36 Henry H. Dixou. 



subsequent exposure to air this water was allowed to become saturated 

 with dissolved air. During exposure care was taken to shield the watei- 

 from dust, which might not have been completely wetted or which 

 might have introduced small bubbles. To fill the vessel a small 

 quantity of water in it was raised to ebullition, and, while steam was 

 issuing- from the attenuated tubulure, the latter was submerged in the 

 dust-free water. As the steam witliin condensed and the vessel cooled 

 the latter became completely filled with water. A small bubble was 

 then introduced and the vessel was closed by sealing off the tubulure. 



If the vessel was then cautiously heated, the water expanded 

 more than its glass envelope and the air bubble was compressed. 

 The bubble became smaller and smaller as the temperature rose and 

 the contained gas was forced into solution. When the bubble had 

 readied very small dimensions and was about to disappear great care 

 had to be exercised in the further application of heat; for if the 

 water expanded too much and strained the glass beyond its elastic 

 limit, the whole experiment was rendered abortive by the breaking 

 of the glass. But. if the heating process had been carried on success- 

 fully and all the air had been dissolved so that the water had been 

 made to completely fill the vessel without breaking it, heating was 

 stopped and the water ceased to expand. 



At this moment the water in the vessel was either in compression 

 being constrained by a tension in the glass-walls, or it was quite 

 unconstrained, just exactly filling the envelope, and neither suftering 

 compression nor causing tension in the walls. As soon as cooling 

 began, the water and the glass commenced to contract. The coefficient 

 of expansion for heat of water being greater than that of glass, the 

 water tended to contract more. This contraction however was resisted 

 by its adhesion to the glass and its own cohesion, and consequently 

 a stress or tension, which kept it sufficiently dilated to fill the glass 

 was set up. As cooling proceeded the tension grew greater and greater, 

 till at last either tlie adhesion or cohesion was overcome and a break 

 appeared either between the water and the glass or in the substance 

 of the water itself. The appearance of this rupture was signalised by 

 a sharp click, and a bubble sprang into existence in the water. The 

 bubble thus produced rapidly augmented in size as the water, now 

 relieved from the stretching forces assumed a volume corresponding 

 to its temperature at the moment. Bubbles appear round the original 

 bubble and pass into it. 



By estimating the amount of deformation ^) of the glass envelope 

 when strained by the contracting water, and by determining experi- 



^) H. H. Dixon and J. Joly, On the Ascent of Sap. Phil. Trans. Roy. See. 

 London, Vol. 186, (1895), B, p. 569. 



