332 Florentine Experiment. [Book VIL 



through certain cavities, and appeared in drops on 

 the furface. The condufion, however, which was 

 haftily drawn from this experiment, that water, in its 

 liquid (late, is abfolutely void of all elafticity, is not 

 warrantable. Since other experiments (hew that wa- 

 ter as well as mercury will yield, in a certain degree, 

 to the preflure of the air in a condenfmg machine, as 

 Mr. Canton proved by including it in a glafs veffeJ, 

 with a narrow neck or item nicely graduated j its con- 

 denfation appears proportioned to the force, and as 

 foon as the preffure cf the air is removed, the fluid 

 will be obferved gradually to recover its accuftomed 

 dimenfions. 



When water becomes heated to a degree beyond 

 that of the air upon its furface, the matter of heat, 

 which has a conftant propensity to diffufe itfelf equally 

 through all bodies with which it is in contact, rifes 

 and carries .in in part of the water, which it converts 

 into an elaluc fluid or vapour. Until the water, how- 

 ever, arrives at the boiling point, the evaporation is 

 very gradual j but when this happens it becomes very 

 rapid, and the part of the water which is moft heated, 

 being converted into vapour, rifes fuddenly to the fur- 

 face, and occafions confiderable agitation. 



Ebullition requires a determined degree of heat, 

 becaufe the fteam cannot be formed within the water, 

 unlefs it is ftrong enough to overcome the actual 

 preil..:e of the fluid" and air incumbent on it. But in 

 oroinu y evaporation, the vapour is formed at the fur- 

 face of I'.ie water, and has therefore no other p'-ellure 

 to overcome than that of the atmofphere. The elaftic 

 fluid, however, which is formed by ordinary evapora- 

 tion is different from that produced by ebullition, for 

 the latter always returns to the flate of water by a di- 

 minution of temperature, whereas the former is re- 

 duced 



