New conversations on chemistry : adapted to the present state of that science, wherein its elements are clearly and familiarly explained : with one hundred and eighteen engravings illustrative of the subject, appropriate questions, a list of experiments, and a glossary : on the foundations of Mrs. Marcet's "Conversations on chemistry" / by Thomas P. Jones.

  • Jones, Thomas P., 1774-1848.
Date:
1833
Catalogue details

Licence: Public Domain Mark

Credit: New conversations on chemistry : adapted to the present state of that science, wherein its elements are clearly and familiarly explained : with one hundred and eighteen engravings illustrative of the subject, appropriate questions, a list of experiments, and a glossary : on the foundations of Mrs. Marcet's "Conversations on chemistry" / by Thomas P. Jones. Source: Wellcome Collection.

Provider: This material has been provided by the National Library of Medicine (U.S.), through the Medical Heritage Library. The original may be consulted at the National Library of Medicine (U.S.)

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    have dipped each of them into melted wax, and by this I have cemented a piece of card to the end of each. We shall find on healing tlicm that the silver is the best conductor, next the copper, and then the iron, whilst the lead is very inferior to either of the others. Observe the wax is melting first upon the silver;—and now the piece of card has fallen from it. Emily. The pieces have fallen from each in the order in which you named them, and the difference between them has proved to be much greater than I expccted(.3). Mrs B. You have seen that although all solids are conductors of heat, they vary greatly from each other in this respect. In speaking of air it was mentioned us a very bad conductor, and you are to understand the same of all fluids, v i.ether elastic or non-elastic(4). That distinguished philosopher, Count Rumford, who investigated this subject with much care, considered fluids as being absolutely non-conductors, and believed that if their parlicles could be kept from motion among themselves, it would be impossible to heat them throughout(5). Caroline. How could the Count think so, as we know that they are ca- pable of imparting heat to, or taking it from us, accordingly as they are hotter or colder than we are? Emily. And how, if the particles of water do not communicate heat to each other, does that which is contained in a vessel over the fire become hot throughout(6)? Mrs B. Count Rumford admitted that solid bodies would communicate heat to the particles of fluids which were in contact with them, and that fluids would in like manner communicate it to solids, but denied that any such interchange took place between the particles of fluids them- selves^). With respect to Emily's question, the particles of fluids,you know, move with the most perfect facility among themselves, and you are also aware that fluids are expanded by heat, and consequently rendered specifi- cally lighter; it was to these two circumstances that the Count attributed the diffusion of heat in fluids. When a vessel containing water is placed upon the fire, the bottom of it becomes healed, and communicates its heat to the particles of water in contact with it; these becoming ex- panded, and consequently lighter than the portions above, rise to the sur- face and leave a new layer of particles to be acted upon in the same way. This change of place continues until the whole of the water has arrived at the boiling point; the heat not being communicated from particle to parti- cle, but conveyed, or carried by the currents which are established(8). Caroline. This accounts most ingeniously for the propagation of heat upwards; but supposing you were to heat the upper surface of a liquid, the particles being specifically lighter than those below, could not descend. How, therefore, would the heat be communicated downwards? Mrs B. Had the Count's assumption been absolutely correct, a liquid could not be heated from above(9); and indeed, although this does take place, it is effected so slowly, that he believed the heat was, in every case, conducted down by the solid vessel in which the fluid must be contained; the effect being more or less slow as this is a good or bad conductor(lO). 3. How may the difference in the conducting power of metals be shown? 4. Are fluids good conductors? 5. What opinion did Count Rumford entertain upon this point? 6. What objections are urged to this opinion of Rumford? 7. How did Rumford suppose heat to operate between solids and fluids? 8. In what way did he suppose that heat was diffused in a fluid? 9. Whv would not this account for heat descending in a fluid? 10. How did Rumford suppose the descent to be effected?