36 Mr. Meikle on Specific and Latent Heat, 



maintain an equilibrium, in some cases at least, between the 

 elasticities of the two gases, or between these and that of the 

 atmosphere ; but this would have had its defects. 



The experiments on the air of respiration are more liable to 

 objection; for if this was introduced into the apparatus at the 

 temperature of the lungs, it would of course be capable of 

 holding in solution more moisture than when it afterwards had 

 its temperature reduced by coming into contact with the colder 

 parts of the apparatus, especially the calorimeter, where the 

 moisture would remain condensed in a useless state* ; and the 

 air of respiration after being so deprived of its moisture would 

 be inferior in elasticity to the common air in the other parts 

 of the apparatus. If this suspicion be well founded, the result 

 ought apparently to be as is stated by Mr. H. ; for it is well 

 known, that at the same temperature, the heat in a given vo- 

 lume of elastic fluid decreases when the tension does so ; though 

 the reverse holds of the heat in a given weight. 



It may therefore be presumed that, besides what has been 

 already suggested, several sources of inaccuracy might have 

 been avoided, both in these experiments, and more particularly 

 in those of MM. Delaroche and Berard, had the process been 

 somewhat reversed, by employing gases at a temperature a 

 little above that at which they were introduced f, to cool the 

 water in the calorimeter previously raised to a still higher tem- 

 perature. 



From the above experiments, perhaps the best yet published, 

 Mr.Haycraft endeavours to draw several practical conclusions, 

 which, though very ingenious, scarcely appear to be all borne 

 out with sufficient evidence. The resistance of the air to in- 

 stantaneous expansion may, as he very properly suggests, 

 augment the temperature in the firing of gunpowder; but it is 

 doubtful if the same remark be equally applicable to the case 

 of furnaces. The resistance to expansion can never amount to 

 the force with which air rushes into an air furnace, and which 

 is always inferior to the atmospheric pressure. For air rushes 

 into a furnace in some degree as into a vacuum in a reduced 

 state of elasticity ; because it can only be from a diminution 

 of pressure on the side next the fire that the air flows towards 

 it at all. Combustion in a furnace, being a continued and re- 

 peated process, differs essentially from the instantaneous and 

 single act of explosion in gunpowder. The continued upward 



* It is true, that any vapour on condensing, gives out its latent heat ; but 

 in the present case, this would not be likely to compensate for the other 

 defect of its continuing dormant in a liquid state during the whole process. 



t For moisture in a state of aaturation often adheres to a dull or oxi- 

 dized sut face not colder than itself, 



dL->char£e 



