374 On M ie Heat developed in Combustion 



The reservoir of this thermometer is cylindrical, 

 about two lines in diameter only, and four inches high ; 

 and as the water in my calorimeter is four inches deep, 

 this thermometer always indicates the mean temperature 

 of the fluid, whatever may be the temperature of its 

 different strata. 



In my various inquiries concerning heat, I have had 

 frequent opportunities of seeing the importance of this 

 precaution ; and I cannot conceive how any one can 

 expect to avoid great mistakes in measuring the temper- 

 ature of liquids heated or cooled, if we do not attend 

 to this. For my own part, I confess I pay little regard 

 to the experiments of which I am told, when I know 

 they are so negligently made ; and assuredly I shall 

 never waste my time in attempting to build theories on 

 their results. 



In using the apparatus I have described, several pre- 

 cautions are necessary. In the first place, it is obvious 

 that when the object is to ascertain the quantity of heat 

 developed in the combustion of any inflammable sub- 

 stance, it is indispensably necessary so to arrange mat- 

 ters that the combustion shall be complete. I have thought 

 that it might be so considered, whenever the substance 

 burned leaves no residuum, and burns with a clear 

 flame, without smoke or smell. 



The least smell, particularly that peculiar to the in- 

 flammable substance burned, is a certain indication that 

 the combustion is imperfect. 



I had long sought, before I was able to find, to my 

 satisfaction, a mode of burning very volatile liquids, 

 such as alcohol and ether ; but I have at length discov- 

 ered it, as will soon appear. I have frequently suc- 

 ceeded in burning highly rectified sulphuric ether, with- 



