Relation to Pr*8*wn and Temperature. 



505 



1 



^ClL 



/OJfi 



In case of paraffine, which is the first substance solid at 

 ordinary temperature, r 0p =l shows a somewhat larger variation 



of 6 relative to^>, the rate being 13° C. per atmosphere. The 



rate for thymol is '11° per 

 atmosphere, for toluidine 

 •10° per atmosphere, for 

 diphenyl amine *09 per at- 

 mosphere. In most of 

 these cases the expansion 

 difficulties, §14, make the 

 present results irregular, 

 particularly in the case 

 where two or more threads 

 are observed. At 310° the 

 behavior is usually excep- 

 tional, the discrepancy 

 which shows itself is simi- 

 lar to the case of ether and 

 alcohol, but much less pro- 

 nounced. 



In figure 4: I have rep- 

 resented these relations 

 graphically. It is seen at 

 once that the errors left 

 show no march. For di- 

 phenylamine the distribu- 

 tion is zigzag; for tolui- 

 dine and thymol in an 

 opposite sense for the two 

 cases. 



Taking these results 

 (0° to 185°) as a whole it 

 follows with remarkable 

 uniformity that if temper- 

 ature and pressure vary 

 linearly with each other, 

 at a rate of about -1° C. 

 per atmosphere, there will 



Fig. 4. Isometrics of Ether, Alcohol, Paraffine, be no change of volume. 

 Diphenylamine, Toluidine and Thymol. More rigorously : if ivith 



a, region of undercooling. the observed thermal ex- 



pansion compressibility be supposed to increase inversely as 

 the first power of the pressure binomial (§ 27), then temperature 

 and pressure must vary linearly to maintain constancy of 

 volume. Change of the state of aggregation is excluded. 

 The thermodynamic signification of this result has been sug- 

 gested in § 2. So far as the present results go, 0° to 185°, the 



c6o 



