76 HEAT OR CALORIC 



consequence of the diversity of the colors, a well defined line of 

 separation is soon visible.*' 



" The phenomena of this interesting experiment may be thus ex- 

 plained." 



" If the upper portion of a vessel, containing a fluid, be heated ex- 

 clusively, the neighboring particles of the fluid, being rendered light- 

 er, by expansion, are more indisposed, than before, to descend from 

 their position. But, if the particles, forming the inferior strata of the 

 fluid in the same vessel, be rendered warmer than those above them, 

 their consequent expansion and diminution of specific gravity, causes 

 them to give place to particles above them, which, not being as 

 warm, are heavier. Hence, heat must be applied principally to the 

 lower part of a vessel, in order to occasion a uniform rise of tempe- 

 rature in a contained fluid." 



" This statement is equally true, whether the fluid be aeriform, or a 

 liquid, excepting that in the case of aeriform fluids, the influence of 

 pressure on their elasticity, may sometimes co-operate with, and at 

 others oppose, the influence of temperature." 



7. Process by which caloric is distributed in a liquid before it boils. 



"On the first application of 

 heat to the bottom of a vessel con- 

 taining cold water, the particles 

 in contact with the bottom are 

 heated and expanded, and con- 

 sequently become lighter in pro- 

 portion to their bulk, than those 

 above them. They rise therefore, 

 giving an opportunity to other 

 particles to be heated, and to rise 

 in their turn. The particles 

 which were first heated, are soon, 

 comparatively, colder than those 

 by which they were displaced, 

 and, descending to their primi- 

 tive situation, are again made to 

 rise, by additional heat, and en- 

 largement of their bulk. Thus 

 the temperatures reversing the 

 situations, and the situations the 



* "I used to perform this experiment with an inclined tube, as suggested in 

 Henry's Chemistry. The modification here given, is so far a contrivance of my 

 own, as relates to the use of the heater, tin cap, and iron ring ; and the employment 

 of two colors instead of one. On account of the liability of the glass to crack, I 

 found the old method very precarious, when a tube was used large enough to show 

 the phenomena advantageously." 



