482 



PROCEEDINGS OF THE AMERICAN ACADEMY. 



here, 2200 against 2115. Tammann's pressure measurements were 

 made with a Bourdon gauge, which is not accurate at high pressures. 

 There are two pieces of evidence to show that Tammann's pressures 

 may be wrong ; the supposed inflection point on the I-L curve, which 

 has been already mentioned, and the behavior of Uie I-III curve above 

 the I-II-III triple point, which will be dealt with later. 





C3 



-.tJOO 



UJ 



2 



5 



|j_.190 



o 



C9 



Z 

 < 





-70° 



-00° -50° -tO° -30° 



TEMPERATURE 



•30° 



Figure 10. The change of volume III-I. 



The values for the change of volume obtained on April 18 with the 

 method described are given also in Table X., and shown in Figure 10. 

 The most striking feature is the enormous value of the change, being 

 about 20 per cent. The values extend into the unstable region over 

 a temperature interval twice the interval of stability, which is from 

 —22° to —35°. The values given have been corrected in the usual 

 way for the elastic distortion of the cylinder and the thermal dilatation 

 of the gasolene. Owing to the wide temperature range, this latter 

 correction is unusually large, rising to 6 per cent at the lowest tempera- 

 tures. The curve drawn through the points is forced a little so as to 

 give consistent results at the triple points, at —22° passing about 1/4 

 per cent too low and at —35° 1/4 per cent too high. 



The actual procedure in getting these change of volume points was 

 not exactly the ideal one described above. Below —35°, III is un- 

 stable, and the reaction to 11 might run at any time. The path 6 A 

 (Figure 8) was described successfully and two points found on the 

 lower end of BC before the reaction to II ran. On raising the tempera- 



