Treatise on heat / By the Rev. Dionysius Lardner.

  • Lardner, Dionysius, 1793-1859.
Date:
1833
Catalogue details

Licence: Public Domain Mark

Credit: Treatise on heat / By the Rev. Dionysius Lardner. Source: Wellcome Collection.

    177/446 (page 165)
    as that of air: it is jiroportional to the pressure or elas- ticity, provided the tempernturen are. the same. If, then, we have steam raised from water under two dif- ferent pressures, and at two different temperatures, let the temperatures be equalised by applying heat to the steam of the lesser pressure out of contact with water, its pressure being meanwhile preserved. AVhen the temperatures are thus rendered equal, then their densi- ties or specific gravities will be in the same proportion as tlieir pressures.* If the space below the piston 1*, in the cylinder AB {fiy. 2.‘h), be completely filled with water, and a sufficient force be exerted on the piston to prevent it from rising in the cylinder, the water under it may be heated to any required temperature; because, no space being allowed for the formation of steam, no heat can become latent, and, therefore, all the heat com- municated to the water will be effective in raising its temperature. If the tem- perature of the water under these cir- cumstances were raised until it attained the limit of 1212°, it would have all the heat necessary to give it tlie vapor- ous form, no part of that heat being in In fact, the water would, under such circumstances, lie convertetl into vapour, in which the whole of the heat would lie sensible, and which would have no latent heat except such as the water possessed in the liquid state. If the piston, under these circum- stanci's, be raised, the water, or rather steam, 1k*1ow it, will expand, and as it expands its temperature will fall, a portion of the sensible heat becoming latent. If the piston were raised until the space below it were in- creased 1700 times, the sU'am would fall to the tem- perature of 212°, and 1000° of heat would become latent. In fact, the steam would then be identical in « See Api>eiulix, XI. II 3 Fig. 23. this case latent.