614 BRIDGMAN. 



the value 32.0°. There are only three measurements of the transi- 

 tion IV-V. Lehmann (in a personal letter quoted by Behn) ^^ gives 

 — 16°, Wallerant gives the limits — 14° to — 16°, and Behn finds — 18°. 

 I have adopted this last value as more probably exact. For the melt- 

 ing point I have adopted the value of Lehmann, 168°, which is some- 

 what higher than the value given by Behn, 166°, as the average of 

 several other determinations. As already stated, I made no attempt 

 to measure this point myself. 



The change of volume at atmospheric pressure has been measured 

 by Bellati and Romanese ^* for the transitions JV-III and II-III. 

 For III-IV they give 0.01964 cm.^ per gm., but from a recomputation 

 of their data I should prefer the value 0.01955, although their data 

 show enough irregularity to admit a value as low as 0.01915. Behn ^^ 

 gives for this transition 0.022 (he pretends to give only two significant 

 figures), and I find by extrapolation from 77 kgm. (the extrapolation 

 correction is less than one percent) the value 0.02026. For the 

 transition II-III Bellati and Romanese give —0.00854 cm.^ per gm., 

 Behn gives 0.0081, and I find by extrapolation from 77 kgm. a some- 

 what lower value, 0.00758, the total extrapolation correction in this 

 case being about 3%. The change of volume I-II was not measured 

 by Bellati and Romanese. Behn gives 0.0132, and I find by an extra- 

 polation from 77 kgm. 0.01351. Lussana ^^ did not measure the 

 change of volume, but calculates from his other data for the pressure 

 effect the value 0.01465, assuming Bellati and Romanese's value for 

 the latent heat. The change of volume IV-V seems to have been 

 measured only by Behn, who found that it lies between the values 

 0.0155 and 0.0185, but was not able to get it more accurately because 

 of the lag already mentioned. 



The latent heats of transition have been measured only by Bellati 

 and Romanese/* who give for III-IV 5.02 gm. cal. per gm., for 

 III-II 5.33 cal., and for II-I 11.86 cal. I find by calculation from 

 Clapeyron's equation the values 4.66, 4.00, and 13.0 cal. respectively. 



The only measurements of the eft'ect of pressure are by Lussana ^^ 

 and Tammann.^® Tammann's measurements extended to 2800 kgm. 

 and include points on the II-III, III-IV, and II-IV curves, but he 

 made no measurements on the phase I. Lussana's pressure range 

 was only 250 kgm.; he measured the three transitions III-IV, III-II, 

 and II-I. Tammann states that there is no possibility of agreement 

 between his values, those of Lussana, and those computed from the 

 thermodynamic data of Bellati and Romanese. The discrepancy 

 stated by Tammann as existing between Lussana's data and those to 



