The elements of medical chemistry : embracing only those branches of chemical science which are calculated to illustrate or explain the different objects of medicine, and to furnish a chemical grammar to the author's Pharmacologia . y therefore be said to carry, ratherthan to conduct heat. The portion of the fluid which isthe nearest to the source of heat expands, and, consequentlybecoming specifically lighter, ascends, and is replaced by acolder portion from above. This, in its turn, becomes heatedand dilated, and gives way to the second colder portion ;and thus the process proceeds, as lon^
The elements of medical chemistry : embracing only those branches of chemical science which are calculated to illustrate or explain the different objects of medicine, and to furnish a chemical grammar to the author's Pharmacologia . y therefore be said to carry, ratherthan to conduct heat. The portion of the fluid which isthe nearest to the source of heat expands, and, consequentlybecoming specifically lighter, ascends, and is replaced by acolder portion from above. This, in its turn, becomes heatedand dilated, and gives way to the second colder portion ;and thus the process proceeds, as lon^ as the fluid is capableof imbibing heat. This is illustrated by a very simple ex-periment. Exp. 41.—Let a sensible thermometer (an air thermome-ter) be inverted in a vessel of water, so that the ex-tremity of the bulb is barely beneath the surface ; thenpour a little aether upon the water so as to forma stratum about one eighth of an inch abovethe thermometer, and let the aether be in-flamed, as represented in the annexed delicate may be the thermometer,the air in it will not soon expand ; theaether boils violently, but a very long processof this kind is required to communicate anysensible heat to the 289. From such facts Count Rum ford concluded, thatwater is a perfect non-conductor of caloric, propagating it inone direction only, viz. upwards, and that in consequence ofthe motions which it occasions among the particles of thefluid. This inference, however, has been set aside by theinquiries of Dr. Thomson and Dr. Murray, from which itappears that water is a conductor, though a very slow andimperfect one. 290. Besides these modes, by which changes of temperatureamong bodies are propagated, either by caloric being com-municated from particle to particle, or by its being transport-ed by change of place in the matter which receives it, orfrom which it is abstracted, there is still another mode,—thatby Radiation, or projection from the surface of bodies,
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