798 TRUEBLOOD. 



present writer's experiments, the pressure-coefficient of /x would still 

 be negative, in spite of the contrary evidence yielded by the work 

 which has been described. Enough weight is attached to this evidence, 

 however, to discount to some extent the deductions from the ammonia 

 equation, of which experimental verification at the pressure in question 

 is lacking, and, in view of the conflict of evidence as to sign, to regard 

 the pressure-corrections to the writer's observed ^I's as negligible 

 within the accuracy claimed for the /i of set-up S. 

 Goodenough ^^ has proposed the empirical equation 



(5) , = c + ^- (1 + Sapi) '^^ 



for superheated steam. He finds that this equation is in excellent 

 agreement with the specific volume determinations of Knoblauch, 

 Linde and Klebe.^* By means of well-known thermodynamic rela- 

 tions, the equations 



(.6) C,= <P(T) + ~rr^ V (1 + 2a V-) and 



'm {n +1) (1 + 3a;>' 



'!-.] 



^'^ " = c, L r» 



are deduced from it. By adopting for the arbitrary function 'P (T), 

 in (6), the form 



(8) ^(T) = a + ^T+^^ 



Goodenough further secures good agreement with the Cp determina- 

 tions of Knoblauch and Mollier ^^ and other experimenters. If we 

 calculate the value of {d(x/dp)T from (7), using the proper values of 

 the several constants,* and taking p = 4.0 kgm./cm.', T — 165° C. 

 ordinary = 438° C. abs., wefind {dfji/dp)T = + 0.014; °C. cm.ykgm.^, 

 which is of the same sign as the roughly approximate value derived 

 from the experiments with plug VI, though only about half as great. 



13 Properties of Steam and Ammonia, Wiley and Sons, 1915, p. 6. 



14 Mitt, iiber Forschungsarbeiten des Ver. d. Ing., 21, 33-55 (1905). 



15 Op. cit. 



* If p is in kgm./cm.^ v in m.Vkgm., T in °C. abs., Cp in kgm. cals./kgm. °C., 

 M in °C.cm.Vkgm.,then logm /3 = 3-67213, logm m = 8.59929, 3a = 0.19339, 

 n = 4, A = 0TffT2^^. a = 0-'^20, = 0.0002268, y = 7371. cis not strictly 

 constant, l)cing the specific volume of the liquid at the pressure under con- 

 sideration. If has the value 0.001083 m.Vkgm. in the present calculation. 



