12 ON THE HEAT EVOLVED 



Being well aware that the experiments could not he accu- 

 rately performed, unless the operator should at all times pos- 

 sess a perfect control over the burning body; it became 

 necessary after attaching the box A, to insert the cross pipe 

 with the valve D, by which the current of air through the 

 stove may, in an instant, be placed at its maximum in quantity 

 and velocity, if permitted to pass through this cross pipe, in 

 place of passing through the shallow box A. 



This passage is useful when igniting anthracite coal, in which 

 process, the coal, as well as all other combustible bodies, require 

 to be heated to a certain temperature before they will ignite, 

 during which process, heat being absorbed, and not disengaged, 

 if care be taken to close this valve in proper time, none is lost. 

 As this required temperature differs not only in different bodies, 

 and in the different component parts of some bodies, but is 

 specific, for each, it may for convenience, be termed their heat 

 of ignition or accension. 



This passage is also useful in some experiments, to give a 

 momentary impulse to the inflammation, of certain bodies, and 

 cannot be dispensed with without great loss of time, in heat- 

 ing the room to its proper temperature, before commencing 

 an experiment. 



Considerable difficulty was experienced in getting the valves 

 and their appendages made with sufficient accuracy, but when 

 done, as half of the arc of each dial is divided into twenty equal 

 parts, it will be perceived that the current of air to supply the 

 body in combustion, can he regulated with great precision. 



The valve B, is particularly useful to stop at a proper time 

 the combustion of those bodies, which it is known cannot be 

 wholly consumed in the stove, and this is done almost instanta- 

 neously by closing this valve, and sliding down the hoop which 

 covers the apertures for the admission of air. 



The pipe passes through the side wall into the chimney of 

 the exterior room. Near the end of the pipe, within the in- 

 terior room, is an aperture of sufficient size to admit the bulb 

 of the thermometer E, and this aperture is closed by a tin plate 

 closely fitted to the stem of the thermometer. This plate is 



