84 TABLE 40 (continued) 



PROBABLE VALUES OF THE GENERAL PHYSICAL CONSTANTS 



Thirteen methods, including the above, listed by Clarke, give a weighted mean 

 of 12.0025 ±0.00019. Aston 1 finds 0=12.0036, (limit of error 0.0012). 

 The mean of the final Clarke value and Aston's value is 12.003, and is adopted 

 here. 



C = 12.003 ±0.001. 



Calcium. — The atomic weight of calcium is needed for the grating space of 

 calcite. The value of Ca, accepted since 191 1, is 40.07. When readopted in 

 1925 by the International Committee, reference was made to the work of 

 Richards and Honigschmid. 2 These investigators precipitate CaCl 2 by a solu- 

 tion of Ag, and determine the amount of AgCl produced. They assume 

 Ag = 107.88 and 01 = 35.457. The final result is Ca = 40.075, based on four 

 determinations ranging from 40.085 to 40.070. It seems probable that the 

 Richards and Honigschmid value of 40.075 is the best. The probable error 

 0.005, i s verv uncertain. 



Ca = 40.075 ±0.005. 



The normal atmosphere (A„). — The normal atmosphere is defined as the 

 pressure due to a column of Hg 76 cm high, of normal density (o°C, A n ), 

 under normal gravity. 



The I.C.T. gives A n = 1.013250X io 6 dyne • cm" 2 , based on the definition of 

 A n as the pressure of a column of a liquid of density 13.5951 g per cm 3 , normal 

 gravity. The H.P. gives A n = 1.013253X io 6 , from the defining equation 

 A n = H n -/3„(Hg) • S,„(H 2 0) • g n , in which H„= height of normal barome- 

 ter =76.000 cm, p,, = normal specific gravity of Hg (at o°C, A n ), referred to 

 air-free water of max. density, 8 m (H 2 0) =max. density of water, g n = normal 

 gravity 4 = 980.665 cm • sec." 2 . Henning and Jaeger, 3 using the density of mer- 

 cury in the definition, investigate the most probable value of p n , then adopt 

 P» = I 3-5955- The value of S m (H 2 0) is 0.999973 g • cm -3 . The product 

 p„(Hg) •S m (H 2 0)= J D, i = 13.5955x0.999973= 13.595133 g-cnr 3 , agreeing 

 with the I.C.T. value to the six significant figures given by the I.C.T., but, 

 with the use of seven figures, leading to A„ = 1,013,253, as given by the H.P. 



Doctor Birge adopts as the most probable value of p„, the figure calculated by 

 Scheel and Blankenstein, 4 viz. 13.59546. D» = 13.59546x0.999973= 13.59509 

 g-cm -3 , and A n = 13.59509x76x980.665= 1.013249X io 6 dyne • cm -2 . This 

 should have a probable error of not more than two or three units in the last 

 digit, ±0.000003. 



The 45 atmosphere is obtained by the mere substitution of #45(980.616) 

 for g n . 



A n = (1.013249 ±0.000003) x 10 6 dyne • cm- 2 . 

 A 45 = (1.013199 ±0.000003) x 10 G dyne • cm 2 . 



a Proc. Roy. Soc, 115 A, 487, 1927. 2 Z. anorg. Chem., 163, 315, 1927. 3 H.P., 2, 490, 

 494. *Z. Phys., 31, 202, 1925. 



Smithsonian Tables 



