of the tube system. 



The radius of the balloon was calculated from the volume of the air 

 admitted by the usual formula. This involved two assumptions, first that 

 the balloon was spherical, and secondly, that the volume of the enclosed air 



