10 



HEAT. 



Graham, and consisted in substituting 

 for the usual bob of the pendulum, a 

 glass cylinder, about six inches deep, 

 holding about ten or twelve pounds of 

 mercury. When the suspending steel 

 rod expanded by heat so as to lengthen 

 the pendulum, the mercury, by its ex- 

 pansion, raised the centre of oscillation 

 as much as the increased length of the 

 steel rod occasioned it to be depressed. 

 But the plan most usually adopted for 

 clocks, is the invention of Harrison, and 

 is called the gridiron pendulum ; it 

 consists of a combination of bars, three 

 of which are of steel, and two com- 

 pounded of zinc and silver. These 

 are so arranged, and the weight is sus- 

 pended in such a way, that the expan- 

 sion occasioned by heat in the steel is 

 counteracted by the expansion of the 



other metal, so as to keep the pendulum 

 always of the same length. 



The contrivance applied by Arnold to 

 watches, for the purpose of preventing 

 the injurious effects of expansion and 

 contraction, is upon the same principle, 

 and is called the compensation balance : 

 in the construction of which, interrupted 

 concentric rings of different metals are 

 joined together, so that the expansion 

 of one counteracts the expansion of the 

 other. 



The expansibility of fluids by heat is 

 still greater than that of solids, and the 

 differences which they exhibit among 

 themselves are more striking. Mer- 

 cury does not expand so much as water, 

 water not so much as spirit of wine, and 

 spirit of wine is not so expansible as 

 ether. 



The following TABLE of the expansions produced in liquids by being heated from 32 to 

 212 is from Dr. Ure's Dictionary of Chemistry. 



Mercury . . . , Dalton * 



Do Lord Charles Cavendish 



Do Deluc ." 



Do General Roy 



Do Shuckburgh 



Do Lavoisier and Laplace . . 



Do. , Haellstroem 



0.020000 

 0.018870 

 0.018000 

 0.017000 

 0.01851 

 0.01810 

 0.0181800 

 Do Dulong and Petit 0.0180180 



Do. .. 

 Do. .. 

 Do. .. 

 Do. .. 

 Do. .. 



Water 



0.0158280 

 0.04332 28-W 

 0.0600 iV 



Do. from 212 to 392 0.0184331 



Do. from 392 to 572 .... 0.0188700 



Do. in Glass from 32 to 2 12 0.015432 



Do. Do. from 212 to 392 0.015680 

 . Do. Do. from 392 to 572 

 f Kirwain, from 39 its maxi- \ 

 \ mum density J 



Muriatic Acid (sp. gr. 1.137.) Dalton* 



Nitric Acid (sp. gr. 1.40) Do 0.1100 



Sulphuric Acid (sp. gr. 1 .85) Do . 0600 



Alcohol Do 0.1100 



Water. Do 0.0460 



Water saturated with common salt Do . 0500 



Sulphuric ^Ether Do . 0700 



Fixed Oils Do 0.0800 



Oil of Turpentine Do 0.0700 



Water, saturated with common salt . . Robison 0.05198 



ss-52 

 V* 



SS-W 

 5 4- *2 5 



es-Va 



Ex. The expansion of a liquid may 

 be strikingly shown, by filling a glass 

 bulb, having a long tube attached to it, 

 with the liquid, so that it may rise a 

 small part of the way upwards in the 

 tube ; the bulb being set upon a stand, 

 and heat applied under it, the bulk of 

 the liquid will be enlarged, as will be 

 seen by its rising higher in the tube. 

 This effect is produced notwithstanding 

 the expansion of the glass which occa- 

 sions its capacity to be enlarged. 



Ex. Or the expansion of water may be 



shown by partly filling a bulb and tube, 

 like that described in the last experi- 

 ment, with coloured water : immersion 

 in a jar of hot water will occasion 

 the water contained in the bulb and 

 tube to expand and ascend higher. 

 (Fig. 3.} 



Those liquids are the most expansi- 

 ble which require the least heat to make 

 them boil. 



Ex. Equal quanties of heat applied to 

 liquids do not occasion equal degrees 

 of expansion : this may be shown by ap- 



*. The tiuantities given by Mr. Dalton are, probably, too great, as is certainly the case with Mercury; his 

 experiments being, perhaps, modified by his hypothetical notions. 



