HEAT. 



25 



water could not be employed at the 

 temperature at which it is requisite to 

 make the experiment in this apparatus, 

 on account of the property it possesses 

 of becoming more dense in the rise of 

 its temperature from 32 to 40, oil was 

 first used. A quantity of almond oil 

 at the temperature of 32 was poured 

 into the ice cylinder, so as to cover the 

 bulb of the thermometer inch. A flat- 

 bottomed iron cup was suspended, so as 

 nearly to touch the surface of the oil, 

 and two ounces of boiling water were 

 poured into it. In a minute and a half, 

 the thermometer had risen from 32 to 

 3-2^, in three minutes to 34 i, in five 

 minutes to 36^, in seven minutes to 

 37i, when it became stationary, and 

 soon began to fall. When more oil was 

 interposed between the bottom of the 

 cup and the bulb of the thermometer, 

 the rise was less ; but even when its 

 depth was three-quarters of an inch, 

 the rise w r as perceptible, amounting 

 to U degree. With Mercury the same 

 results were obtained, the thermometer 

 rising, only with much more rapidity, 

 from the mercury being a better con- 

 ductor than the oil." 



Dr. Trail (Nicholson's Journal, Vol. 

 XII. page 127) ascertained the relative 

 conducting powers of different fluids, by 

 finding: the length of time required to 

 raise the temperature of a mercurial 

 thermometer three degrees of Fahren- 

 heit's scale, when placed in each liquid, 

 heat being applied by means of a cylin- 

 der of iron one inch in diameter, heated 

 to 212, and suspended in the liquid at 

 the distance of half an inch from the 

 bulb of the thermometer ; and that the 

 conducting power of the vessel might 

 influence the results as little as possible, 

 it was made of wood. The thermome- 

 ter placed in 



Minutes. Seconds. 



Mercury, required 15 



Saturated Solution of Sul-\ _ n 



phate of Soda J 



Water 7 5 



Proof Spirit 8 nearly. 



Solution of one part of Sul-~) 



phate of Iron, in five > 8 



parts of Water J 



Water of Potassa 8 15 



Milk of a Cow 8 25 



Saturated Solution of Sul-1 

 line. ... j 



9 



10 



phate of Alumine 



Alcohol Lond. Pharm 10 45 



Saturated Solution of Sul- 1 \ 



phate of Soda, but the 



liquid not touching I, 19 20 



the iron cylinder by I 



O.I inch, or nearly so I 



The great difficulty opposed to the 

 progress of caloric downwards, and the 

 motion of the particles by which heat is 

 conveyed through water upwards, maybe 

 further illustrated by a few experiments. 



Ex. Pour into a glass tube about 

 ten inches long and one inch in diameter, 

 a little water tinged with litmus ; then 

 fill up gradually and carefully with co- 

 lourless water : heat being applied near 

 the top, the coloured liquid will remain 

 stationary at the bottom, which it could 

 not do if it were heated and thus ex- 

 panded or made lighter ; but when 

 heat is applied at the bottom, the co- 

 loured portion will ascend and be dif- 

 fused through the whole. 



Ex. Secure a circular piece of ice to 

 the bottom of a cylindrical glass jar, 

 about twelve inches deep and four wide ; 

 cover the ice to the depth of two or 

 three inches with water at 32 : on the 

 surface of this water place, so that it 

 may float, a wooden box perforated with 

 minute holes in its sides only; then 

 pour, gently and gradually, boiling 

 water into the box, until the jar is 

 nearly full the ice will remain un- 

 melted for a very considerable time; 

 but if a similar piece of ice is placed upon 

 the surface, it will very quickly be melted. 



The slow conducting 

 power of water may be 

 illustrated by the ar- 

 rangement represented 

 at Jig. 9. A small air- 

 thermometer, capable 

 of shewing very minute 

 alterations of tempera- 

 ture, being plunged in i 

 the water of the jar, so 

 that the bulb may be a 

 little below the surface 

 ether may be inflamed 

 on the surface of the] 

 water, without affect- 

 ing the thermometer in 

 any considerable de- 1 

 gree. 



The cooling of water I 

 is very much impeded 

 by a mixture of starch, I 

 mucilage, or other sub- ' 

 stances with it, on ac- 

 count of the difficulty thus opposed 

 to the ascending motion of its particles, 

 by which the heat is prevented from 

 reaching its surface. Thus compounds, 

 such as soups, require much longer 

 time to cool than pure water. 



Ex. The circulation of the particles 

 of fluid is very pleasingly shewn by 



fiff-9. 



