132 THERMOMETER. 



which is evolved escapes from the water in consequence of 

 its changing from a liquid to a solid form by its union with 

 the lime. When solid bodies become liquid or gaseous, 

 their capacity for caloric is proportionately increased. If 

 you place a glass of water in a mixture of equal quantities 

 of snow and salt, during their conversion to a liquid, the 

 water will be frozen in consequence of parting with its ca- 

 loric to supply the increased capacity of the mixture. 



The portion of caloric necessary to raise a body to any 

 given temperature is called its specific caloric. The instru- 

 ment in common use for measuring the temperature of bodies 

 is called a Thermometer. It consists of a glass tube con- 

 taining a portion of mercury, with a graduated scale annex- 

 ed to it. It is constructed in the following manner. A 

 small bulb is blown on the end of the tube, and this bulb 

 and a part of the tube are to be filled with mercury which 

 is to be heated till it boils. This ebullition forces out the air 

 and the tube is hermetically sealed while the mercury is 

 boiling. The next object is to construct the scale. It is 

 found by experiment, that melting snow or freezing water is 

 always at the same temperature. If, therefore, a thermo- 

 meter be immersed in the one or the other, the mercury will 

 always stand at the same point. It has been observed, too, 

 that water boils under the same pressure of the atmosphere 

 at the same temperature. A thermometer, therefore, im- 

 mersed in boiling water, will uniformly stand at the same 

 point. Here, then, are two fixed points, from which a scale 

 may be constructed, by dividing the intermediate space into 

 equal parts, and carrying the same divisions as far above and 

 below the two fixed points as may be wanted. When a ther- 

 mometer is brought in contact with any substance, the mer- 

 cury expands or contracts till it acquires the same tempera- 

 ture ; and the height at which the mercury stands in the 

 tube, indicates the exact temperature of the substance to 

 which it has been applied. It will. not show the absolute 

 caloric in substances ; for it cannot measure that portion 

 which is latent, or chemically combined with any body. 



Caloric is the cause of fluidity in all substances capable of 

 becoming fluid, from the heaviest metal to the lightest gas. 

 It insinuates itself among their particles and invariably se- 

 parates them in some measure from each other. Thus ice 

 is converted into water, and by a further portion of caloriC; 



