Tables 228, 229. 



SPECIFIC HEAT. 



Specific Heat ol Water. 



The specific heat of water is a matter of considerable importance in many physical measure- 

 ments, and it has been the subject of a number of experimental investigations, which unfortu- 

 nately have led to very discordant results. Regnault's measurements, published in 1X47,* show 

 an increase of specific heat with rise of temperature. His results are approximately expressed 

 by the equation 



c^ 1 -\- .0004 / -(- 0000009 '^> 



which makes the specific heat nearly constant within the atmospheric range. A different equa- 

 tion was found from Regnault's results by Boscha, who thought the temperatures required cor- 

 rection to the air-thermometer. Regnault, however, pointed out thai the results had already 

 been corrected. Jamin and Amaury t found, for a range from 9"^ to 76° C, the equation 



c = I -\- .0011 i-\- .0000012^, 



which nearly all the evidence available shows to be very much too rapid a change. ^ViilIner 

 gives, for some experiments of Miinchhausen,t the equation 



c= I -\- .00030102/ 

 in vol. I, changed to 



<: = I + .COO425 1 



in vol. 10, for a range of temperature from 17° to 64°. In 1S79, experiments are recorded by 

 Stamo,§ by Henrichsen,|| and by Baumgarten, || all of them giving large variation with temper- 

 ature. 



In 1879, Rowland inferred from his experiments on the mechanical equivalent of heat that the 

 specific heat of water really passes through a minimum at about 30°. and he attempted to verify 

 this by direct experiment. The results obtained by direct experiments were not by any means 

 so satisfactory as those obtained from the friction experiment; but they also indicated that the 

 specific heat passed through a minimum, — but, in this case, at about 20° C. Further, direct 

 experiments were made in 1S83, in Rowland's laboratory, by Liebig, using the same calorimetric 

 apparatus ; and these experiments also show a minimum at about 20° C.lf Since the publica- 

 tion of Rowland's paper a number of new determinations have been made. Gerosa gave, in 

 18S1, a series of equations which show a maximum at 4°.4, then a minimum a little above 5^ and 

 afterwards a rise to 24°! Neesen** found a minimum near 30°, but got rather less variation than 

 Rowland. Rapp,tt taking the mean specific heat between 0° and 100° as unity, gives the equa- 

 tion 



c = 1.039925 — .007068 i -\- .00021255 ^ — .000001584 i^, 



which gives a minimum between 20° and 30° and a maximum about 70°. Volten JJ gives an 

 equation which is even more extraordinary with regard to coefficients than the last, namely, 



<- = I — .0014625512/ -\- .0000237981 /2 — .00000010716/''', 



which puts the minimum between 40° and 50°, and gives a maximum at 100°; which maximum 

 is, however, less than unity. Dieterici, in his paper on the mechanical equivalent of heat, dis- 

 cusses this subject ; but his own results being in close agreement with Rowland's, his table prac- 

 tically only extends Rowland's results through a greater range of temperature, assuming straight- 

 line variation to the two sides of the minimum. Rartoli and Stracciati *;§ found a minimum at 

 about 30°; while Johanson in the same year gives a minimum at about 4° and then a rise about 

 12 times as rapid as that of Regnault. Griffiths !l|| finds the equation 



r = I — .0002666 (/ — 15) 



to satisfy his experiments through the range from 15° to 26^. This agrees fairly well with Row- 

 land through the same range, and indicates that the minimum is at a temperature higher than 

 26°. 



The following table gives the results of Rowland, Bartoli and Stracciati, and Griffiths. The 

 column headed " Rowland " has been calculated from Rowland's values of the mechanical equiv- 

 alent of heat at different temperatures, on the assumption that the specific heat at 15° is equal to 

 unity. 



* " M^m. de I'Acad." vol. 21. t " Compt. Rend." vol. 70, 1870. 



t " Wied. Ann." vols, i and 10. § " Wied. Beib." vol.3. 



II "Wied. Ann." vol. 8. 



II Rowland, " Proc. Am. Acad." vol. 15, and Liebig, "Am. Jour, of Sci." vol. 26. 

 " "Wied. Ann." vol. 18, 1883. 



tt " Diss. Zurich." Jt " Wied. Ann." vol. 21, 1884. 



§§ "Wied. Heib." vol. 15, 1891. |||| "Phil. Trans." 1893. 



Smithsonian Tables. 



222 



