in vacuo and in Gases. 275 



of density continues, whatever volume the bubble may acquire in 

 rising through the liquid ; for I have ascertained that the tem- 

 perature of the vapour is the same, whether the solution boil 

 quickly or slowly, and that it is also the same when the liquid 

 rises to a great height above the heated bottom, although in this 

 latter case the bubbles often acquire a very considerable volume 

 before bursting at the surface of the liquid. 



On the other hand, in order to explain the great diminution 

 of temperature undergone by the vapour at the moment of its 

 escape from a boiling solution strongly impregnated with certain 

 salts, admitting the results which I have obtained as to the 

 quantity of heat which becomes latent by the expansion of elastic 

 fluids, we must suppose that the bubble of vapour whilst still in 

 the midst of the fluid, experiences a very considerable excess of 

 compression, much greater, indeed, than can reasonably be 

 admitted. 



I have, however, instituted some experiments with a view to 

 ascertain whether the fact proved by Eudberg arises from a 

 general law, such as that enunciated by him, or whether it must 

 be attributed simply to the circumstances under which his expe- 

 riments were made. 



I first of all wished to ascertain whether this phsenomenon is 

 presented with the same constancy when saline solutions are 

 boiled under pressures very different from the ordinary atmo- 

 spheric pressure, for all Rudberg's experiments were made under 

 the latter. I made use of the small copper boiler in which I 

 made my former determinations of the elastic force of the vapour 

 of water {Mem. de VAcad. vol. xxi. p. 515). The lid of this 

 boiler is traversed by four tubes hermetically closed at their 

 lower extremities ; two of these tubes descend into the boiling 

 fluid, and the other two reach no further than the vapour. These 

 tubes contain a small quantity of mercury, in which the reser- 

 voirs of the thermometers are immersed, so that these are thus 

 protected from the internal pressure. The disengaging tube of 

 the boiler communicates with a refrigerator, which serves to 

 condense the vapour ; and this refrigerator itself communicates 

 with a large reservoir of air, of which the pressure may be varied 

 at will. 



Into the boiler I put concentrated solutions of chloride of cal- 

 cium, which I caused to boil under pressures sometimes weaker, 

 sometimes stronger than the ordinary pressure of the atmo- 

 sphere, and noted the temperatures indicated simultaneously by 

 the thermometers immersed in the vapour and those which de- 

 scended into the liquid. The results obtained are given in the 

 two following tables, of which the second refers to a solution 

 containing a larger quantity of salt. 



T2 



