316 On the Rapid Production of Steam. 



water by mixture, involves the necessity of considering the increase 

 of temperature, in the containing vessel, together with its separate 

 specific heat, before any accurate result can be anticipated. The 

 method of generating steam from an apparatus kept at a uniform 

 temperature, and by means of bodies of known superior temperatures, 

 is, I conceive, less liable to objection from any of these sources of 

 fallacy. The only modifying cause, which deserves much attention, 

 is the barometric pressure during the experiment, which involves also 

 a consideration of the specific heat of steam under different press- 

 ures, but as this source of error may be obviated by performing ex- 

 periments at uniform pressures, we need hardly take it into view, in 

 estimating the general correctness of the mode now proposed of 

 verifying the specific heats of bodies. 



By knowing at what temperature we plunge a piece of metal un- 

 der boiling water, the weight of the metal, and its mean capacity for 

 heat, we may readily infer, from what is known of the quantity of la- 

 tent heat in the unit by weight of steam, what weight of the liquid 

 will be boiled off while the metal is reduced from a superior tem- 

 perature down to 212°. 



Thus let the lemperature of the metal above 212° =t 



Its iveight =^w 



Its mean cavcicity between 212° and the known temperature =c 



The \dXer\iMat of atmospheric steam =1 



The weight of steam which the metal can produce =s 



tew 

 Then will «=-/-" Thus, suppose ^=2000°, c=.llll, w=lGoz. 



tcio 2000X. 1111X16 

 and Z=990°, then we shall have —r~ oqa = 3,571 



ounces. 



From the above formula we derive immediately an expression for 



the temperature vfhen all the other elements are known ; for Is = tew, 



Is J 

 whence ^= — ?'so that when we would determine the actual tem- 



civ 



perature of a body above 212°^ whose specific caloric has been care- 

 fully ascertained, we have only to Ji.nd what weight of vapor it will 

 produce in coming doivn to the point of ebullition ; multiply this by 

 the latent heat in steam, and divide the product by the product of the 

 iveight of heated matter midtipli^d by its specific heat. Upon the 

 basis of this proposition I have constructed an instrument called the 

 steam: pyrometer, to be applied to the measurement of heat in incan- 



