TRANSACTIONS OF THE SECTIONS. 165 



On the Quantity of Heat developed by Water when violently agitated. 

 By George Rennie, F.R.S. S(C. 



Our knowledge of the mechanical properties of heat was very limited until the 

 jear 1798, when Count Rumford published his valuable paper " On the Source of 

 Heat excited by Friction." The investigations of Dr. Black, and subsequently of 

 Watt, Southern, Creighton and Murdoch of Soho, and of Lavoisier, Mongolfier, 

 Dulong, Seguin, Mayer, &c. on the Continent, have been engaged in similar re- 

 searches ; while the chemical or mechanical properties of heat have been largely 

 augmented by Dalton, Leslie, Taylor, Davy, Faraday, Hesse, and Thomson. The 

 question may be considered — 



1st. As to the effects of electric action in separating or decomposing compound 

 bodies. * 



2ud. The effects of the compression and extension of solids and fluids. 



3rd. The effects of the chemical affinity of acids on metallic or saline bases, in 

 which may be included the spontaneous combustion of metals, fossils, and fibrous 

 substances. 



4th. The condensation and expansion of fluids and gases. 



All these have attracted the attention of modern philosophers, among whom may be 

 cited the names of Andrews, Graham, Joule, Thomson, Rankine, and of M. Regnault, 

 whose magnificent experiments, under the auspices of the French government, and 

 published in the year 1847, and since continued in a second part, have developed, 

 more fully than hitherto, new values of the calorific and specific heat of water under 

 different states of density, and temperature, and of other elastic fluids. He found 

 the calorific capacity of water to be double that of ice or steam, a quality which 

 would tend to prove that liquid water has a different molecular arrangement from 

 that of ice or steam. 



But it is owing to the more recent experiments of Mr. Joule, communicated to the 

 Philosophical Society of Manchester in 1843, to the British Association in 1847 and 

 1848, and afterwards to the Royal Society in 1849, that we became first acquainted with 

 the numerical value of heat as a mechanical power. Mr. Joule's experiments* were 

 made on three different fluids, water, oil, and mercury ; and in all the three cases 

 the remarkable result appeared, viz. that the mechanical power represented by the 

 force necessary to raise 774-88 lbs. one foot high, produced a quantity of heat equal 

 to the temperature of 1 lb. of water raised 1° Fahrenheit. This equivalent was after- 

 wards altered by an improvement in the apparatus with which he experimented to 

 71 libs. ; thus confirming the experiments of Rumford and Davy on the friction of 

 solids, and proving that the heat of elastic fluids consists simply in the vis viva of 

 their particles. In the years 1845 and 1847, Mr. Joule employed an agitator to 

 agitate water, oil, and mercury in a box, to produce fluid friction on the principle of 

 common paddle-wheel, by which means he obtained equivalents of 781'5, 782'1, and 

 787'6 respectively. 



These and other experiments left no doubt in his mind as to the existence of an 

 equivalent relation between force and heat. The care bestowed upon these experi- 

 ments in deducting the retarding influences entitle them to every credit. Upon 

 examining the Table showing the results, it does not appear that the temperature of 

 the water had been raised more than 0-563209°, say half a degree to 97470-2 grains, 

 or as 1 to 7-84229 lbs. of water, and to a higher temperature, and for mercury, than 

 31-31. It is desirable, therefore, that these experiments be extended. 



Having long entertained the idea that steam, as applied to the movement of en- 

 gines, lost a large portion of its heat in the act of transmission, I watched carefully 

 the attempts which had been hitherto made by inventors for improvements in the 

 appUcation of it through the medium of atmospherical air, such as by Neipce in 

 France in 1806, by Sir George Cayley in 1807 and 1838, by Sterling in 1816, by 

 Erichson in 1826 and 1830, by Brown with his hydrogen gas-engine in 1823, and 

 by Du Trembley's combined steam and ether engine in 1846; and its subsequent 

 realization on a great scale in 1849, and more recently by Siemens in his combined 

 steam- and air-engine now in operation on the Continent, gave reason to expect that 



* In 1843, Mr. Joule announced that he had found that heat was evolved by the passage 

 of water through small tubes, and that each degree required for its evolution a mechanical 

 foice of 770 lbs. 



