rt<f MtfceUaneous Experiments on Heat. 



difference between one bod» and another but what arifes from this circumllance ; — that 

 thcfe points being changeable by combination, give rife to a prodigious number of confc- 

 quences different from thofe which obtain in the fimpler eleinents. We muft refer to the 

 o'riginal Effay for the more ample elucidation of thefe points, where chemical philofophers 

 will fee the outline traced of an immenfe field of rcfearch, which, if it fhould not inf.lLiJe the 

 whole of the phenomena which have been dellgnated under the name of eledtive attraclion, 

 ^ill certainly comprehend a large mafs of effc£ts which never fail to prefent themfelves in 

 every natural change which comes under our notice. 



Chap. IV. The laft and concluding chapter contains a variety of mifcellaneous experi- 

 ments. I. If a thermometer with a long cylindrical bulb being at the temperature of the air 

 in fummer, or any temperature above the freezing point, be pl^unged to half the length of its 

 bulb in ice and water, the mercury will fal; in the tube only half as much as if the whole 

 bulb had been immerfcd. This experiment fucceeds equally well, when the fuperior half of 

 the bulb is covered with a flieath lined with foft fur to prevent the communication of heat 

 from the air during the experiment. It (hews that the upper half of the mercury is not 

 coole"d, or, in other words, that heat does not pafs downwards in fluids. — 2. Ice-cold water 

 {landing on ice at the bottom of a thin tube of glafs, may be boiled by hoidmg the tube in- 

 clined over the flame of a candle applied near the upper end, and gradually removed lower 

 <lown as the ebullition proceeds. In this way all the water in the tube may be brought into 

 the moft violent ebullition, to within a quarter of an inch of the ice, before this begins to 

 ■ te melted. — 3. The radiant heat from a red hot iron bullet w;is not found to make its way 

 downwards through liquid water, nor through mehed tallow, nor melted wax. The experi- 

 rrient was tried on a thermometer about a quarter of an inch beneath the furface of each of 

 thefe fluids. Thefe fa6ls are analogous to the obfervation of Scheeie, who found that 

 radiant heat does not pafs through glafs. When the red-hot ball was held over a cake of 

 ice, the heat appeared to be tranfmitted by communication, though very flowly. The 

 excavation- ui. ice was deepeft near the middle. The contrary was the cafe both in tallow 

 and in wax. Count Rumford does not direftly explain the caufe of this remarkable differ- 

 ence. It is the only immediate faft I recolleft having feen in his Effays, in proof of the affer- 

 tibn that water (lands alone, with regard to the property of expanding in the lower degrees 

 •of refrigeration; and confequently of contracting as its temperature increafes in that part 

 of the fcale. From this property it would follow, that a warm ftream of water muft de- 

 fccnd immediately beneath the bullet, while an afcending current obtains near the circumfer- 

 ence of the cavity. But if the expanfion of tallow be uniform from the earlieft point of 

 fufion, the heated fluid will not defcend, but will fpread out Tideways, and circulate in a con- 

 trary diretSlion to the current in water ; while the afcending ftream of cold fluid will be 

 near the centre, and will defend part of the tallow in that region from being fufed.— 

 4i, Beautiful cryftals of fea fait were formed in brine ftand^ng on mercury in an open veflel 

 for half a year. The Count makes it a queftion, whether the mercury contributed in any 

 manner to this effe/i? It feems probable that it did not, and that evaporation equally flow 



and undifturbed would have affvirded the fame refult in other circumftances e. A fimilar 



remark may be made on his obfervation of olive oil rendered colourlefs by expofure to the air 

 for fix months upon brine, in a place where the fun's rays never enfc ed. ] he fame effc(5l bap. 

 pens to dlive oil which remains in unclofed veflels in work-(hops.-- 6. Part of the laft-men- 



D tioneil 



