CHEMISTRY. 



35 



Element* nutcr to cool a given number of degrees in the differ- 

 / ent gases, will give the reader some idea of their re- 

 rhenmtry. j at ] ve conducting powers. 



Seconds. 



Rate of Carbonic acid, 112 



cooling i:i Sulphurettd hydrogen, T 



B 6 *- Nitrous oxide, S- 100 + 



Olefiant gas, J 



Common air, T 



Oxygen, MOO 



Azotic ga, J 



Nitrous gas, 90 



Gas from pitcoal, .... 70 

 Hydrogen gas, 40 



S EOT . III. Of the equal Distribution of Tempei-ature. 



Oftheequal When substances of different temperatures are 

 diitnhu- placed in each other's neighbourhood, the hotter 

 n " bodies become colder, and the colder acquire heat, 

 and the changes continue till all the bodies acquire 

 the same temperature. This property of caloric of 

 distributing itself equally, has been called the equili- 

 brium of caloric. It might with more propriety be 

 called the egual distribution of temperature. 



It had been taken for granted by Sir Isaac New- 

 ton, and was proved by the experiments of Krafft 

 and Richmann, that when a body is suspended in a 

 medium of a temperature different from its own, the 

 difference between the temperature of the body and 

 the medium diminishes in a geometrical ratio, while 

 the time increases in an arithmetical ratio ; or, which 

 comes to the same thing, that in given small times, 

 the heat lost is always proportional to the heat re- 

 maining in the body. 



SECT. IV. Of the Effects of Caloric. 



Of the The changes which caloric produces on bodies 



effects of may be arranged under three different heads ; namely, 

 caloric. j Changes in bulk; 2. Changes in ate ; and 3. 

 Changes in combination. 



1. C/tanget in Bulk. 



Change* in Every addition or abstraction of heat produces a 



bulk. corresponding change in the bulk of the body affect- 



ed. In general, the addition of heat produces ex- 

 pansion, and the abstraction of it produces a diminu- 

 tion of bulk. To this general law there are perhaps 

 one or two exceptions. 



Cipansion The expansion of gases by heat is greatest, that of 

 liquids much smaller, and that of solids smallest of all. 

 Thut, 100 cubic inches of air by being heated from 

 32 to 212 D , expand to 137.5 inches. The same 

 augmentation of temperature makes 100 cubic inches 

 of iron, by the same increase of temperature, expand 

 only to 100.1 inches. 



of gate*. All gases undergo the same expansion by the same 



augmentation of temperature, and the same contrac- 

 tion by the same diminution of temperature. This 

 change is nearly equable, though it is a little less at 

 bigh temperatures than at low. From the most 

 exact experiments hitherto made, we may conclude, 

 3 



that air and all gases expand about 3 ^r part of their Elcmw, 



bulk for every degree of heat thrown into them. '.' ,. 



, ' . c T Cheniisfr* 



From the experiments of Gay-Lussac, it appears ^__ __ 



that the steam of water and the vapour of ether un- 

 dergo the same dilation as air, when the same addition 

 is made to their temperature. Hence it is reasonable 

 to conclude, that all elastic fluids expand equally and 

 uniformly by heat. 



The expansion of liquids differs from that of elastic Liquids, 

 fluids, not only in quantity, but in the want of uni- 

 formity. Every liquid has a peculiar expansion of 

 its own, different from that of every other liquid. 

 The expansibility is greater when the temperature is 

 high, than when it is low. Alcohol expands most of 

 all the liquids hitherto tried ; 100,000 parts of it at 

 32, become 104.162 at 100. Nitric acid is the 

 next in order, then lintseed oil, then oil of turpentine, 

 then sulphuric acid, then water, and mercury is the 

 least expansible of all the liquids hitherto tried. 



The solids expand much less than the liquids. As Solid> 

 far as observation has gone, their expansion is equable, 

 or at least their deviation from it is insensible. 

 100,000 parts of glass at 32, become at 100,083 at 

 21 2". The order of the expansibility of the principal 

 metals is as follows, beginning with the least expan- 

 sible. Platinum, gold, antimony, cast-iron, steel, 

 iron, bismuth, copper, brass, silver, brass-wire, tin, 

 lead, zinc. 



The property which bodies have of expanding Thermo- 

 when heat is applied to them, has suggested an in- meter. 

 strument for measuring the relative temperatures of 

 bodies. This instrument is the thermometer. A. 

 thermometer is a hollow tube of glass hermetically 

 sealed, and blown at one end into a hollow globe or 

 bulb. The bulb and part of the tube are filled with 

 mercury. When the bulb is plunged into a hot bo- 

 dy, the mercury expands, and of course rises in the 

 tube ; when it is plunged into a cold body, the mer- 

 cury contracts, and of consequence sinks in the tube. 

 Thermometers are made in this way. The requisite 

 quantity of mercury being introduced, the thermo- 

 meter is plunged into melting snow, and the place 

 where the mercury stands is marked. This is called 

 the freezing point. The thermometer is then plun- 

 ged into boiling water, and the point at which the 

 mercury stands marked. This is called the boiling 

 water point. The distance between these two points 

 is divided into a number of equal parts called de- 

 grees, and these degrees are continued indefinitely 

 above and below these two points. 



The thermometer gets its name according to the 

 number of degrees into which the space between the 

 freezing and the boiling point is divided. There are 

 four thermometers still used in Europe. In that of 

 Reaumur, the space between the two points is divi- 

 ded into 80. The freezing point is marked 0, the 

 boiling point 80. In the thermometer of Celsius, 

 the same space is divided into 100. The freezing 

 point is marked 0, the boiling point 100". This it 

 the thermometer used in Sweden and in France since 

 the revolution. In the thermometer of Fahrenheit, 

 the space between the two points is divided into 1 80. 

 But the scale begins at the cold produced by a mix-** > 

 ture of snow and salt, which is 82 below the free- 

 zing point. The freezing point is marked in conse- 



