SOURCES OF HEAT AND COLD. 



13] 



(c.) Chemical action without combustion; that is to say, without 

 combustion to begin with ; combustion is not used as a means of rais- 

 ing the heat, although this mode of evolving heat may end in com~ 

 bustion, provided any ingredient in the mixture is combustible ; e. g. 

 as in the case of nitric acid acting on alcohol or oils, dense or vola- 

 tile. Fermentation of hay may produce combustion. 



Spontaneous combustions proceed in many instances, from chem- 

 ical action, as in cases where oils, tallow, paints, and similar sub- 

 stances, are in contact with flax, cotton or hemp. Tanner's bark 

 and horse manure, by fermentation, produce heat for the green 

 house, and for some processes in the arts. 



Most of the cases under this head belong to capacity and specific 

 heat, and the doctrine has been partly anticipated. Many more in- 

 stances will follow. At present I add only the following from Dr. 

 Hare. 



5. Boiling heat produced, by the mixture of sulphuric acid vnth 

 water. 



" Into the inner tube, represented in the 

 adjoining figure, introduce about as much 

 alcohol, colored, to render it more discern- 

 ible, as will occupy it to the height of three 

 or four inches. Next pour water into the 

 outer tube, till it reaches about one third as 

 high as the liquid within ; and afterwards 

 add to the water, about three times its 

 bulk of concentrated sulphuric acid. The 

 liquid in the inner tube will soon boil vio- 

 lently, so as to rise in a foam." 



6. Chemical combination, attended by decomposition, as the means 

 of evolving caloric. 



" Instances of that species of corpuscular reaction, which comes un- 

 der this head, will be hereafter mentioned in their proper places. The 

 extrication of caloric, which is usually more or less a consequence of 



