TABLES 228, 229. 



SPECIFIC HEAT. 



Specific Heat of 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. Kegnault's measurements, published in 1847,* show 

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

 by the equation 



c = i -f- -0004 / -j- 0000009 f2 < 



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 that the results had already 

 been corrected. Jamin and Amaury t found, for a range from 9 to' 76 C., the equation 



c = i -f- .001 1 / -)- .000001 2 1 3 , 



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

 gives, for some experiments of Munchhausen,}: the equation 



c= i -j- .00030102 / 

 in vol. i, changed to 



c= i -f .000425 1 



in vol. 10, for a range of temperature from 17 to 64. In 1879, 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 1883, in Rowland's laboratory, by Liebig, using the same calorimetric 

 apparatus ; and these experiments also show a minimum at about 20 C.1T Since the publica- 

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

 1881, 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 o and 100 as unity, gives the equa- 

 tion 



c= 1.039925 .007068 1-\- .0002 1 2 55/2 .000001584^, 



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, 



c = i .0014625512 / -|- .0000237981 f 2 .000000 1 07 1 6 i s , 



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. Bartoli 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 |||| finds the equation 



c = 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 1 5 is equal to 

 unity. 



Me"m. de 1'Acad." vol. 21. t " Cqnipt. Rend.'' vol. 70, 1870. 



' Wied. Ann." vols. i and 10. " Wied. Reib." voi. 3. 



' Wied. Ann." vol. 8. 



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

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



tt ' Diss. Zurich." n " Wied. Ann." vol. 21, 1884. 



'Wied. Beib." vol. 15, 1891. Illl "Phil. Trans." 1893. 



SMITHSONIAN TABLES. 



222 



