22 M. V. Regnault on the Elastic Forces of Vapours 



The preceding experiments relate to the elastic force of the 

 vapours furnished by mixtures of volatile liquids in the static 

 condition, that is to say, when the space containing the liquid 

 and the vapour is kept at a constant temperature. It became 

 interesting to study them in the dynamic state, that is to say, to 

 determine the temperatures presented by the vapour and the 

 liquid when the mixture is boded under different pressures. 

 My experiments have hitherto been made only upon liquid mix- 

 tures of the first class, i. e. upon those composed of liquids which 

 exert no sensible solvent action upon each other, and which con- 

 sequently remain superposed. 



Here we must distinguish two cases ; that in which the more 

 volatile liquid forms the upper stratum, and that in which it 

 forms the lower. It is to the latter that I have principally 

 directed my attention, as it is for this that we may hope to obtain 

 the most constant results ; the vapour of the more volatile liquid 

 is then compelled to traverse the less volatile supernatant liquid, 

 and is therefore placed in favourable conditions for becoming 

 saturated with it. Nevertheless the phsenomenon appears to be 

 very complex, because it depends upon the greater or less vivacity 

 of the ebullition. When the ebullition is weak, its temperature 

 is found to be that at which the sum of the tensions of the two 

 vapours is in equilibrium with the pressure opposed to the ebul- 

 lition ; but if the fire be rendered more active, the ebullition 

 becomes very violent, the temperature rises, and finally attains 

 the point at which the more volatile liquid would boil under the 

 same pressure if it were alone. It is probable that passages are 

 then formed in the upper stratum of liquid, and that the vapour 

 passing without obstacle does not sensibly carry up vapour from 

 the less volatile liquid. These irregularities are particularly 

 remarkable when ebullition takes place under low pressures. 



Part V. — Researches undertaken to determine whether the solid 

 or liquid state of bodies exerts any influence upon the elastic 

 force of the vapours ivhich they emit at the same temperature 

 in vacuo. 



In my preceding researches upon the elastic force of aqueous 

 vapour, I have endeavoured to ascertain whether the solidifica- 

 tion which water undergoes when its temperature descends below 

 0° C. exerts any influence upon the tension of its vapour. For 

 this purpose I made a great number of determinations of the 

 elastic force of the vapour emitted by ice between —32° and 0° C. 

 I have ascertained that the curve constructed upon these experi- 

 ments presented a perfect continuity with that given by the 

 elastic forces of the vapours furnished by liquid water at tempe- 

 ratures above 0° C. 



