Specific Heat of Water and of Air

Source: Results of Experiments made with the Fumific Impeller - Specific Heat of Water and of Air
Author: Alexander Gordon, Member of the Institution of Civil Engineers
Date: Feb. 10th, 1847, London, Effingham Wilson, Royal Exchange
Appendix A

Reference to any chemical authority for the proportional quantities of heat or fuel, which uniform weights of water and of air require, in order to have their temperatures raised the same number of degrees; that is to say, a reference to the undisputed specific heats of the two bodies will prove this to be so.

The specific heat of water being 1, that of an equal weight of air is 0.2669 ; therefore, if 1 lb. of fuel is required to heat a given weight of water 1°, the smaller quantity, 0.2669 of the same fuel will suffice to heat the same weight of air 19.

Such is the result of the experiments on the specific heats of bodies by Lavoisier and Laplace, who burnt various bodies in the calorimeter, and estimated the heat by the quantity of ice melted in each experiment. These philosophers were followed by Crawford, Dalton, and Count Rumford; and the expense of heating water is determined by them to be nearly four times the expense of heating air in careful laboratory experiments.

The value of one fuel or another for the purpose of generating heat t is not a question here; but whether the body to be expanded by that heat should be water or air, is the matter before us.

Dr. Ure, in his “Dictionary of Chemistry,” art. Combustion, informs us that 1 lb. of charcoal melts on the average 68 lbs. of ice ; and by Turner's “Chemistry” (p. 57), 68 lbs. of ice melted is equivalent to 68 x 140° = 9520 lbs. of water raised 1°.

Hence it follows, that 1 lb. of this fuel raises 9520 lbs. of water 1°, or 7 8/10 lbs. of water 1212°, or 19 lbs. of water 480°; and 1 lb. of same fuel raises 35,575 lbs. of air 1°, or 29 lbs. of air 1212°, or 74 lbs. of air, 480°.

There can, therefore, be no doubt that air, by Nature, is a better body than water to work with. But hitherto Art has not accomplished the manner of doing so.

Experiments made by the calorimeter lead us to believe that:

  • 1 lb. of charcoal raises 9.520 lbs. of water 1°,
  • 1 lb. of wood raises 6.300 lbs. of water 1°,
  • 1 lb. of coke raises 13.068 lbs. of water 1°,
  • 1 lb. of coal raises 6.534 lbs. of water 1°.

But in experiments by the calorimeter there is the mechanical obstacle of the body through which the heat has to be transmitted. In the fumific impeller I have no transmission; I have chemical union. The distinction is important.

Readers disposed to pursue this part of the inquiry further, may refer with advantage to the recorded experience of Dalton and of Silvester, and to the opinions of Messrs. Donkin, Farey, Gravatt, Brunton, Simpson, Field, and Clegg, as recorded in the “Transactions” of the Institution of Civil Engineers, 4th and 11th February, 1834, paying attention to Mr. Farey's pointed observations, that any discrepancy between the theory of the specific heats and the practice of that date in warming buildings, may be “accounted for by the difficulty of bringing the air into contact with the heat produced, owing to the large space occupied by the given weight of it, as compared with that occupied by the same weight of water; 100 lbs. of water occupying a space of 1 6/10 cubic foot, whilst the same weight of air occupies 1328 cubic feet.”

The discussions which elicited the opinions of these gentlemen had especial reference to heat transmitted from the fire to the body. It was not the chemical union of bodies, which is an important feature in the Fumific Impeller.