420 Mr, Ilerapath on the Injiuence of Humidity [June, 



600°. This table generalized may be represented by the for- 

 mula : 



Latent heat + F - 32 = 1196, or latent heat = 1228 - F, 



in which F is the Fahrenheit temperature of the steam. There-^ 

 fore as the temperature of the steam increases, the latent heat of 

 it diminishes, and at 1228° is nothing. Hence at 1228° water 

 may change its state ; that is, from the fluid to aeriform, or vice 

 versa, and neither " combine with nor separate from caloric," 

 Now in Dr. Thomson's Chemistry, vol. i. p. 73, he tells us that 

 the law of Dr. Black, who was the contriver of this latent heat, 

 *' in its most general form, may be stated as follows : Whenev>era 

 body changes its state, it either combines with caloric, or separates 

 from caloric." Hence Dr. Black's law " in its inost general 

 form " is in direct opposition to a '* general law " which Dr. 

 Thomson has deduced from the experiments of Messrs. Cle- 

 ment and Sharpe. What other conclusion can be drawn from 

 these jarring and contradictory laws but this, I really cannot 

 perceive ; namely, that either Dr. Black's law of latent heat 

 ** in its most general form " is wrong, or the experiments con- 

 taining " the property of vapours," to which Dr. Thomson is 

 anxious to draw the attention of chemical philosophers, are 

 themselves incorrect. 



I shall make no observation on the results given by the expe- 

 riments of Ure and Rumford, which I have discussed in another 

 place, and shown to be very contrary to those it seems flowing 

 from Sharpe and Clement's ; but there is a consequence of the 

 latter experiments so truly strange, that I find a difficulty in con- 

 ceiving how it can be even possible. When water is heated 

 above 1228°, the latent heat by these experiments becomes 

 negative ; that is, instead of heat being lost by the conversion 

 of water into steam, there is an acquisition of heat ; and con- 

 versely, by the conversion of steam into water, there is a loss of 

 heat. Consequently if when the temperature is above 1228° 

 steam is to be generated, and the same temperature maintained, 

 we must not, as in other cases, increase the neat, but diminish it, 

 and lighten the pressure a little. And in order to condense the 

 steam and preserve the same temperature, we must somewhat 

 compress the steam, and increase the temperature ! Can this be 

 right ? Can nature work by laws so utterly repugnant to all ana- 

 logy and parallel, and so positively contradictory to themselves? 

 I know not whether I can myself see correctly, but I cannot 

 perceive any difference in the relation of steam to water at 1500°, 

 and in the same relation at 1000°. The one appears to me to be 

 as much an air, and the other as much a fluid at the former tem- 

 perature as at the latter ; and thence I should conclude the con- 

 version of water into steam at either temperature is still the same 

 operation on the same fluid ; and must consequently require the 

 ■ame means or cause. 



